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' ‘:"'>a( ..,. ,. - 1‘ 1-1. .. ’ 37:1 .- 1—1-1: . - 1 . , . __‘_ '1:.'-,...,’ 4 , A ' "wn'O-vrq'~h: ”1 1 1”». . . m" 4; a ”.25. ' ~ 1-- N-u 111147.: Ah». ' I "on . Aux-.1; ; ' 1:2,? $1.333; 1'. Kw 11- ‘ . 91m}, Ticb ‘ ' . - ‘f: w» " "#1-: ;:‘114l077«'t>- .1 - win". r '1!- ’v- r-.,,. first ”4‘4 4.3:; ": 'rjt‘.‘ CHIGAN S ATE U V RSITY LIBRARIES Iiium\unu’uummm | um I: u 3 1293 00901 7421 This is to certify that the dissertation entitled HANDEDNESS AND SEX EFFECTS ON VISUOCONSTRUCTIVE AND VISJOPERCEPTUAL ABILITIES IN COLLEGE STUDENTS presented by Peter Jeffrey Snyder has been accepted towards fulfillment of the requirements for Ph.D. Psychoiogy degree in < 7 Major professor Lauren Julius Harris 28 February, 1991 Date MSU is an Affirmative Action/Equal Opportunity Institution 0-12771 W- —. ._ V ._ E _ __._. _ ._ ._ , .# LIBRARY Mlchlgan State University K PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE DATE DUE , l- l Eli—i Lil-Q |L__l| ll Jl ll ll MSU le An Affirmative AotiorVEquel Opportunity Institution omens-pt HANDEDNESS AND SEX EFFECTS ON VISUOCONSTRUCTIVE AND VISUOPERCEPTUAL ABILITIES IN COLLEGE STUDENTS BY Peter Jeffrey Snyder, M.A. A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Psychology 1991 ABSTRACT HANDEDNESS AND SEX EFFECTS ON VISUOCONSTRUCTIVE AND VISUOPERCEPTUAL ABILITIES IN COLLEGE STUDENTS BY Peter Jeffrey Snyder, M.A. To assess the relationship of handedness and sex to spatial ability, 109 left-handed and 115 right-handed American college students were given a 9-item version of Annett's (1967) hand-use inventory, a familial sinistrality questionnaire, and three different kinds of spatial tests: the Stafford Identical Blocks Test (SIBT; a 30-item multiple-choice "mental rotation" test), the Rey-Osterrieth Complex Figure Test (ROCF), and a drawing test (300) that required the subjects to add whatever lines were necessary to make a series of two-dimensional figures appear to be three-dimensional. The left-handers were further separated into subgroups based on consistency of left-hand preference across a series of unimanual tasks on the hand-use questionnaire. Based on the sample data, the results suggest that consistent (CLH) and inconsistent (ILH) individuals are about equally prevalent, for both males and females, in the general population of left-handers. A positive history of familial sinistrality (FS+) was found to be twice as common in left-handers as in right- handers, and there were no sex differences in the incidence of FS+. Secondly, although there were no differences in the incidence of FS+ between the CLH and ILH subgroups for females, the incidence of FS+ in the CLH subgroup was more than twice that found for the ILH subgroup among males. The results further show that left-handers can be subdivided into CLH versus ILH subgroups not only on the basis of motor skill, but also (at least in males) on the basis of certain neuropsychological differences. Specifically, although an overall sex difference was found on the SIBT, BDD, and ROCF (delayed condition only) tests, with the males outperforming the females on all three measures, for males the CLH subgroup performed significantly worse on the mental rotation test (SIBT) than the right- handed subgroup (with the ILH subjects performing only slightly worse than the right-handers). Therefore, where left-handers are found to report a greater incidence of FS+, or to be inferior to right-handers in mental rotation skill, it is CLH left-handers (males in particular) who are making the largest contribution to these effects. A full understanding of the phenotypic differences between these two subgroups of left-handers may provide the basis for increased understanding of the underlying mechanism(s) and inheritance of handedness. It is suggested that the discrepant findings in previous studies of the cognitive correlates of left-handedness are caused by the mixing of two neuropsychologically distinct subgroups of left-handers, at least for males. In memory of Alexander Romanovich Luria, whose writings inspired me iv ACKNOWLEDGEMENTS I am most grateful to my major professor and dissertation committee chariman, Dr. Lauren Julius Harris, for his guidance, wisdom, and for his patience in continuing to steer me on the path towards the completion of my doctoral studies. Lauren has been uniquely generous with his time and intellect, and my persisting interest in this field of study is due largely to the interest that he has shown in developing my skills as a psychologist. Dr. Harris is a careful scientist, a caring teacher, and a good friend. I am also indebted to the other members of my dissertation committee, Drs. Norman Abeles, C. Lee Winder, and Albert S. Aniskiewicz. Both Drs. Abeles and Aniskiewicz have provided careful supervision of my clinical neuropsychology training, at the MSU Psychological Clinic, Ingham Medical Center, and through the MSU Department of Psychiatry. Their supervision of my clinical work has served to lay the foundation for my future efforts to become a highly competent clinical practitioner. Dr. Winder, as my clinical psychotherapy supervisor for two years, never let me forget that it is important to treat the whole patient, as most any neurological insult will lead to possibly severe changes in personality, and in one's marital, family, sexual, occupational, and social functioning. My sincere gratitude is extended to my family. My father, whose lead I followed in seeking a career in psychology and the neurosciences, remains both my greatest supporter and my greatest critic. My mother, brother, and gramma Belle have provided a limitless supply of love and support - and have made it possible for me to prevail over some very difficult periods. Finally, without the daily encouragement, love, and good humour from my beautiful new bride, Bonnie, this manuscript may very well not have been written. Finally, I wish to acknowledge the assistance of both Rheiny Veii in helping to collect the data, and of the United States and Columbian Coffee Industries, who have made it possible for me to complete this project in such a timely fashion. vi TABLE OF CONTENTS ABSTRACT................................ ACKNOWLEDGEMENTS........................ LIST OF TABLES ......................... LIST OF FIGURES ........................ INTRODUCTION OOOOOOOOOOOOOOOOOOOOOCOOOOO LATERAL SPECIALIZATION OF COGNITIVE FUNCTIONS IN THE HUMAN BRAINOOOOOOOOOIOOOOOOOOOOOO "Mixed Speech Dominance" in Normal Left-Handers OOOOOOOOOOOOOOOOOOOOO "Mixed Speech Dominance" in Pathological Left-Handers ..................... Lateral Specialization of Speech and Language Functions ........... Lateral Specialization of Visuospatial Functions ........... HANDEDNESS 0.0.0....OOOOOOOOOOOOOOOOO0.. AGenetiC MOdel OOOOOOOOOOOOOOOOOOO Neuroanatomical Correlates of Handedness .. HANDEDNESS AND SPATIAL ABILITY ......... Handedness and Visuo-Perceptual Functions . Handedness and Visual Memory ...... Cognitive Deficits and Left-Handedness .... Possible Reasons for Discrepancies Fluid versus Crystallized Intelligence . Subgroups of Left-Handers ...... Handedness and Manual Praxis ...... SEX DIFFERENCES AND VISUOSPATIAL FUNCTIONS ..... Neuromorphology and Sex Differences vii ii ix xi 10 14 15 16 20 20 21 23 27 27 29 36 39 44 SEX BY HANDEDNESS EFFECTS ON VISUOSPATIAL FUNCTIONS ...................................... 45 Reasoning Ability .......................... 47 Familial History of Sinistrality (FS) ...... 50 Hemispheric Arousal Style .................. 54 THE CURRENT STUDY ............................... 57 Differences Between Current Study and PreVious ResearCh .....................O... 58 Summary of Predictions ..................... 61 METHOD .......................................... 64 Subjects ................................... 64 Materials .................................. 65 Procedure .................................. 80 Data Analyses .............................. 81 RESULTS ......................................... 83 Demographic Statistics . . . . . . . . . . . . . . . . . . . . . 83 Independent and Control Variables .......... 94 Dependent Variables ........................lOS Correlation Between Spatial Measures .......124 Multivariate Analysis (MANOVA) of the Dependent Measures . . . . . . . . . . . . . . . . . . . . . . . .125 Discriminant Function Analyses .............126 DISCUSSION ........ ..... .0.......................l34 GENERAL DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . 0 I O O . . .148 CLINICAL IMPLICATIONS AND FUTURE DIRECTIONS .....154 NOTES ...........................................157 APPENDIX A.................. ..... .0..............16O REFERENCES ......................................186 viii 10. ll. 12. 13. 14. 15. LIST OF TABLES Dependent Measures................................. 69 Criteria for Five Levels of ROCF Organization...... 76 Selection of the Three Independent Raters for Every 25th ROCF DraWing....................... 77 Subject Groups: Sex X Handedness................... 83 Subjects' Ages (in years): Sex and Handedness Groups ..........................................0 83 Subject Subgroups: Sex X Handedness................ 85 Percentage of CLH, ILH, and RH Subjects Favoring the Right Hand (or with no Hand Preference) for Specific Unimanual Tasks.......... 86 Sex Differences on Laterality Index (L.I.) scores ..........................................O 89 Average Scores (Dominant and Non-Dominant Hands) on the Performance Test of Hand Dominance for EaCh subgroup ...................0................ 90 "Hand Difference" Scores on the Performance Test of Hand Dominance for Each Subject SUbgroup ....................................O.... 9]. Scores on the Chimeric Faces Test .................101 Scores on the Stafford Identical Blocks Test ..... 105 Sample Sizes of Each Subject Group for the 336 Scored ROCF Drawings......................... 109 Sex By Handedness Differences on the ROCF (Delayed Recall Condition): Results of MANOVA Procedures ....................................0. 112 Descriptive Statistics for Each Subject Group for the "Delayed Recall" Measures of the ROCF ..................................00.... 113 ix 16. 17. 18. 19. 20. 21. 22. 23. Sex By Handedness Subgroup Differences on the "Intersections" Measure of Performance on the Delayed Recall Condition of the ROCF...... 115 Sex By Handedness Subgroup Differences on the "Alignments" Measure of Performance on the Delayed Recall condition Of the ROCF.OOOOIOOOOOOOOOOOO... 116 Handedness By FS Differences on the Index Scores for the 3DD.OOOOOOOOOOOOOCI...OOOOOIOOOOOOOOO0.0. 123 Pearson-r Correlation Coefficients for the SIBT and 3DD O0.0...O....00...OOOOOIOOOOOIOOOOOOO 124 Discriminant Function Analysis Between Male and Female Subject Subgroups with the SIBT, 3DD, and Vocabulary Tests as the Discriminating Variables ....................................... 128 Discriminant Function Analysis Between Female Handedness Subgroups with the SIBT and 3DD as the Discriminating Variables.................. 129 Discriminant Function Analysis Between Male Handedness Subgroups with the SIBT and 3DD as the Discriminating Variables.................. 130 Discriminant Function Analysis Between Male Handedness By FS Subgroups with the SIBT and 3DD as the Discriminating Variables.............. 132 7A. 73. 8A. 8B. 9A. 9B. 9C. LIST OF FIGURES Waber - Holmes Scoring System for the Rey - Osterrieth Complex Figure Test.............. Frequency Distributions for Both Dextrals and Sinistrals on the Laterality Index (L.I.), Where 9 = Exclusive Left-Hand Use, and 45 = Exclusive Right-Hand Use .................... Distribution of ‘Hand Difference Scores' on the Motor Speed Test, Where a High Score Indicates a Large Difference in Motor Speed Between Subjects' Dominant Hand and Non-Dominant Hand ................................ Percentage of FS+ and FS- Subjects in Each subgroup OOOOOOOOOOOOOCOCOOOOOOOIOOOOOOOOOIOOOO0.0 Sex Differences for Performance on the 32-Item Vocabulary Test (maximum range = 0 - 60) ......... Performance of Dextrals and Sinistrals on the Chimeric Faces Test, Where -1.0 = Exclusive LVH Response Style; and +1.0 = Exclusive RVH Response StYle 0.0.0.0....0..0.00....OOCOOOOOOCOOOOOOCCOOCO Performance of Dextral Subjects on the Chimeric Faces TeSt OOOOOOOOOOOOOOOOOOOOOOOO00.000.00.00... Performance of CLH/ILH By Sex Subgroups on the Chimeric Faces TeSt O0......OOOOOOOOOOOOOOOOOOOOOO Males Performance on Stafford Identical BIOCkS TeSt .0...O...OOOOOOCOOOOOOOOOOOOOO0...... Females Performance on Stafford Identical BIOCkS Test OOOOOOOOOOOOOOOOOOOIOOOOOOOIOOOO.I... Sample 3DD Drawing: "Completely Failed Attempt“ . Sample 3DD Drawing: ”Poor Attempt" .............. Sample 3DD Drawing: "Reasonable/Good conStruCtion" OCOCCOOOOOOOOOOOOOOOO0.00.00.00.00. xi 75 88 93 96 99 103 104 104 107 107 118 118 119 9D. Sample 3DD Drawing: "Excellent Construction" .... 119 10. Distributions of 3DD Index Scores for Both Males and Females, Where a High Score Indicates Better Performance on the 3DD.... 121 xii INTRODUCTION Man's ability to perceive, integrate, and organize his environment has long been a focus of scientific study. It is our higher cognitive functioning, our capacity to abstract salient features from our environment and to symbolize, conceptualize, and express our experiences, that many feel distinguish us as a species. This thesis focuses on one aspect of higher cognitive functioning - the perception and manipulation of visual-spatial information, such as the ability to mentally "rotate" a two-dimensional figure as if it were three-dimensional. Much research over the past century has pointed to the predominant role played by the right cerebral hemisphere in mediating Visuospatial functioning (cf. Luria, 1966). Over this same period, much research also reveals a great range of individual differences in Visuospatial abilities within the population. The possibility arises that individual differences in the cortical organization for spatial functions might account, in part, for individual differences in spatial ability. The possibility also occurs that these individual differences are related to certain subject variables. Previous research suggests that two such variables are sex and handedness, both of which have been 2 shown to be correlated with different patterns of lateral specialization for cognitive functions. The purpose of the current study is to better understand how these variables work, separately and in combination, to influence spatial ability, and whether they are associated with variations in lateral cerebral specialization of Visuospatial functions. LATERAL SPECIALIZATION OF COGNITIVE FUNCTIONS IN THE HUMAN BRAIN Questions about the evolutionary bases and adaptive value of lateral specialization of the human brain have attracted interest since Broca's day in the 1860's. A paradigm that has proven to be especially useful in the study of lateral specialization is the study of patients whose neocortical commissures have been surgically transected for the control of medically refractory epilepsy. These studies have confirmed the principle that the left hemisphere plays the leading role in language functions, speech in particular. The fact of lateralization for speech and language functions has provoked speculation about its evolutionary history. Levy-Agresti and Sperry (1968) have hypothesized that during hominid evolution the "gestalt" perception of external stimuli became lateralized to the hemisphere that is typically non-dominant for speech as a consequence of Esome inherent antagonism between verbal and Visuospatial 3 functioning. Levy (1969) has suggested that this development may also have come at a certain cost, so that people with "partial language competency in both hemispheres" may perform relatively poorly on tests of Visuospatial ability. Levy also designated left-handers as examples of persons fitting this description. "Mixed Speech Dominance" in Normal Left-Handers The inclusion of left-handers in the category of individuals with partial language competency in both hemispheres, or "mixed speech dominance" (MSD), is supported by evidence from three sources: 1) studies using the Intracarotid Amobarbital Procedure (IAP) on patients with late-onset focal lesions (an invasive procedure whereby the language zones of one hemisphere are selectively anesthetized by the intracarotid administration of a barbiturate); 2) clinical studies of left- and right-handed adults who have suffered left hemisphere injuries; and~3) non-invasive studies of normal persons using such methods as dichotic listening. In her studies with the IAP, Milner (1975) found no evidence of MSD in a group of 140 right-handed patients with late-onset epilepsy. Instead, 95-98% of these patients showed lateralization for speech to the left hemisphere (see also Rasmussen & Milner, 1977). By contrast, Sinistrals with late-onset epilepsy (implying that their left- handedness is not due to an early left hemisphere injury) 4 show a heterogenous pattern of lateralization of speech functions. In Milner's (1975) study, 15% of a sample of 122 left- or mixed-handed epilepsy patients were determined to have MSD. In other studies, estimates of MSD ranging from 0% to 50% of developmentally normal left-handers with right hemisphere lateralization for speech have been reported (e.g., H caen & Sauget, 1971: Rasmussen & Milner, 1977; Satz, 1979: Strauss, Wada, & Satz, 1988 [cited in Satz, Strauss, Wada, & Orsini, 1988]: see review by Snyder, Novelly, & Harris, 1990). Despite the apparent lack of agreement as to the incidence of MSD within the general population, most investigators agree that where MSD is found, the individuals invariably are sinistrals (Chesher, 1936: Goodglass & Quadfasel, 1954; Humphrey & Zangwill, 1952: Kimura, 1983a; but see Loring et al., 1990). Converging evidence comes from clinical studies that reveal a higher incidence of speech disorders after right-sided lesions in sinistrals as compared to dextrals. In addition, dichotic listening studies with normal subjects show a weaker pattern of lateralization for the interpretation of verbal stimuli in sinistrals as compared to dextrals (Kimura, 1983b1). Given the evidence that MSD (and right hemisphere dominance for speech) in developmentally normal individuals is largely restricted to adextrals, Levy (1969) chose left- handers to test her hypothesis relating MSD to spatial ability. She compared 10 sinistrals and 15 dextrals on the 5 verbal (VIQ) and "performance" (PIQ) cluster scores on the Wechsler Adult Intelligence Scale (WAIS). Although the two groups did not differ on VIQ (p<.10), they did differ on PIQ with the sinistrals scoring well within the normal range but significantly worse than the right-handers (p<.002). Levy therefore concluded that the left-handers' presumably weaker lateralization for speech and language had interfered with their ability to perform the non-verbal tasks comprising the performance subtests of the WAIS-R. "Mixed Speech Dominance" in Pathological Left-Handers Thus far we have considered the proposition that, at a group level, MSD in neurologically normal persons is more common in left-handers than in right-handers and that this has consequences for certain cognitive abilities. In individuals who are pathologically left-handed (due to an early insult to the periopercular zones of the left cerebral hemisphere), there is an even higher propensity for MSD than in comparable groups of normal left-handers because the neuropathology that shifts control of handedness to the right hemisphere also tends to shift control of speech and other language functions, a phenomenon first alluded to by Broca (1865) and subsequently confirmed in many clinical studies (e.g., Gardner, 1941: Zaidel, 1983; Satz, Orsini, Saslow, & Henry, 1985; Bishop, 1988; see review by Harris & Carlson, 1988). 6 Will MSD that has been induced by left hemisphere neuropathology also have consequences for non-verbal functions? Some evidence suggests that it will. Lansdell (1962) tested patients who had suffered early damage to the periopercular zones of the left hemisphere with subsequent shifting of speech dominance into the right hemisphere (determined by IAP). The result was that patients with early left-hemisphere damage and subsequent right-hemisphere speech dominance scored higher on the verbal subtests of the Wechsler-Bellevue Intelligence Scale than on the nonverbal subtests, whereas patients with early left-hemisphere injuries who remained left-hemisphere dominant for speech did worse on the verbal than on the nonverbal subtests. In both groups of patients, many also were left-handed, but here both the left-handedness and the MSD stemmed from early neurological insult. In the first of Lansdell's two subject groups, listed above, the hypothesized explanation for the apparent decrease in Visuospatial ability as a result of a shift in speech and language dominance to the right hemisphere has been termed the "crowding hypothesis." The hypothesized crowding of verbal and non-verbal functions in the right-hemisphere has been invoked to describe both the possible cortical re-organization of cognitive functions following early left-hemisphere injury, as well as a result of amodal organization of the brain for a subset of neurologically normal, genetic left-handers. Lansdell (1969) subsequently found that if left hemisphere brain 7 damage occurs before 5 years of age, there is a greater likelihood that verbal development will progress at the expense of well-developed nonverbal abilities. It is unclear how to understand the term "crowding" at the physiological level. One possibility is that verbal functions that are subsumed by the right hemisphere are "given" priority for limited space, thereby reducing the amount of cortical tissue necessary for the unimpeded development and control of Visuospatial abilities. Specifically, functionally disparate neural networks might "compete" for synaptic sites during the embryological development of the cortex, thus hindering the development of neural networks subserving spatial functions if the neural architecture leading to the cortical mediation of language and speech is favored ontogenetically. Another possibility is that in individuals with early left-sided trauma, the re-organization of speech into the right hemisphere causes cortical activity mediating verbal functions, now located in close proximity to cortical areas responsible for Visuospatial functions, to interfere with the neuropsychological mediation of Visuospatial functions. This latter interpretation is consistent with Levy's (1969) evolutionary model for the development of lateral specialization, that is, to separate potentially incompatible cognitive processing modalities into different hemispheres. 8 Although the "crowding" hypothesis has stimulated much new research, both with non-clinical and clinical populations, the term "crowding" is questionable as a valid characterization of the neural processes involved in hemispheric specialization (Nottebohm, 1979). The reason is that this metaphor contradicts modern neurobiological notions of brain organization, which posit circuit modules that can be variously combined and recombined to provide greater functional capacity and diversity (cf. Edelman, Gall, & Cowan, 1984). It also is doubtful that the linguistic categories used to describe psychological functions represent size-specific parcels of neuroanatomical space (Michel, 1989). Until more is known about the relation between different structural neuroanatomical patterns, the ontogeny of neurophysiological processes, and specific aspects of psychological functioning, there appears to be little substantive value in characterizing hemispheric specialization as territorial competition for brain space. Indeed, it is possible that the co-localization of cortical regions responsible for subserving language and spatial functions, in the same hemisphere, could serve to either hinder or support Visuospatial functioning. For example, localization of speech and/or language zones near cortical areas responsible for spatial functions might serve to benefit Visuospatial functioning if the spatial task can be accomplished, in whole or in part, by verbal strategies. 9 For the time being, it may be best to use the term "crowding" heuristically. Lateral Specialization of Speech and Language Functions There has been much progress in the study of human lateral specialization since the early reports cited above. In particular, we have a better understanding of the nature and extent of lateral specialization of both verbal and Visuospatial functions. Research over the past two decades has not supported the simple model that language functions are strictly lateralized to the left hemisphere. Although there is overwhelming evidence that speech is lateralized to the left cerebral hemisphere in nearly all dextrals (Rasmussen & Milner, 1977) and in most sinistrals (e.g., Kimura, 1983a), there is mounting evidence that the right hemisphere also plays a role in receptive language functions in neurologically normal individuals. Zaidel (1985) and others (see review by Chiarello, 1988) have argued that the right hemisphere in normal persons has limited but measurable competence for comprehending both spoken and written language but that it is generally impoverished in its ability to produce meaningful verbal expression (in dextrals), which competition from the speech-dominant left hemisphere makes difficult to observe in any case (Levy- Agresti & Sperry, 1968: Butler & Norrsell, 1968). Consistent with this view is evidence that globally aphasic 10 patients show some recovery of language comprehension, even when a lesion amounting to a left-sided hemidecortication is present (Kertesz, 1979, p.142). New research also has demonstrated an important right— hemisphere role in the interpretation and modulation of affect and prosody in speech, and in the comprehension of humor. Although patients with right-hemisphere damage are still able to appreciate the variety of forms of humorous stimuli, they show "particular difficulty in resolving the incongruity of humor and integrating the elements into a 0.123). - coherent whole" (Bihrle, Brownell, & Gardner, 1988, The authors suggest that the reason is that these patients possess "rigidity of interpretation, literalness, and inattention to relevant detail" in their approach to the comprehension and interpretation of verbal humor. Lateral Specialization of Visuospatial Functions The new evidence of right-hemisphere linguistic functions raises questions about the role language might play in the completion of seemingly non-verbal, Visuospatial cognitive tasks by the right hemisphere. At the same time, new work has demonstrated the shared role of the cerebral hemispheres in the perception, interpretation, and manipulation of Visuospatial stimuli (e.g., Geschwind and Kaplan, 1962). This raises questions about the possible role of spatial abilities for the successful completion of language tasks, meaning that just as language factors may 11 affect spatial processing, so might spatial factors affect linguistic processing, such as language comprehension (e.g., Luria, 1966, pp. 154-158, 384-389). One example of "bilateral" contributions to spatial functioning can be observed by performance on the block design subtest of the WAIS-R, where the subject, using red and white blocks, must duplicate a series of modal designs (both 2x2 and 3x3 design matrices). Kaplan (1988) has found that when commissurotomy patients perform this task with only the left hand (or right hemisphere in isolation), they preserve the design contour but lose the internal detail. The performance is much like that of patients with left- hemisphere lesions (Kaplan, 1988). When the same commissurotomized patients used the right hand (or the left hemisphere in isolation), the results were fundamentally the reverse of the designs produced by the right hemisphere. Now, the matrices were rarely preserved, and the patients instead tended to pile the blocks on the right side (in the right hemiattentional field), and some of the model design's internal details were relatively preserved in their right-hand productions. These clinical data suggest that in the construction (and possibly perception) of a visual design (e.g., a drawing test), the left hemisphere contributes to the production of internal details, while the right hemisphere complements this effort by reproducing the design's outer shape. 12 A similar pattern of errors has been observed in patients with focal parietal lesions. Patients with right- sided lesions failed to preserve the outer shape of the design but conserved some of the internal details, whereas patients with left-sided lesions maintained the outer configuration without regard for the internal details (Kaplan, Palmer, Weinstein, & Baker, 1981). Kaplan (1988) has reported identical findings in both commissurotomy and focal-lesioned patients on the Object Assembly subtest of the WAIS-R and on the Rey-Osterrieth Complex Figure Task (ROCF). Evidence that the two cerebral hemispheres contribute in different but complementary ways to the completion of a visuoconstructive task (e.g., Block Design, Object Assembly, ROCF) also has been found in studies of neurologically normal subjects. Kee, Bathurst, and Hellige (1984) employed a dual-task paradigm using concurrent finger-tapping and block design tasks with right-handed college students. The result was more left- than right-hand disruption of finger tapping when subjects were required to complete a block design manually, using their non-tapping hand, whereas the reverse pattern was found when the subjects had to complete the same test "mentally.“ These results suggest that there is more right than left hemisphere processing activity during actual performance of a visuoconstructive task, but more left hemisphere activity when the same test stimuli are manipulated mentally. 13 Kee et al.'s results are consistent with those of an earlier study by Ornstein, Johnstone, Herron, and Swencionis (1980). Using EEG alpha suppression as an index of hemispheric activation, these investigators concluded that a task requiring mental rotation of spatial stimuli is more likely to involve verbal strategies in part (greater left- hemisphere involvement), whereas right-hemisphere activation is greater when a visuoconstructive approach is required. These studies lead to several general conclusions. First, the two cerebral hemispheres contribute in different but complementary ways to the interpretation and construction of a visual array. Secondly, normal individuals show a relatively greater margin of right- over left-hemisphere activation during the completion of a Visuospatial task, depending on whether the task is primarily visuoconstructive or visuoperceptual. These findings indicate that as with language comprehension, the perception and manipulation of Visuospatial stimuli consist of a multidimensional set of inter-related functions. The neuropsychological investigation of Visuospatial functions therefore must consider the specific task demands of the non-verbal task(s). It must ask what specific patterns of performance on that task might mean with regard to cerebral distribution of non-verbal functions, as opposed to similar performance on a separate task that requires different cognitive strategies for its solution. 14 This progress in our understanding of the neurocognitive requirements for the successful completion of specific Visuospatial tasks suggests further questions. First, do certain subgroups of individuals, but not others, show reliable overall differences in their performance on these tasks? Second, what can such differences tell us about group (and individual) differences in the neuropsychological organization of Visuospatial functions? Two dimensions of individual differences, handedness and sex, for which differing patterns of performance have been observed on a variety of Visuospatial tasks, will be examined below. HANDEDNESS In the years since Levy's (1969) report of handedness differences in PIQ, a better appreciation of the complexities involved in the analysis of handedness has developed. We now have a deeper understanding of the biological substrates and neurological correlates of handedness as well as a better understanding of the) phenotypic expression of handedness itself. Both of these developments were important in the framing of the current investigation. 15 A Genetic Model Of all primate species, only Homo sapiens sapiens show a population bias toward preferential use of one hand (Corballis, 1989). The population bias is of long-standing. Analysis of cave drawings suggests that it extends back at least 5,000 years (Coren and Porac, 1977), and the microscopic analysis of patterns of wear on tool specimens (shards of stone) points to a considerably longer period than that (Corballis, 1989). What this analysis shows is that tools used during the Upper Paleolithic period (35,000 - 8,000 B.C.) more often have wear patterns on the right side, indicating that if these tools were used to scrape in a downward motion, the users held the shards more often in the right hand (Semenov, 1964 [cited in Corballis, 1989]). If the population bias of H. sapiens sapiens toward right-handedness extends back for 10,000 to 35,000 years, it seems likely that this species characteristic is genetically determined. There have been several efforts to specify the actual genetic mechanism. Perhaps the most widely accepted theory was proposed by Annett (1981). Annett proposed that both handedness and cerebral asymmetry for certain cognitive functions are influenced by a single "right shift" gene with two alleles. The dominant allele (RS+) establishes left- cerebral control for speech and right-handedness in those who carry it. In those who are homozygous for the recessive allele (RS-), there is no bias towards either right- or 16 left—handedness, and such individuals, considered collectively, may show handedness and lateralized cerebral dominance for speech but no strong bias towards either side. If the proportions of the two alleles are equal in the population (balanced polymorphism), the number of heterozygotes will equal about 50% of the population. If so, the proportion of the population homozygous for R8- will equal approximately 25%, and in the absence of cultural pressures against left-handedness, about half will become left-handed. This prediction, in fact, fits well with the finding that in societies without an explicit bias against left-handedness, such as would be expressed in rules or traditions actively discouraging left-hand use for writing and other public acts, the prevalence of Sinistrality generally rests at about 12.5% of the population (Corballis, 1983), although even in these cultures, many covert biases remain (see review by Harris, 1990, pp. 195-196). Neuroanatomical Correlates of Handedness Broadly speaking, voluntary control of the upper limbs and hands relies on the synchronous operation of both cortical and subcortical mechanisms, effected through monosynaptic and multisynaptic tracts that originate in cortical grey matter and descend to synapse on spinal neurons. A review of the three descending motor systems (corticospinal, ventromedial, and lateral brain stem systems) mediating praxis of the hands and distal portions 17 of the upper limbs, may be found in Harris and Carlson (1988). In contrast to our advanced level of understanding of the anatomical and physiological factors underlying hand control, we still know very little about the underlying neurological basis for hand preference. One focus of attention has been on the cerebral hemispheres. Over the last twenty years there has been a spirited search for anatomical asymmetries between the hemispheres, and a no-less spirited debate on what any such asymmetries might mean. The rationale for this search lies in the assumption that asymmetries are clues to understanding lateral functional specialization. Witelson (1980) attributes this assumption to Geschwind and Levitsky's (1968) confirmation of earlier work from the 1920's showing that the opercular region of the Sylvian fissure (known to be crucial for language comprehension) is typically larger on the left side than the homologous areas on the right side. Several studies (Teszner, Tzavaras, Gruner, & Hecaen, 1972 [cited in Witelson, 1980]: Wada, Clarke, & Hamm, 1975: Witelson and Pallie, 1973, Pieniadz & Naeser, 1984) have provided corroboratory evidence that the planum temporale, the area of cortex on the superior surface of the temporal lobe posterior to the primary auditory cortex (Heschl's gyrus), is larger in the left hemisphere than in the right in approximately 70% of all brains studied (for review, see Witelson, 1977, 1980, 1988). Similarly, Albanese, Merlo, Albanese, and Gomez (1989) found 18 asymmetries, favoring the left side, in the weight and surface area of the posterior portion of the inferior frontal gyrus ("Broca's area" -- pars opercularis and triangularis caudalis), an area important for motor coordination of speech. Other research, however, indicates that the asymmetry in surface area appears only when the entire anterior speech region, including both the visible cortex and that buried in the sulci, is considered (Falzi, Perrone, & Vignolo, 1982). Still other neuroanatomical asymmetries that have been reported include larger motor pyramidal tracts on the right side, a longer occipital horn in the left lateral ventricle, and a variety of asymmetries in cortical vascularization. According to Witelson (1980), however, the association of these morphological asymmetries with functional asymmetry "is less obvious and more equivocal" than is the case for the temporal lobe asymmetry (p. 80). The asymmetries listed above are found in right-handers or in unselected samples of populations where handedness was unknown but in which we can presume that right-handedness was the norm. One reason to suppose that these asymmetries have something to do with handedness, however,'is that the asymmetries are less clear or consistent in adextrals. For adextrals, or left-handers, the pattern of neuroanatomical asymmetry instead is far more heterogeneous. This may imply that adextrals do not fit neatly into one homogenous group 19 but consist instead of separate subgroups with measurable between-group differences in neuromorphology. Why might the finding of greater heterogeneity of (cortical) anatomical asymmetries in left-handers be important? One possibility is that certain cognitive functions (e.g., speech) are more bilaterally organized in left-handers, and because we can conceive of a multitude of possible organizational patterns to foster greater interhemispheric cooperation, a more heterogeneous pattern of cortical asymmetries would be expected. One prediction derived from this hypothesis is that the commissural pathways, necessary for interhemispheric communication, are more extensive (e.g., larger) in sinistrals than in dextrals. Support for this prediction is mixed. Witelson (1985, 1989) made outline drawings of the corpus callosum, from photographs of the medial view of midsaggital hemisections, and found the posterior body segments of the corpus callosum (especially the isthmus) to be 11% larger in adextrals than in right-handers. However, Kertesz, Polk, Howell, and Black (1987), using larger sample sizes (52 right- and 52 left-handers) and MRI imaging of the corpus callosum in intact brains, found no significant handedness differences for either total collosal area or for the splenium-to-genu size distribution. 20 HANDEDNESS AND SPATIAL ABILITY Since Levy's (1969) original report linking left— handedness to poorer spatial ability, there have been many further studies of the relationship of handedness to spatial ability. The results provide mixed support for Levy's hypothesis. Handedness and Visuo-Perceptual Functions One category of tests has been tests of visuoperceptual functions in which subjects are asked to infer what the total configuration of a geometric design from incomplete information about the stimulus. One of the first of these studies was by Nebes (1971b). Previously, Nebes had found that right—handed commissurotomized subjects were more able to "infer the total stimulus configuration from incomplete information" when the information was confined to the right hemisphere (Nebes, 1971a). Nebes (1971b) then assessed neurologically normal right- and left-handers for the same ability. He compared the performance of 26 self-described left-handers with 26 self-described right-handers on the Arc-Circle Test, which required the subject to feel an arc (part of a circle) that is hidden from view and then to point to the correct circle out of an array of circles varying in size. The left-handed group did significantly worse than the right-handers with either hand (p<.002). Other investigators, however, have not replicated Nebes' 21 findings with this test (Hardyck, 1977: Kutas, McCarthy, & Donchin, 1975). In other early studies, right-handers also have been reported to be more proficient than left-handers on copying and maze tasks (Flick, 1966) and on tasks requiring the subject to identify the sidedness of pictured body parts, to determine the localization of tactile stimulations, and to make mirror-tracings (Silverman, Adavai, & McGough, 1966). In contrast to these reports of inferior performance by left-handers on visuoperceptual tasks, there are several reports suggesting just the reverse, namely, that left— handedness is more common in occupations -- art (Mebert and Michel, 1980) and architecture (Peterson and Lansky, 1974) - - that presumably select for excellent Visuospatial ability. Peterson and Lansky (1974), for example, found that of 484 male architecture students surveyed, 16.3% reported being left-handed.2 When assigned to construct a 2-dimensional maze according to a difficult set of design requirements, all of the left-handers designed their mazes correctly, whereas the dextrals made many errors (p<.001). Both the right- and non-right-handers, however, were equally able to solve mazes of comparable difficulty to the ones they were asked to design themselves. Handedness and Visual Memory A second major category of tests in which left- and right-handers have been compared is tests of Visuospatial 22 memory. For example, Nebes and Briggs (1974) tested 120 right-handers, left-handers, and subjects whom they called mixed-handed (the subjects were separated into the three groups on the basis of their responses to a modified version of Annett's (1967) handedness questionnaire) on tests of visual memory and verbal memory. On the verbal memory test, no group differences were found. On the visual memory test, however, the right-handers made more correct responses (p<.025) and fewer errors (p<.05) than the left- and mixed- handers, who did not differ from each other. In a second study, Nebes (1976) examined the use of visual memory in right- and left-handed undergraduates separated on the basis of responses to his adaptation of Annett's (1967) questionnaire. He found no differences between the two groups in their performance on a verbal recall test (that is, a test that discouraged the use of visual imagery) and the Recognition of Random Shapes Test (a test that encouraged the use of visual imagery). In light of his previous findings (Nebes & Briggs, 1974), Nebes (1976) suggested that group differences now were absent because, unlike the previous study, the subjects were required only to recognize shapes upon immediate recall (rather than having to reproduce them). Nebes concluded that the left-handers show a decrement, relative to dextrals, in the manipulation of Visuospatial stimuli following the verbal encoding of such stimuli for later recall. Similar results have been reported by several other 23 investigators (e.g., Levy, 1969; Miller, 1971; Harshman, Hampson, & Berenbaum, 1983: McGlone & Davidson, 1973). Finally, in still another study of handedness and visual memory, Weinstein (1987) used the ROCF. First published in 1941 by the Swiss neuropsychologist, Andre Rey, the ROCF is useful for evaluating an individual's ability to plan, organize, and assemble complex visual information (Goodglass & Kaplan, 1987). The ROCF also tests an individual's ability to retrieve a complex visual stimulus from short-term memory (STM) and after a 20-minute delay period. In Weinstein's study of female college students, left-handers with a math/science major (presumably being those students who have chosen fields of study requiring well~developed spatial abilities) produced the best copies and drawings from memory, whereas the poorest drawings were made by right-handed non-math/science majors. These results therefore do not agree with previous findings. They also suggest that intellectual interests (as determined by the subjects' choice of academic major) might be useful in predicting ROCF performance. Cognitive Deficits and Left-Handedness In several of the previous investigations reporting poorer performance by left-handers than by right-handers, the authors have described their left-handed subjects as showing performance and/or perceptual "deficits" or "deficiencies" in comparison with right-handers. The term 24 "deficit" implies a clinically significant impairment of function or ability. It is important, then, to examine more closely the issue of possible cognitive deficits, perhaps restricted to more abstract reasoning functions, associated with Sinistrality. Historically, left-handedness has been associated with a wide range of cognitive deficits, and folk wisdom has often linked left-handedness to a variety of undesirable personality traits (Harris, 1990). For example, Lombroso (1903) reported that adextrality was more common in criminals than in law-abiding citizens. Compared to the normal population, left-handedness has also been reported to be more prevalent among the mentally retarded (Gorden, 1920) and epileptics (Mayet, 1902, cited in Gordon, 1920; see reviews by Harris, 1980; Harris & Carlson, 1988). Recently, a great deal of research has focused on the relationship between handedness and posited cognitive deficits. As mentioned previously, Lansdell (1962, 1969), in his study of left temporal lobe epileptics, found that if seizure onset occurred prior to age five, the patients showed relatively fewer deficits on verbal scores of the Wechsler-Bellevue, and greater deficits on the non-verbal scores. All of his subjects were right hemisphere speech— dominant (determined by IAP), leading Lansdell to conclude that the sparing of language function was caused by the development of language representation in the right, non- 25 epileptogenic hemisphere at the expense of Visuospatial functions typically subsumed by the right hemisphere. As noted earlier, there also is evidence that when language shifts to the right hemisphere in response to a pathological process of early onset, a related possible consequence for genotypic right-handers is pathological left-handedness (PLH) (Teuber, 1974; see Harris & Carlson, 1988, for a review). For example, Satz, Orsini, Saslow, and Henry (1985) found that 10 of 12 patients with early left hemisphere damage had Verbal I.Q. (WAIS-R) scores at least 15 points higher than their Performance 1.0. (non-verbal subtests) scores. This led Satz et al. (1985) to suggest that a deficit in Visuospatial ability is a marker for PLH. The prediction of a specific, atypical pattern of cortical specialization in response to neural insult stands in contrast to Levy's original prediction of a specific pattern of lateral specialization in neurologically normal, genotypic left-handers. Some investigators, however, have gone so far as to propose that, in contrast to the two-type model of left-handedness (acknowledging that left-handedness may result from either normal genetic variation or early pathology, all left-handedness may arise from a pathological process (Bakan, Dibb, & Reed, 1973). By implication, these investigators believe that any sign of poor performance, across a variety of cognitive domains, by ostensibly neurologically normal left-handers arises from the same neurodevelopmental anomaly that causes sinistral hand 26 preference (the evidence for this hypothesis is weak, and most researchers reject it in favor of the 2-type model; see Harris & Carlson, 1988). Despite their differences, both the one-type and two-type models of left-handedness "assume that cognitive ability is related to the extent of the cortical neural networks serving a given function. Below- average spatial ability in the left-hander, then, is seen as resulting from an under-representation of these neural regions" (Lewis & Harris, 1990, p.4). Perhaps the first report that left-handed children score lower on tests of "general intelligence" was published by Wilson and Dolan (1931). More recently, Zangwill (1962, cited in Nebes & Briggs, 1974), Berman (1971), and Branch, Milner, and Rasmussen (1964) have reported finding that these "decrements" are limited to mixed-handed individuals, that is, in those individuals who do not have a strong hand preference for performing a variety of unimanual tasks. Branch, Milner, and Rasmussen (1964) argue that "in these persons, language and visuo-spatial skills are not segregated into separate hemispheres the way they are in most people" (p.209). In a large scale study designed to examine the postulated association between Sinistrality and cognitive deficits, Hardyck, Petrinovich, and Goldman (1976) collected data on handedness, social-economic-status (SES) and cognitive abilities data (e.g., Lorge-Thorndike IQ Test, a figure copying test, several subtests of the Stanford 27 Achievement Tests) on 7,688 children in grades 1 to 6. No significant differences were found between left- and right- handed groups across each grade level and SES strata. The authors also provided a summary of 33 studies, most of which also failed to find significant differences between right- and left-handers on various measures of intelligence. Possible Reasons for Discrepancies As we have seen, the literature on hand preference and Visuospatial ability presents a very mixed picture. Depending on the investigation, normal left-handers either do more poorly than right-handers on spatial tasks, are no different from right-handers, or actually surpass right- handers. How might these discrepancies in the literature be resolved? Fluid versus Crystallized Intelligence. One possibility is that the discrepancies could result from inherent differences in the spatial tasks themselves. .For example, Hicks and Beveridge (1978) have criticized the findings of Hardyck et a1. (1976) on the grounds that the lack of significant findings may be due to a sampling error. They predicted that significant differences between handedness groups may be obtainable if the measures selected as dependent variables are chosen with Horn's (1976) definitions of crystallized and fluid intelligence in mind. As discussed previously, particular attention must be paid to individual task demands and to the possibility that 28 higher or lower performance on one type of task might not mean the same thing as similar performance on a separate task requiring different cognitive strategies (e.g., fluid vs. crystallized intelligence) for its solution. Horn (1976) defined fluid intelligence (FI) as a "facility in reasoning, particularly in figural and non-word symbolic materials, as indicated in tests such as letter series, matrices, mazes, figure classifications, and word groupings..." (p.445). Hicks and Beveridge (1978) argue that Hardyck et al. (1976) restricted their analyses to scores obtained on measures of "crystallized intelligence" (CI: Cattell, 1971; Horn, 1976), which test knowledge of previously learned information or automatized skills. Using a measure of F1 and CI (see description of both tests in Hicks and Beveridge, 1978), these investigators studied performance differences on the two types of tests in 37 right-handed and 30 left-handed college students. The groups did not differ on the measure of CI, but the left- handed group scored significantly lower on the test of F1 (p<.02). As mentioned previously, the term "deficit" has been used to characterize relatively lower performance on various cognitive tests among specific subgroups of neurologically normal subjects. Again, the term "deficit" implies a cognitive dysfunction, but, as we have seen here, even where between-groups differences have been found, the scores all fall within the normal range for the tests themselves (e.g., 29 Briggs et al., 1976). Hence, most subgroups of left-handers do not show cognitive deficits per se, but only lower scores in comparison to other handedness groups (or larger discrepencies between their own spatial and verbal scores). Despite this caveat, Annett (1985: cited in Corballis, 1989) argues that those individuals who are homozygous for the RS— allele tend to be more susceptible to reading deficits. In contrast, those who are homozygous for the RS+ allele may be more prone to deficiencies in mathematical ability and possibly in motor-speed skills. Subgroups of Left-Handers. In summary, discrepancies could result from inherent differences in the nature of the spatial tasks themselves (e.g., whether they rely predominantly on FI or Cl intellectual processes for their correct solution). Another possibility is that the discrepancies reflect sampling error arising from the generally greater heterogeneity of left-handers in cerebral organization and in cognitive ability, so that any given sample of non-right-handers might include a different mix of different subgroups, or phenotypes, of adextrals. Some support for this possibility has been presented by Kimura and D'Amico (1989). These investigators administered cognitive tests and a verbal dichotic listening task to both adextral and dextral students recruited from programs that (presumably) are either spatially demanding (e.g., engineering, visual arts) or that (presumably) do not require high spatial ability (e.g., English, philosophy). 30 The cognitive tests included a hidden figures task, paper- folding, cube comparisons, and card rotations, as well as tests of "general reasoning ability," perceptual speed, and vocabulary. A dextral was defined as anyone who reported using the right hand on at least 7 of 8 hand-use tasks. All other subjects were classified as adextrals. The result was that when the scores were collapsed across group (program of study), dextrals outperformed adextrals. The difference, however, was predominantly between the dextrals and adextrals in the non-science group (p<.005). In the science group, dextrals and adextrals performed at comparably high levels (p=.ll). Based on further evidence from a dichotic listening task, Kimura and D'Amico (1989) concluded that their sample included at least two groups of adextrals in terms of (language) lateralization patterns. Those adextrals with higher spatial scores within each of the academic major groups showed a right ear advantage (REA) for verbal stimuli on the dichotic listening task, suggesting left hemisphere dominance for language (p<.05). Conversely, adextrals with lesser spatial ability showed a significantly reduced right ear advantage, suggesting a greater degree of right hemisphere dominance for language. The finding that adextrals with poorer spatial ability had a weaker REA and, by implication, a greater measure of mixed-dominanCe for speech and language functions (see Footnote 1) corroborates Levy's (196) original model. 31 Kimura and D'Amico identified their subgroups on the basis of performance on the dichotic listening test. Another possible index of subgroup membership may be in the phenotypic expression of handedness itself. Previously, we have referred to the use of questionnaires for the determination of handedness. The decision rules, however, have not been standardized, and several strategies for creating handedness subgroups have been employed. In their study of college students, Kimura and D'Amico defined a right-hander as anyone who performed at least 7 of 8 hand- use tasks with the right hand. All other subjects were classified as adextrals (non-right-handers).3 This method of grouping subjects by handedness was also used by Witelson (1985) in her study of handedness and corpus callosum size. Another approach is to divide handedness phenotypes into the three categories of pure right-handedness, pure left- handedness, and mixed-handedness. Using this tripartite division, Annett (1967) found that pure left-handedness is relatively rare and that most groups of sinistrals are predominantly mixed-handers. A third approach (e.g., Gutezeit 1982; cited in Peters & Servos, 1989) is to use the categories right-handers, consistent left-handers (CLH) and inconsistent, or weak, left-handers (ILH). Peters and Servos (1989) prefer this classification scheme because "...in a predominantly right-handed world the average left- hander might be expected to prefer the right hand for some activities. A consistent preference for the left hand, in 32 spite of environmental pressure to the contrary, might indicate that the committed left-hander is somewhat disadvantaged with the nonpreferred hand and is, in fact, a person with some degree of pathology" (p. 342). This possibility has been supported where infants (and young children) are concerned (see Harris & Carlson, 1988, p.307). Consistent preference for left hand use in adults likewise perhaps reflects a more benign set of etiological subtrates as well. To test the validity of the distinction between CLH and ILH subgroups, Peters and Servos (1989) administered both unimanual and bimanual motor tests that involve varying degrees of skill, speed, and strength to 53 CLH, 65 ILH, and 57 right-handed (RH) college undergraduates. Each subject was given a 9-item unimanual hand-use questionnaire. All persons who reported (on item #1) using their left hand for writing were classified as left-handed (in this age and social cohort group -- male and female students at a Canadian university), as it was expected that all or nearly all left-handers would write with their left hand. Therefore, a subject who reported using the left hand on 7 of the remaining 8 questions was considered CLH, and a subject who reported using the right hand on any 2 of the 8 remaining items was considered ILH. The subjects then were administered a series of strength and skill tests, including a rapid finger tapping test, a grip strength test (using a hand dynamometer), the Purdue Pegboard Test (a measure of 33 finger-tip dexterity), and a square-tracing test (to evaluate dexterous control of the distal musculature of the upper limbs). On the hand-use questionnaire, the CLH and RH groups produced similar patterns of responses, but in the opposite direction as expected. Contrariwise, the ILH subjects often showed a "dissociation between the writing hand and the hand used for activities requiring strength and skill of whole arm movement" (e.g., throwing a ball). There were no significant differences between the three groups for writing speed. On the grip strength measure, the left hand was consistently found to be the stronger hand for the CLH subjects (p<.025). As expected, the right hand was the stronger hand for the RH subjects (p<.025). There also was some evidence of a sex difference. For the ILH males the right hand was the stronger hand (p<.006), whereas no significant hand difference was found for the ILH females. Thus, although CLH individuals were stronger with the left hand, ILH subjects (at least in the case of males) were stronger with the right hand. On both the rapid finger tapping test and the Purdue Pegboard Test, the preferred hand was faster for all groups (p<.001): the right hand for the right-handers and the left hand for the left-handers, including the ILH group. For the ILH group, then, there seems to be a dissociation between skill (finger tapping) and strength (see above). 34 On the single-hand condition of a square tracing task, both left-hand groups produced "higher quality" tracking performance with the non-preferred hand (p<.001). In the dual-task condition, however, the difference in hand performance between the two hands working simultaneously (tracing two separate squares) was larger in the CLH group than in the ILH group (p<.014). This same difference between hands was also larger for the RH group compared to both the CLH and ILH groups (p<.001). Finally, on a Rhythm Finger Tapping Task, Peters replicated his earlier finding that the RH group is faster than the other groups when required to tap twice with the right hand for every one tap with the left (condition R2/L1) (p<.0001: see Peters, 1987). The ILH group out-performed the CLH group for this same combination (p<.013), but the CLH group showed a non-significant trend towards better performance than the ILH group with the reverse (L2/R1) tapping combination. In summary, whereas the ILH group showed greater grip strength with the right hand, the CLH group was stronger with the left hand. This means that in a study of grip strength that failed to differentiate these two subgroups of left-handers, these opposing trends would cancel each other out, leaving the impression of no net difference between hand strength for adextrals (see Peters, 1983). Secondly, although the ILH group showed a smaller between-hand difference than the CLH group on the tapping, Purdue pegs, 35 and square tracing tests, both groups differed reliably from the RH group in that they consistently performed better with the left hand. The CLH and ILH groups differed significantly, however, on the 2:1 Rhythm Finger Tapping Test. Finally, although the ILH subjects reported being strongly left-handed for activities such as writing, they also reported some right-hand use (as opposed to the CLH group) for other tasks that involved the use of the more proximal, larger muScle groups controlling arm movement (e.g., throwing a ball, using a racquet). In summarizing their results, Peters and Servos (1989) warn that if distinctions between ILH and CLH groups are not made in performance studies, misleading statements about the nature of left-handedness are inevitable. Hence, any global statements about performance differences between left- handers and right-handers are "premature." Unfortunately, this warning does not bode well for most studies of handedness published during the last few decades. Peters and Servos (1989) discuss the significance of the demarcation of an ILH subgroup on the identification of the underlying mechanisms of handedness. For example, it may be that the developing lateralization processes that are consistent in CLH's and RH's proceed in an unusual pattern in ILH's. Peters (1983) suggests that in the developing, lateralized motor system, attentional and structural systems develop separately but in concert with each other. For instance, he notes that attentional lateral biases towards 36 the right in dextrals are evident before the pyramidal tracts that are used to guide skilled volitional movement are structurally mature. It may be, then, that in ILH's the directional biases of the structural and attentional processes are not equivalent. If so, certain motor tasks that rely to different extents on attentional versus structural systems for their completion may favor different hands in the ILH group (e.g., handwriting, which requires highly focused attention, versus throwing a ball, which relies on more basic attentional processes) (see Peters, 1987). Because these two subgroups of left-handers differ on motor tests that require attentional processes to varying extents, the possibility arises that further differences between subgroups of left-handers might be observed on measures of verbal, spatial, and/or manual praxis abilities. Handedness and Manual Praxis Different subgroups of adextrals may display not only different patterns for strength of hand preference (Peters, 1989) or lateralization of attention (Peters, 1987) but possibly for the control of manual praxis as well (Kimura, 1983). By praxis we mean the ability to plan and/or execute coordinated movements that may or may not be task specific (e.g., buttoning a shirt). Although the neuroanatomical control of praxis is still not well understood, disorders of praxic movement (the apraxias) are typically the result of left-sided unilateral cortical damage with occasional lesion 37 of the corpus callosum (e.g., Liepmann, 1900; cited in Harrington, 1987, pp. 154-164). This finding implicates certain structural components of the left hemisphere as playing an "executive" role in the voluntary control of motor function for both sides of the body. Furthermore, certain lesions in the corpus callosum, in the absence of any other cortical damage, seem to cause left-sided dyspraxia by depriving the right hemisphere's "hand-center" (part of the pre-central motor strip) of input from the left hemisphere's control of praxis (Liepmann, 1905; cited in Harrington, 1987, pp. 136-165). Liepmann detailed his classification of the separate apraxic syndromes (i.e., limb-kinetic, ideomotor, and ideational) and their neuroanatomical correlates, all of which implicated several portions of the left occipital-parietal region as being responsible for bilateral praxis. The same evidence also showed that lesions of the corpus callosum would lead to left-hand dyspraxia in the absence of left parietal insult. New evidence also suggests that different parts of the corpus callosum mediate different forms of praxis. For example, Gersh and Damasio (1981) have described two cases that support the conclusion that frontal-to-frontal pathways located in the anterior half of the corpus callosum support interhemispheric pathways for coordinated hand-use but not for writing. Gersh and Damasio (1981) conclude that despite the early reports of a pure motor apraxia and agraphia of 38 the left hand occurring together following lesion of the corpus callosum, these two clinical syndromes occur as a result of anterior versus posterior damage to the corpus .callosum, respectively. The repeated finding that the "center" for the control of manual praxis is located in the left hemisphere leads to several questions. For example, why are the centers for the control of speech and praxis typically located in the same hemisphere? The seemingly unilateral control for speech and praxis may indicate that speech production, inasmuch as it requires the coordination of large numbers of muscle groups in sequence, relies heavily on praxis, and that Broca's area may be a repository for memory programs necessary for producing these motor sequences (for discussion, see Kimura, 1983a). The close association between manual praxis and speech is evidenced by the fact that the primary motor area for the right hand and Broca's area are anatomically close, and that speech and right hand movements are often precisely synchronized (Kimura, 1988). Despite the close association between manual praxis and speech, this neuroanatomical conjunction between functions is not invariable. Kimura (1983b) presents data on 520 patients with unilateral cortical damage in which the 48 patients, each either left-handed or mixed-handed, showed evidence for more bilateral organization of manual praxis. Specifically, praxis was less affected by left-hemisphere damage and showed a trend to be more affected by right- 39 hemisphere damage in left-handers but not in the mixed- handers. It should be noted that none of Kimura's adextral patients were rendered aphasic by lesions in the right hemisphere. Because Kimura (1983b) separated her patients into only two groups on the basis of handedness questionnaire data (i.e., consistent right-handers versus all others), the question remains open as to whether there is a subgroup of adextral individuals who have more bilateral control for manual praxis. If so, the question arises whether these individuals will differ from other subgroups of left-handers on spatial tasks that have a manipulative or construction component in contrast to tasks that are more purely visuoperceptual. It may be that one of Peters and Servos' two sinistral subgroups -- the inconsistent left-handers -- will display more bilateral control for praxis and that this shared control between the hemispheres will enhance performance on visuoconstructive measures. Recall from earlier discussion (p. 12) that the two cerebral hemispheres contribute in different but complementary ways for the completion of several visuoconstructive measures, such as the ROCF or the WAIS—R Block Design test. SEX DIFFERENCES AND VISUOSPATIAL FUNCTIONS In summary, the evidence for handedness—related differences in spatial ability presents a mixed picture, 40 possibly related to uncontrolled variations in the nature of the spatial task and in the composition of handedness groups. The evidence for our second variable, sex differences, is more straightforward and consistent. What it shows is that although males and females do not differ on overall tests of cognitive ability, they do differ in certain cognitive domains. Specifically, during and after adolescence, males typically excel on tests of spatial ability, whereas females do better on tests of verbal skills, in particular those tests requiring fluency or motor production (see reviews by Maccoby & Jacklin, 1974: Harris, 1978; Bryden, 1979; McGlone, 1980). Levy (1972; cited in Johnson & Harley, 1980) has suggested that these sex differences in specific cognitive functions are due to sex differences in patterns of hemispheric asymmetry. Levy predicted that females, like left-handed males, should display poorer spatial abilities because of a weaker lateralization of language functions in these individuals. In support of this prediction, Levy cited the findings of Culver, Tanley, and Eason (1970), who showed that right— as well as left-handed females displayed a greater primary EEG amplitude of evoked responses in the right hemisphere than in the left, an effect that had been found earlier only in left-handed men (Eason, Groves, White, & Ogden, 1967). Numerous other studies have shown weaker hemispheric lateralization in females relative to males, including reports of lesion data (e.g., Lansdell, 1961; 41 McGlone & Kertesz, 1973; Kohn & Dennis, 1974; Novelly & Naugle, 1986), dichotic listening data (e.g., Knox & Kimura, 1970: Lake & Bryden, 1976), tactile learning (Rudel, Denckla, & Spalton, 1974), tachistiscopic data (e.g., Marcel, Katz, & Smith, 1974), and lateral eye movements (Bakan, 1971: cited in Johnson & Harley, 1980). With regard to Visuospatial abilities, Sanders, Soares, and D'Aquila (1982) found a clear sex difference for the accurate completion of two mental rotation tests. Sanders et al. (1982) administered the Card Rotations Test (requiring the identification of simple abstract forms after mental rotation within a 2-dimensional plane) and the more difficult Shepard-Metzler Mental Rotations Test (requiring identification of complex 3-dimensional figures after mental rotation of a design in 3-dimensional space) to 672 female and 359 male undergraduates. The males scored significantly higher than females on both tests (p<.001), with sex accounting for 2% of the variance on the Card Rotation Test, and 16% of the variance on the Shepard/Metzler Test. Thus, as the difficulty of the mental rotation task increased, so did the sex difference. Ben-Chaim, Lappan, and Houang (1986) found a similar sex difference for the mental rotation of 3-dimensional block designs in large samples of grade school students. On a similar task (Stafford Identical Blocks Test: Stafford, 1961), Marino and McKeever (1989) also found a significant sex effect in college Students. It is important to note that in all such 42 comparisons, between-sex differences typically are less than within-sex differences. There also is some evidence that at least one subgroup of women, namely right-handers with a history of familial Sinistrality and who rate themselves high in spatial experiences, are among those achieving high scores on tests of spatial ability (Casey and Brabeck, 1990). Kingsberg, LaBarba, and Bowers (1987) have provided some support for the hypothesis that there are sex differences in patterns of cortical organization for cognitive functions. Using a dual-task paradigm with block design (a visuo-constructive task) during concurrent right- or left-hand finger tapping, they found that both men and women display similar lateralization patterns for the visuo- constructive processing of the block designs across two levels of difficulty. However, when a concurrent vocalization task was used instead of finger tapping, for the more difficult block designs, only the females showed a significant interference effect (p<.01). The evidence thus repeatedly shows sex differences in Visuospatial ability. It also shows that the size of the difference depends partially on the nature of the task. In a meta-analytic study, Linn and Petersen (1986) found a large male advantage on tests of mental rotation (of 2- and 3-dimensional figures), a smaller male advantage on tests of Spatial perception (e.g., the Rod and Frame Test), and a ‘Weak difference on tests of spatial visualization, such as 43 the Block Design subtest of the WAIS-R. At least two different explanations of these differences are possible. One is that sex differences are smaller on tests that are solvable using both verbal and non-verbal strategies. Another is that the occurrence of sex differences on Visuospatial tests depends on the extent to which the tests draw on visuoperceptual rather than visuoconstructive functions, on the view that visuoperceptual tasks (e.g., Stafford Identical Blocks Test) tend to be less open to the use of linguistic strategies than visuoconstructive tests (e.g., Block Design) for their accurate completion. Kingsberg et al.'s results (1987) suggest that if language functions are more bilaterally distributed in females, females might be more likely to invoke verbal strategies (drawing on greater inter-hemispheric cooperation) in attempting to complete a visuo-constructive task that otherwise is associated with predominantly right- hemisphere activation. If so, one might assume that there would be increased commissural connections between the two sides in order to facilitate interhemispheric coordination of language functions. Conversely, it may be that the neuropsychological control of speech and language functions is not more bilaterally distributed in females at all but only seems to be so because of possibly greater numbers of large diameter axons coursing through commissural connections between the hemispheres, allowing for increased 44 bilateral cortical activation for the completion of both verbal and non-verbal tasks. Neuromorphology and Sex Differences As we have seen, differences between right- and left- handers in strength of lateralization of function seem to fit with the anatomical data at both the cortical and subcortical levels. In the case of sex differences, however, the evidence is either negative or inconclusive. deLacoste-Utamsing and Holloway (1982) reported that the posterior commissural connections (splenium of the corpus callosum) are larger and more bulbous in females than in males. Peters (1988), however, after examining more recent studies, concluded that convincing sex differences in splenial size have not been firmly established (cf. Witelson, 1985, 1989; Kertesz et al., 1987). Peters (1988) also noticed a finding that emerges repeatedly in the literature, namely, that whereas male brains, on average, are larger than female brains, the corpus callosum does not show an allometric relationship consistent with the increased size of the male brain. For example, Kertesz, Polk, Howell, and Black (1987) found no correlation between total callosal cross-section and brain size in 104 subjects. Peters (1988) believes that because are homozygous for handedness (RS+, RS+). For example, in the study cited earlier, Weinstein (1987) found that on the Rey-Osterrieth Complex Figure Test (ROCF), right-handers With FS+ performed more like left-handers than like right- handers with no history of familial Sinistrality (FS-). Namely, right-handers with FS+ and left-handers with a non- ‘(1 0‘ 51 math/science academic major did worse than the other subject groups. Recall that Weinstein tested only females and that this finding has not yet been replicated in a male population. Gilbert (1977) examined FS+ and handedness differences for non-verbal perceptual abilities. The subjects were 64 undergraduates, divided on the basis of a 14-item handedness questionnaire into 4 equal groups ("weak" versus "strong" left-handers, and weak versus strong right-handers). Data were collected on manual dexterity, familial Sinistrality, Object Assembly and Block Design (WAIS), face recognition, and visual half-field reaction times to face and alphanumeric (letters) stimuli (symbolic versus form identity of the target stimulus). The result was that although all subject groups had a comparable left-visual- field bias (70% in each group) on the tachistoscopic task with face stimuli, both left- and right-handers with FS+ had Significantly smaller asymmetries for verbal (letter) Processing than those without familial Sinistrality. There were no differences between groups on the two WAIS subtests 0f visuo-constructive ability (Block Design and Object Assembly). Gilbert concluded that the decreased lateralization for Verbal processing in left-handers, or in FS+ right-handers, Somehow interferes with face processing. This finding is Consistent with Levy's (1969) cognitive crowding hypothesis. 52 In a study of reasoning ability, Briggs, Nebes, and Kinsbourne (1976) examined the interaction of handedness and familial sinistrality in WAIS and Scholastic Aptitude Test (SAT) scores. The subjects were undergraduates organized into 6 handedness groups of 34 subjects each (left, right, and mixed by FS+ or FS-). The left- and mixed-handed undergraduates showed a small but significantly lower full- scale intelligence quotient (FSIQ) than the right-handers (p<.04). There was no difference between the two adextral groups. In addition, in all three groups, FS+ subjects had lower FSIQ scores than FS- subjects. Finally, neither handedness nor FS histories were correlated with any between-group differences on VIQ or PIQ. It should be noted that although a significant between-groups difference on FSIQ was obtained, the range for the mean scores for FSIQ in all three groups was 118.9 to 126.7, placing all groups in the high average range of general intelligence as measured by the WAIS. The lack of significant differences between handedness and familial sinistrality groups on VIQ and PIQ Cluster scores was corroborated in children by Fagan-Dubin (1974) and by Eme, Stone, and Izral (1978), who used the four subtests of the WISC-R (2 from the performance cluster [Block Design and Object Assembly] and 2 from the verbal Cluster [Vocabulary and Similaritiesl). To add to these confusing and contradictory sets of findings, a comparison of 86 adextral subjects separated into subgroups based on strength of handedness and history 53 of familial sinistrality disclosed an orthogonal relationship between FS and combined SAT scores for the strongly left-handed group (p<.01) (Searleman, Herrman, & Coventry, 1984). Specifically, there was a 176-point difference in overall performance on the SAT between the strongly left-handed with FS+ (N=11) and the strongly right- handed with FS- (N=13). The pattern was similar when the verbal and mathematical scores were analyzed separately. In other words, consistent left-handers with FS+ did worse on tests of verbal and mathematical achievement than consistent left-handers with FS-. The studies cited above are contradictory, several finding cognitive differences between Handedness and FS groups, others finding no such differences. In a literature review, Swanson, Kinsbourne, and Horn (1980) caution that the interactive effects of handedness and familial sinistrality on cognitive abilities are extremely complex and that any differences are due in large part to: 1) how Subjects are separated into various subgroups: and 2) the nature of the dependent measures themselves. So far we have explored the relationship between FS and handedness across several cognitive domains. How do these Variables affect cognitive performance? After reviewing the literature, McKeever (1987, p.270) concluded that the common assumption that females are less lateralized for language and Visuospatial functions was not readily replicable. One reason, he suggested, was that in several of the studies O. .- -\~ 54 showing males to be more lateralized for language functions, the finding actually reflects an interaction effect between sex and FS+ (McKeever, Seitz, Hoff, Marino, & Diehl, 1983). In a tachistoscopic object-naming latency test, McKeever and Hoff (1982; cited in McKeever, 1987) found the FS+ by sex interaction to be important for separating language lateralization differences across subject groups. FS- females and FS+ males had smaller right visual field (RVF) superiorities than FS+ females and FS- males. This finding was corroborated by McKeever et al. (1983). The spatial test used was the Stafford Identical Blocks Test (SIBT), a measure of spatial visualization ability. The result was that: 1) males consistently performed better than females (p<.0001): 2) FS+ males performed better than FS- males; and 3) FS- females performed better than FS+ females on the SIBT. McKeever (1987) has not yet proposed an explanation for the FS by sex interaction. fgflnispheric Arousal Style Finally, over and beyond the contributions of sex, handedness, reasoning ability, and familial sinistrality to 1ateralization and cognitive functioning, the possibility arises that individual differences in performance on certain Cognitive tasks also may reflect differences in what may loosely be called "hemispheric arousal style” -- the disposition to rely on one hemisphere over the other for a broad spectrum of cognitive tasks. 55 Kinsbourne (1980) presents an interesting argument that cerebral lateralization for cognitive functions is not due primarily to unique characteristics of each hemisphere but rather to asymmetrical activation throughout life due to asymmetrical brain stem (thalamic) activity. For example, the left hemisphere assumes control for speech not because of "specialized neuronal hardware suited to the purpose," but because it is selectively activated for the initiation of verbal responses by the ipsilateral ventrolateral thalamus (see Ojemann, 1975). Kinsbourne (1980) presents two versions of this model as it would apply to genotypic right-handers and non-right-handers. He maintains that non- right-handers, as a group, are not so highly left-hemisphere lateralized for speech because the brain stem in these individuals is "less laterally polarized," thus leading to greater variation in the extent of differential hemispheric activation for speech. There may be clinical support for this hypothesis. Subirana (1958) found that non-right- handers recover more rapidly from aphasia. In addition, Luria (1970: cited in Levy & Gur, 1980) found that FS+ right-handers (heterozygous genotype for handedness according to Annett's model) are more likely to recover from aphasia following left hemisphere lesions than those with only dextral relatives. Kinsbourne (1980) believes that these clinical findings may be due to the availability of Previously established connections between the "brain stem Selector system" and both halves of the overlying cortex for 56 the adoption of a verbal response set mediated by the non— speech-dominant, residual hemisphere. Levy, Heller, Banich, and Burton (1983) have proposed, as an index of activational style, performance on the Chimeric Faces Test. This test requires the subject to view mirror image face composites, where one-half of each face is smiling, and the other half is frowning. The subject is asked to choose which face composite looks "happier." The rationale for this test is that if a subject consistently chooses the face from each pair that has the "happy side" in one but not the other hemispace, the cortical hemisphere that lies contralateral to that side of space is considered to be more active for the perception of emotion. Even though the two composite faces in each pair are identical mirror-images of each other, subjects typically have no difficulty with this task. Banich (1989b) has found that it shows high test-retest reliability, in that subject responses are consistent across transient mood states induced by drug treatment with either stimulant or depressive pharmacological agents. The basis for supposing that performance on the Chimeric Faces Test is an index of a more generalized "arousal" style comes from further evidence (Levy et al., 1983) that individuals who make a preponderance of LVF (right hemisphere) choices on the Chimeric Faces Test perform better on tasks that (on the basis of independent evidence) require more right hemisphere involvement (e.g., 57 tests of face perception), whereas individuals who make a preponderance of RVF (left hemisphere) choices perform better on "left hemisphere tasks" requiring language skills. Levy and her colleagues have proposed a model that conforms to Peters' (1987) dynamic view of laterality in that attention is seen as the proximate variable driving the laterality effect. By contrast, Kimura and D'Amico's (1989) anatomical connectivity model does not view attention as an important variable underlying lateral specialization. THE CURRENT STUDY In summary, the literature suggests that individual differences in performance on spatial tasks are mediated by a complex interaction of variables, including sex, handedness, hemispheric arousal style, FS, and finally spatial task type. The purpose of the current study was to measure the separate and combined contributions of theSe variables in college students. More specifically, the purpose was to compare the performance of different phenotypic subgroups of left-handers on spatial tasks having a manipulative or constructive component, in contrast to tasks that are purely visuoperceptual, and then to determine whether any such performance differences are affected by sex, FS, and hemispheric arousal style. 58 Differences Between Current Study and Previous Research Like most previous studies of handedness and cognitive differences, a more heterogenous sample was selected than that employed by Lewis and Harris (1990). Rather than restricting the sample to those individuals in the upper 3- 4% of the population with documented evidence of high academic achievement, the subjects were an unselected sample of college undergraduates. This choice was made for two reasons. First, it greatly expanded the pool of eligible subjects, a crucial consideration in light of the relative scarcity of left-handers. Second, it increased the heterogeneity of the subject pool of both right- and left- handers, thereby enhancing the likelihood that different phenotypic subgroups of adextrals would be included. The study also adopted Peters and Servos's (1989) distinction between consistent and inconsistent left-hand dominant individuals. This "levels of handedness" approach comes closer to the recognition that handedness, like the majority of other behavioral variables under psychological study, rests on a continuum from exclusive dextrality to exclusive sinistrality. The study was also designed to address the contributions to spatial performance of FS and hand differences in motor speed (see e.g. McKeever, 1989), and the influences of subjects' choices of fields of academic study that presumably involve more or less spatial skill (Weinstein, 1987). 59 The study also attempted a more fine-grained analysis of each spatial task, recognizing that for any complex task, both hemispheres are involved to varying degrees at different stages of task analysis. For example, whereas Levy (1969) and Miller (1971) used the Block Design subtest of the WAIS-R to test the "crowding" model, thereby implying that the successful completion of this task largely involves right hemisphere activity, more recent evidence shows that performance on Block Design, as well as the other performance subtests of the WAIS-R, can be augmented through verbal strategies (see Kaplan, 1988), which may explain why sex differences on these tasks are weak or non-existent, in contrast to other spatial tasks. The current research therefore included a different mix of spatial tests, including the Rey-Osterreith Complex Figure Task, a visuoconstructive test that, unlike Block Design, appears to draw more heavily on purely spatial skills while preserving the manual component. With regard to spatial tests that do not require a motor response, converging evidence from the clinical and nonclinical literature indicates that tests of mental rotation, tests like the SIBT, are effective measures of right-hemisphere involvement (Corballis and Sergent, 1989). For example, Deutsch, Bourbon, Papanicolaou, and Eisenberg (1988) found marked asymmetries in regional cerebral blood flow, with greater perfusion in the right parietal lobe than in the left hemisphere, during performance of the 60 Shepard-Metzler Mental Rotation Test, corroborating Ratcliff's (1979), and Masure and Benton's (1983) findings that men with right (rather than left) hemisphere lesions make more mental rotation errors. Other data, however, suggest that even mental rotation tests involve left- hemisphere verbal processing strategies (Kee, Bathurst, & Hellige; 1984). In neurologically normal individuals, for instance, there is a great degree of both left- and right- hemisphere alpha suppression on EEG for more difficult mental rotation tasks (Ornstein, Johnstone, Herron, & Swencionis; 1980). This finding implies that spatial stimuli may be verbally encoded and analyzed to a larger extent for difficult spatial tests than for more simple ones. Finally, in light of Levy et al.'s (1983) evidence of consistent lateralized individual differences in hemispheric arousal that are separate from patterns of lateralization of specific cognitive functions, the current study used an estimate of hemispheric arousal style (performance on the free-viewing chimeric faces task) as a covariate in the analyses of variance. In sum, the primary objective was to compare sex and handedness effects on spatial tasks that vary in the extent to which they are likely to incorporate non-verbal strategies as well as manipulospatial ("visuoconstructive") or spatial visualization ("visuoperceptual") abilities for their solution. The prediction is that, like Harshman et 61 al. (1983) and Lewis and Harris (1990), there will be a significant sex by handedness interaction for performance on visuoperceptual tasks. A further, and perhaps different interaction might be found for performance on visuoconstructive tasks. It was difficult to predict the direction of this interaction effect, but the most likely possibility seems to be that the ILH group would perform better on the visuoconstructive measures than the CLH and right-handed subject groups. If, as discussed previously, there is a subgroup of left-handers with more bilateral cortical control for manual praxis (Kimura, 1983), then ILH subjects may be more likely to show this disjunction in left hemisphere dominance for praxis. If so, ILH subjects, in comparison to CLH subjects, should show: 1) a less dramatic between-hand difference for motor speed; and 2) increased performance on visuoconstructive tasks, relative to purely visuoperceptive tests (requiring the use of no motor systems other than those responsible for visual guidance). Summary of Predictions Sex Differences. Consistent with earlier evidence, it was predicted that males would outperform females on all of the spatial tasks but that the difference would be greater on the the mental rotation test (the SIBT) than on the more complex visuoconstructive measure (the ROCF). This result would be consistent with earlier findings (Sanders et al., 1982; Ben-Chiam et al., 1986; and Marino & McKeever, 1989). 62 Handedness Differences. The prediction for handedness is more difficult to make, given the mixed evidence reviewed earlier. If, however, there is a subgroup of left-handers with more bilateral cortical control for manual praxis (Kimura, 1983), and on the assumption that this condition is manifested as an inconsistency of left hand preference, it suggests that the ILH subgroup will do better on the visuoconstructive measures (3D-Drawing Test: ROCF) than the CLH and right-handed subject groups. In contrast, no differences would be expected between the two left-handed subgroups on the more purely visuoperceptual measure (SIBT). Due to the many and varied discrepant findings in the literature comparing left- and right-handers on spatial tests, no prediction was made how either left-handed subgroup would compare against the right-handers on any of the dependent measures. Sex by Handedness Interaction. Finally, in line with previous findings (Harshman et al., 1983: Lewis & Harris, 1990), a significant sex by handedness interaction was predicted for performance on the spatial tests. Because the subjects in the new study, however, were unselected for reasoning ability, in contrast to Lewis and Harris' selection of "high" reasoners exclusively, no explicit prediction was made about the direction of the interaction (see Sanders et al, 1982; Yen, 1975: and Inglis and Lawson, 1982). However, to the extent that college students in general would be more likely to be drawn from the high- than 63 from the low-reasoning end of the distribution, it was expected that the direction of any interaction effect was likely to be in the same direction as that found by Lewis and Harris (1990). METHOD Subjects All subjects were recruited through the Michigan State University Psychology Department undergraduate subject pool. Followings standard procedures for informed consent (explanation of the study and conditions of participation), all subjects agreed to participate. Subjects also received credit in their introductory psychology classes for participation in this study. The experimental design required a minimum of 40 left-handed males, 40 left-handed females, 40 right-handed males, and 40 right-handed females. Subjects were recruited on the basis of self-report of hand- preference, and they were further divided on the basis of post-hoc analysis of their responses to the handedness questionnaire into three groups: right-handers, CLH, and ILH. Although it was difficult to predict the eventual size of each of the left-hand subgroups, Peters and Servos (1989) had obtained roughly equal sample sizes for their CLH and ILH groups without much difficulty. Johnson and Harley (1980) were also able to obtain roughly equal numbers of CLH and ILH subjects in their study of college undergraduates. Because the subject variables FS and hemispheric activational style (predicted by the chimeric faces test) 64 65 were meant to serve as co—variates for many of the statistical analyses of the data, no pre-screening was used for these variables. Materials I. Handedness Tests. Questionnaire Data: Each subject was given Annett's (1967) 11-item inventory of hand preference. A self-report questionnaire was chosen because the evidence indicates that self-ratings and actual hand performance are related (Kozlowski & Bryant, 1977; see discussion by Harris, 1978); The questionnaire packet also included a survey of familial sinistrality, a question about academic major, and several other items that were included in order to collect data for studies other than this one (e.g., a question concerning the hand position used for writing with the dominant hand; see Appendix A). The subjects' scores on the first 9 items of the hand preference questionnaire (the same items used to determine handedness subgroup membership) were summed in order to yield a laterality index (LI) for each subject, with the lowest score (9) indicating exclusive leftehand use, and the highest score (45) indicating exclusive right- hand use. For purposes of separating the left-handed subjects into CLH and ILH subgroups, the questionnaire was scored following the method used by Peters and Servos (1989). 66 Familial Sinistrality: FS was determined on the basis of the subjects' report of hand preferences for their parents and grandparents only. This decision rule was employed because determination of F8 on the basis of reports of hand use by siblings and aunts/uncles risks confounding FS with family size (Bishop, 1983). A subject with either one left—handed biological parent or with two left-handed grandparents was classified as being FS+. Performance Test: Each subject also was given a timed test (60 sec. for each hand) of motor speed. The test consisted of filling in open circles, arranged in a zig-zag pattern (see Appendix A). Each hand was tested twice: the hand used for writing was always tested first, and the hands were alternated between trials. The average number of circles filled in was computed for each hand, providing a measure of manual speed for each hand. II. Chimeric Faces Test. Individual and group differences in hemispheric arousal fkar the judgement of emotion were assessed with the free- ‘Iinewing chimeric faces test. A comparison of results across SVtJJdies and subject populations suggests that this test is a1) externally valid measure of hemispheric arousal for the Perception of emotion in human faces (Harris & Snyder, 19 90). It was included on the hypothesis that individual (ii—fiferences in hemispheric arousal (a dynamic condition that 153 <:onstantly in flux, in response to transient changes in 67 cognitive activity) as indexed by this task, might be a better indication of an individual's real-time analysis of a Visuospatial task than his more enduring pattern of cortical lateralization for Visuospatial functions. This test consisted of 16 pairs of chimeric faces constructed from photographs of faces published by Ekman and Friesen (1975). The only photographs used were of those four models (two men, two women) for whom both "happy" and "sad" expressions were modeled. Each of the two photographs for each model was divided along the midline axis and then re-combined into a composite, or chimeric, face with the happy expression on one side and the sad expression on the other. Each chimera was paired with its mirror image, with the resulting pair of chimeric faces arranged vertically on one page (see Appendix A for example). To control for the position of the chimeric faces comprising each pair, the positions were counterbalanced so that on half the trials, the face with the target emotion to the viewer's left was tzhe top face on half the trials and was the bottom face on tide remaining trials. Two series of eight pairs (original Searies and replication) were bound together into a booklet, IWhich was stapled across the top. Subjects were asked to choose the face composite from eéiczh pair that they judged to be "happier." This test was 11C>tZ timed, but the subjects were encouraged to make their ChOices quickly. This test can be scored as a continuous VaI‘iable, or, using an extreme-groups analysis, by dividing 68 subjects into those displaying either a strong left- or a strong right-arousal style. III. Vocabulary Test (WAIS-R). All subjects were given the vocabulary subtest of the Wechsler Adult Intelligence Scale - Revised (WAIS-R) as a measure of ability on a "crystallized intelligence" test of vocabulary. Although this subtest is always administered individually under normal testing conditions, for the purposes of this study it was adapted for group administration. The test consists of 32 vocabulary words of increasing difficulty. The subjects were told that they had 10 minutes to complete the test and that they were to provide short, concise, and accurate definitions for each word (see Appendix A). All responses were scored according to the instructions provided in the WAIS-R manual (Wechsler, 1981), with the exception that, under group testing conditions, none of the LJSual queries by the examiner were possible. All responses tJmerefore were scored as if, when a query would normally be .irmdicated, the subject failed to respond appropriately to ‘tlaee query. This method of administration and scoring led to a. "modified raw score" for this WAIS-R subtest. Although ‘tlifiese scores cannot be compared with the normative data Provided for the WAIS-R, these methods were applied CoUsistently for the entire subject sample so that any 69 differences between subject subgroups on this measure could be investigated with confidence. IV. Dependent Measures. A list of the three dependent measures is provided in Table 1. Descriptions of the research materials are provided below. Table l. Dependent Measures (See Appendix A for samples of each test.) A. Visuoconstructive (manipulospatial) Tests 1. Rey-Osterrieth Complex Figure Test 2. Three-Dimensional Drawing Test B. Visuoperceptual Test 1. Stafford Identical Blocks Test I‘la. Visuoconstructive Tests. Rey-Osterrieth Complex Figure Task: Each subject was ggjnven the Rey-Osterrieth Complex Figure Task (ROCF; Rey, 1941: see Appendix A). The figure consists of a base .reecrtangle divided into eight equal segments by horizontal 311d! vertical lines that are intersected by two diagonal liiraees. A variety of internal features are placed within this base structure and on the outer configuration of the design. The complexity of this design allows the researcher (Clr‘ clinician) to examine the subject's ability to plan, 70 organize, and assemble complex Visuospatial information (Goodglass and Kaplan, 1983). Testing procedure. The testing procedures were nearly identical to those employed by Weinstein (1987) and Waber and Holmes (1985). The ROCF, enclosed between two pieces of cardboard, was given to each subject, along with five colored pencils, on an 8 x 10 inch piece of blank white cardboard. The use of the different colored pencils allowed the examiner to follow the subject's progress as he/she reproduced the figure during the copy, immediate recall, and delayed recall conditions, as well as to determine whether a line was drawn in a continuous stroke or was divided into segments. Each group of subjects was given oral instructions to copy the design (hidden under the cardboard cover) onto the kalank piece of paper, beginning with the designated colored pnencil. After a 20-second interval the subjects were iristructed to shift to the next pencil. This procedure <:c1ntinued until all of the pencils had been used or until 'tllea subject had completed the design. The pencil-color cxrkier was black, green, blue, orange, and red. All pencils Were placed beside the subject in that order so as to permit quick access to the next pencil to be used. The ROCF was Presented for a total of three minutes. Upon completion of 'tIIEE copy drawings, the stimulus cards and the subjects' dralWings were quickly removed, and each subject was provided ‘Viftli a new piece of 8 x 10 inch blank paper. The subjects 71 were instructed to draw as much of the original design (that they had just finished copying) as they could remember, beginning with the black pencil. The colored pencils were alternated every twenty seconds, following the same procedures as during the copy condition. Following the immediate recall condition, the drawings were removed and the subjects were told that "in a little while" they would have to draw as much of the figure as they could remember. They were then instructed to begin answering the handedness and familial sinistrality questionnaires. Following a 20- 'minute delay period, with an interpolated task (completing the handedness questionnaires), the subjects were given new pieces of blank paper and instructed to reproduce as much of the ROCF as they could remember. The same procedures for alternating the use of the five colored pencils were followed as were used before. Scoring procedures: The total subject sample included £324 individuals who produced 3 ROCF drawings each (copy, irnmediate, and delayed recall conditions), yielding a total CDf’ 672 ROCF drawings. When it was calculated that it would tialce nearly 170 hours to score all of the drawings (based on 311 average of 10 minutes per drawing), the decision was made 'tCD score half (336) of the drawings, chosen at random from each of the three conditions, in order to determine whether theEire were any trends that would warrant proceeding with the rema ining drawings . 72 All 336 randomly-selected drawings from the copy, immediate recall, and delayed recall conditions were scored according to the system described by Waber and Holmes (1985) and also used by Weinstein (1987). The Waber-Holmes system provides for the objective and quantifiable evaluation of organization, production style, and accuracy. All drawings were scored for: 1) the number of accurately placed line segments belonging to the four major components of the structure (base rectangle, main substructure, outer configuration, and internal detail); 2) the number of appropriately placed intersections, including corners; 3) alignment of the segments of the base rectangle, main substructure, and exterior structures; 4) the direction of execution of the drawing; and 5) the "goodness of organization." Certain modifications, however, were made in (order to meet the particular needs of the current study. Tflie procedures were as follows: a. ACCURACY: The design was broken down into the srnérllest line segments possible and each segment was categorized as belonging to one of the four main components CXE the structure: base rectangle, BR (Figure 1A); main Suhstructure, MS (Figure 1B): outer configuration, OC (FVifigure 1C): and, internal detail, ID (Figure 10). A line Segment judged to be present was assigned a score of 1. If absent, it was assigned a score of 0. b. INTERSECTIONS (Figure 1E): All possible lntLersections, including corners, main diagonals contacting 73 corners, the central intersection (diagonals, horizontal and vertical), the left-side interior box (corners and diagonals), the lower left box, the upper right exterior triangle, and the far right exterior triangle, were scored as present (1) or absent (0). c. ALIGNMENTS (Figure 1F): Alignment of segments of the base rectangle and main substructure, as well as of the base rectangle within the exterior structures, was scored as present (1) or absent (0). d. DIRECTION OF EXECUTION: Most subjects were observed to begin each drawing (across all three conditions) by first drawing the base rectangle and then adding the outer features before the internal detail, or vice versa. This is consistent with developmental studies indicating that after age 13 the base rectangle (BR) and main substructure (MS) become increasingly salient as "primary" (Drganizational units: these units are typically copied and rwecalled first, and then the outer and internal details of ‘tlie design are added (Milberg, Hebben, & Kaplan, 1986: Waber & fholmes, 1985, 1986). In this adult group, it also llrLlikely that most persons also would organize their drawings from left-to-right because of their experience with EHHSJIish and its left-to-right directed alphabet. Nevertheless, the possibility occurred that some subjects might begin by drawing one side (left or right) of the figLIre before the other. Color order was used to determine Whether the drawing had been executed from right to left or 74 from left to right, or whether, in the case of a subject who begins a drawing by completing the BR and/or MS first, the rater was unable to determine a clear and consistent direction of execution of the drawing(s). e. ORGANIZATION: In addition to the objective scoring of discrete component features (see above), the designs were rated for ‘goodness of organization.‘ The organization rating was based on a 5-point scale (abstracted from Waber & Homes, 1985: see Table 2) ranging from poor (1) to excellent (5). 75 FIGURE 1(A - F). WABER-HOLMES SCORING SYSTEM FOR THE REY- OSTERRIETH COMPLEX FIGURE TEST. ‘ , j , u I ' (I v , “a p a . a P‘ 449 I I I h r E. F + ® ® I l i LL, F7 %_ Figure 1. A. Base Rectangle (BR)(12 elements): B. Main sub- structure (MS)(13 elements): C. Outer configuration (OC)(27 elements): D. Internal detail (ID)(13 elements): E. Intersections: F. Alignments. Table 2. Level 1: Level II: Level III: Level IV: Level V: 76 Criteria For Five Levels of ROCF Organization Any production not satisfying criteria for Level II. (1) (2) (3) (4) (l) (2) (3) (4) (5) (1) (2) (3) Upper corner of base rectangle & one other corner: Left vertical of base rectangle aligned; Middle vertical of base rectangle aligned; Three of 6 of the following aligned: upper horizontal of base rectangle, middle vertical of base rectangle aligned with upper right cross; middle horizontal of base rectangle aligned with horizontal of external right triangle, right vertical of base rectangle aligned, lower horizontal aligned at middle of base rectangle. Both corners on left side of base rectangle and 1 on right: Two of 3 sides of base rectangle (excluding left side); One of 3 outer configuration structures aligned with main horizontal and vertical: Diagonals of left interior box intersect; Upper right triangle intersects right corner appropriately. All 4 corners of base rectangle; All sides of base rectangle aligned; Two of 3 outer configuration structures aligned with main horizontal and vertical; Main diagonals or horizontal and vertical intersect; Two left corners and one right of left interior box touch base rectangle and main diagonals appropriately. All 3 outer configuration structures aligned with main horizontal and vertical; Diagonals and horizontal and vertical all intersect; All 4 corners of left interior box touch appropriately. 77 All the drawings were scored by two raters following izhe Waber and Holmes protocol. Rater #1 scored 186 (drawings, and rater #2 scored 150 drawings. To insure rweliability, every 25th drawing was scored by the other of tflne original two raters and by a third independent rater (snee Table 3). All three raters were completely blind with renspect to knowledge of subject group membership at all tiJnes while scoring the 336 drawings. For every 25th dranwing, scored by all three raters, the proportion of enutiries for which the three raters agreed was computed. Chmezrall, interrater agreement was 74 percent. Tar>l 0 0’0 0 O O O 0 here -> O O O O O O O O O O O O O O O O O O o O O O O O O O O O O O O O O O O O O 0 O O O O O o O O 0 O O O O O O O O O O O O O O O O O O O o O 0 0 O O O O O O O O O o O O O O O O O o 0 O O O O O o O o O 0 O O 0 o " O O O o o o O O O 0 O O o o o O O o O O O O O o O O O O O O O O O O 0 O O O O O O O O 0 O O O O O O O O O O 0 o O 010 O O 0 O o 0 O O O 0 O O O 0 Which hand did you use? Which hand did you use? (circle one) (circle one) B R L R 166 i Face Stimul tic and Com osite Chime Sad, of Ila , Examrles .93-mks... u... .. as... ..... ,... . ”an? 167 Subject #: ANSWER SHEET FOR FACES PACKET FOR EACH OF THE 16 PAIRS OF FACES IN THE PACKET, WHICH FACE IN EACH PAIR IS HAPPIER? PLEASE CIRCLE THE LETTER CORRESPONDING TO THE FACE IN EACH PAIR THAT YOU CHOOSE TO BE THE HAPPIER FACE. Pair 1: Pair 10: A Pair 2: Pair 11: A Pair 3: Pair 12: A Pair 4: Pair 13: A Pair 5: Pair 14: A Pair 6: Pair 15: A Pair 7: Pair 16: A Pair 8: Pair 168 “ARMY TEST Please provide 911;! and ggguzatg definitions for the 32 vocabulary words listed below. You will have 10 minutes to couplete this test. 1 . WINTER: 3. REPAIR: 4. FABRIC: O. a. n“-.. -O“ --— 5. ASSDIBLE: 10. MUTE: 11 . TERMINATE: 12. mos 13. MIC: N. 15. 16. 17. 18. 19. 20. 22. 23. 24. 25. 27. 169 mum: DESIGVATE: REIMCI'ANT : OBS‘l'RllCl': SANCHJARY : GMPASSIG‘J EVAS IVE : “ms : 28. 29. 30. 31. 32. 170 PLAGIARIZE: (NINCI‘S: BQ‘MBER : AUDAC 103 S : TIRADE: _' -‘ '.'_d E A 13.1- 171 THE REY-OSTERRIETH COMPLEX FIGURE 172 Subject 8: THREE-DIMENSIONAL MAKING TEST This is a line drawing of a SQUARE: By adding extra lines to the drawing. the square can appear to be represented in 'anEE DIMENSIONS. below. Please draw a "three-dimensional" drawing of a square On the following 6 pages you will be provided with a different line drawing on each page. Try to add whatever lines that are necessary in order to make it look like a three-dimensional object. You will be given 30 SECONDS to finish your drawing, and you will be told when to start. PLEASE WAIT FOR THE BCPHUMENTI-R 10 TELL Ya} 10 START. [fl ”D 178 PLEASE DO NOT WRITE IN THIS BOOKLET IDENKTICAI. BLOCKS N? 0342 FORM AA This test is made up of pictures of blocks turned different ways. The block at the left is the reference block and the five blocks to the right are the answer blocks. One of these five blocks is the sane as the reference block except that it has been turned and is seen from a different point of view. The other four blocks could not be obtained by turning the reference block. For Example: .. Block "A" has the same shape as the reference block, but it has been turned as shown in the figure below. Here is another example. II. for each of the 30 items in the test, you are to find which block is the sale as the reference block and blacken the corresponding letter on your answer sheet. If you should get stuck on any iten, skip it and cone hack to it later. This is a tiaed test. You lust wait until you are given the signal to begin. nusrmgmmsrmmmmstn: . m@ , W3 ,0 “005$ @ $6151 53 es ’° t. ,. a mass 28 W’s :9 a was” ,0 use 184 I MWMMIMICALWSTBT mm: For each of the so it- in the test. please find which block is the she as the reference block and circle the correspondim letter on this answer sheet. ' . i) A 2) 3) 4) 5) 8) 7) a) 9) 10) 11) 12) 13) 14) 15) 18) 17) it) is) 20) 21) 22) 23) 24) >>>>>>>>>>>>>>>>>>>>>>>> ID'U'UDDUUUUUUUOUDUDUOUU' OOOOOOOGOOODOOOOGOGGOGGOO UUUUUOUDUUUUUUUUUUUUUUUDU I!MMMMMMMMMMMMMMMMMMMMMNMM 25) Continued on next page... 185 mm sum rut “amen. am: 11:31 (continual) 26) 27) 28) 29) F... .1: 11' 30) REFERENCES Akesson, E.J., Dahlgren, W.J., & Hyde, J.B. (1975). 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