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Rogan A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF ARTS Department of Psychology 1983 Copyright by Rita Virginia Rogan 1983 ABSTRACT -HEMISPHERIC SPECIALIZATION AND VISUAL SPATIAL FIRST LANGUAGE: THE LATERALITY PATTERNS OF HEARING PERSONS WHOSE FIRST LANGUAGE WAS AMERICAN SIGN LANGUAGE bY Rita V. Rogan Researchers have used Deaf $5 to evaluate the merits of the theory that left hemisphere advantage (LHA) for language is due to the greater capacity of left to process auditory stimula- tion as complex as speech. Laterality patterns reported in Deaf 85 are different from hearing right handers, but this may be due to how, when and if visual, or auditory language has been ac- quired. This study tests the contribution of visual first lan— guage experience to laterality by comparing hearing persons who learned American Sign Language (ASL) from their Deaf parents, with persons who learned sign later in life; on their ability to correctly identify tachistoscopically presented unilateral English words, static and moving signs, and visual spatial ori— ented lines. Non-signing controls were compared on words and lines for which they showed the expected LHA and RHA respective- 1y. as did late learn signers. Performance of hearing native Signers followed previously reported patterns of Deaf native Signers with: reduced laterality (only a trend toward LHA) for words; LH trend for lines; asymmetry for moving signs and the only significant hemisphere advantage demonstrated by right to Static signs. The late learn signers showed a strong RHA Rita v. Rogan for both sign sets demonstrating that age of acquisition con- tributes to differing lateral processing patterns for this visual spatial language. Both signing groups showed greater overall accuracy than non-signers. Findings suggest the hemi- spheres have potential for comparable processing of material traditionally subserved by the other. Visual first language experience is one of the factors which can influence this potentiation. Other theoretical considerations are discussed including trends supportive of Kimura's hypothesis regarding processing of complex motor movement and gender differences in hemispheric functioning. ii For Michael ”Ni-.8 ACKNOWLEDGMENTS I thought 1 had put off writing this until last in the hope of bringing whatever eloquence I could save to bear on that which mattered most -- an expression of my appreciation. The truth is however, that I realized at some level how inadequate any expres— sion would be in light of my feelings -— left hemisphere often fails right in this way! When hearing of my decision to return full time to graduate work, my parents came speedily to my side to assess my compe- tence, quite certain that 1 had taken leave of my senses. How can 1 find the words to say how much it has mattered to me that they really listened to how important that step was to me and became, along with my sister, Jeanne (who always knew) my stron- gest and most reliable supporters. And however do 1 translate an accounting of the many "free meal for our starving student"s into the warmth of being "with family" that I have felt in the sustained love, laughter and con- cern that my Lansing family, Myrtle Gregg, Bob LaFay and Robbie ‘have given to me? Or, the unfailing ability of my dearest friend, RuSs Dodson, to put even my most bizarre "odd man out" feelings into a normalized "you're going through what every grad student has gone through..." He has been an invaluable tether to the land of the objective. iii It is my hope that this study and whatever work I can con- tinue to contribute, will in some way repay my debt to those who have opened to me the vibrant, rich, often poignant, but never pathetic world of the Deaf: J. B. Davis, "Mr. Deafness", the diplomat who so graciously ushered me in; Carlos, the troubled boy without a language whose world changed from raging rebel to ”Joe Campus" once given Sign, for showing me my task; My friend and mentor, Alan Parnes, who patiently refines my Sign and my sensitivity; The interpreters who gave so generously of their time and thoughts -- to a person they are the most truly unsel- fish group 1 have ever encountered; and specifically to one of their number, Mae Booth, from whose experiences "I know I think differently..." the idea for this study was born. And how indeed could I have accomplished the unique method of this study without the technical skill of Kristin Olin, who out of generous friendship spent the hot summer of '82 singlefra- ming Super 8 mm film, while Francine Brown stood in the hot lights in the Interpreters' black turtle neck sweater, posing carefully measured signs. My appreciation to my Committee for the unflagging, scholar- .ly support of Dr. Al Rabin; the generous pinch hitting of Dr. Norman Abeles who took on this complicated endeavor mid-stream; the methodological know-how of Dr. Tom Carr and finally for the steadying, informed and affirmative support of Dr. Al iv Aniskiewicz, my Chairperson. They gave excitedly and generously of the precious gifts: their thoughts, as did Dr. Chuck Bassos, Dr. JOhn “Ed" Mason and Dr. Joseph Reyher. And finally to my most treasured mentor, Dr. Barry Greenwald I offer my thanks. OVERVIEW "Laterality", "asymmetries in hemispheric function", or "cerebral lateralization of function" are ways of describing the most global assignation of specific functions to areas of the brain; either to the right or the left hemispheres. That such asymmetries exist has been known since the differing effects of damage to the hemispheres were first recorded during the nineteenth century. This paper reviews some of the theories regarding lateralization, as well as findings from clinical and experimental work which sharpen the focus of our still fuzzy understanding of what specialties the hemispheres do develop; their relative abilities to switch, or subserve each other's functions to meet the needs of the organism and the conditions under which such switches might occur. Theories regarding the development of lateralization of function focus primarily on either anatomical differences which are seen to facilitate laterality, or on early expe- riences considered necessary for such specialization to occur. Of the former, the importance of stimulation of the auditory sphere of the left hemisphere is dominant; of the latter, a critical period for lateralization of language figures most prominently for purposes of this discussion. vi Persons born deaf appear to be the natural experimental ground for testing of the anatomical theories, as in deafness, auditory stimulation of the central nervous system does not occur. Most clinical and experimental work with laterality of function in the Deaf is conducted with this in mind. Though this literature is far from conclusive, it appears that deaf persons do lateralize for language functioning, sug- gesting that auditory processing is not necessary to accomplish this end. Closer analysis of this literature however, reveals that deaf persons are significantly LESS lateralized in func- tion than are hearing persons. An understanding of psycho- social; educational and demographic patterns of this popula- tion applied to these findings suggests that language acqui— sition experience during a critical period may be a contribu— ting variable to lateral specialization. A comparison of performance on tasks deSigned to assess hemispheric processing, of the hearing children of deaf parens (who share this unique bilingual acquisition experience with their deaf counterparts); to hearing subjects who have acquired ASL before adulthood, but after age 12; and hearing persons who never learned sign language was conducted. Performance differ- ences resulted in patterns demonstrated previously by Deaf persons with early sign language experience, in both degree vii and direction, permitting the inference that those dif- ferences were the result of the uniqueness of the visual spatial first language experience and later bilingual acquisition phenomena, rather than any a priori anatomi— cal difference. viii TABLE OF CONTENTS Introduction..... .................. . ........... .... ........ ............1 Left Hemisphere Specialization and the Ability of Right Hemisphere to Subserve These ....... ....... ................... 4 Right Hemisphere Specialization and Left Hemisphere's Ability to Subserve These Functions ............................... l3 apThe Effects of Deafness on Laterality of Function ................... l9 Reported Aphasic-like Symptoms in Deaf Persons Following Lateral Cerebral Damage ...... . ........................ 21 Experimental Assessment of Cerebral Specialization in Neurologically Normal Deaf Adults..... ....................... 32 Summary ............................................................. SO Present Study ......... . ................................ ...... ....... ..55 METHOD. ......... . ................................................... 57 Experiment I.... .............. ... ....... .................. ...... ..63 Experiment II ..................................................... 66 Experiment III ......................................... . ........... 69 Experiment IV ..................................................... 72 RESULTS... .................... . ..... . ............................... 75 Experiment I ......................................... .... ......... 80 Experiment II ..................................................... 9O Experiment III .................................................... 92 Experiment IV.. ....................................... . ........... 84 Overall Considerations ............................................ 93 ix DISCUSSION........................... ..... ................. .......... 96 Experiment I.......................................... ....... ......96 Experiment II ................ .................. ..... . ....... . ..... 112 Experiment III............... ....... ...... ........................ 119 Experiment IV ....... . ....... . ............ ...... ................... 106 Overall ........................................................... 125 Related Findings .................................................. 132 CONCLUSION .......................................................... 142 Appendices: A. Socio—Linguistic Aspects of Deafness ............................ 146 ,yB. Communication Modes Available to Deaf Persons ................... 152 C. Subject Recruitment Letter ................ . ..................... 160 D. Subject Information Questionnaire ............................... 162 E. Stimulus Order - Experiment I - Words... ........................ 164 F. Stimulus Order - Experiment II - Static Signs ................... 165 G. Stimulus Order - Experiment III - Moving Signs .................. 166 H. Stimulus Order - Experiment IV - Oriented Lines ................. 167 I. Informed Consent Form ........................................... 168 References ............................................................ 169 TABLE TABLE TABLE TABLE TABLE TABLE List of Tables 1. Summary of Multivariate Anova Applied to the Experimental Data of Groups 1, 2, and 3 on Experiments 1 and IV With 13 Subjects per Group.................................78 2. Summary of T Scores for Differences Between Correlated Means of Hemisphere Correct Re- sponses of Groups I, 2 and 3 on Experiments I, II, III, IV. .................................... 82 3. Summary of Multivariate Analyses Applied to the Experimental Data of Groups I and 2 on Experiments 1, II, III, and IV and Sub- analyses of Experiments I and III..................88 4. Summary of Multivariate Anova Applied Se- parately to the Performance Scores of Groups 1, 2, and 3 Across All Experimental Condi- tions........................................ ...... 95 5. Comparison of Original Analysis of Variance Scores With Those After Removal of Subject 20 From Group 2.... ........ ..........................105 6. Mean Laterality Coefficients Computed on the Correct Identification in Each Hemifield per Groups of Simple Signs and Complex Signs, Both Static and Moving, as Identified by Two Signing Groups of Present Study and Deaf Na- tive Signers of Poizner, Battison and Lane (1979).... ....... ....................... .......... 124 xi LIST OF FIGURES Figure 1. Rightfield/left field ratios of deaf and of hearing subjects' performance to both linguistic and nonlinguistic stimuli from six studies ......................... 34a Figure 2. Mean percentage correct responses to each experimental condition for each group ............................................ 76 Figure 3. Mean percent correct responses of all groups on all four experimental tasks by hemisphere .................................... 89 Figure 4. Right field/left field ratios of hearing native signers (slanted line marks), late learn signers (unfilled bars) and non- sign controls (horizontal lined bars) performance on all four stimulus tasks of linguistic and visuo-spatial material ........ 117 Figure 5. Mean percent correct responses of the hemispheres of each of the three groups across word and line conditions ................. 118 Figure 6. Mean percent correct responses of the hemispheres of each of the signing groups across static and moving sign conditions ...................................... 123. Figure 7. Mean percent correct responses of women (Solid line) and men (broken line) by hemisphere across all four experimental tasks for Group 1, native signers ............... 139 Figure 8. Mean percent correct response of women (solid line), all men (broken men) and men without 85 20 (dotted line) by hemisphere across both word and line tasks for Group 2, late learn signers ........... 140 Figure 9. Mean percent correct response of women (solid line) and men (broken line) by hemisphere across both word and line . tasks by Group 3, non-signing controls .......... 141 xii HEMISPHERIC SPECIALIZATION AS A FUNCTION OF UNIQUE BI-LANGUAGE ACQUISITION: THE LATERALITY PATTERNS OF THE BEARING OFFSPRING OF DEAF PARENTS WHOSE FIRST NATURALLY ACQUIRED LANGUAGE WAS AMERICAN SIGN LANGUAGE Rita V. Rogan Michigan State University ‘Data from studies of neuroanatomy (Geschwind & Levitsky, 1968; Witelson & Pallie, 1973), naturally occurring unilateral brain damage (Geschwind, 1970; Milner, 1971), split brain pa- tients (Gazzaniga, 1970; Gazzaniga & Sperry, 1967), chemical anaesthesia of the brain (Wada & Rasmussen, 1960), and from per- formance of non-brain injured persons on psychological tests (Kimura, 1973; Studdent-Kennedy & Shankweiler, 1970; White, 1972) suggest that the two cerebral hemispheres of man are dif— ferentially specialized for behavioral functions in normal hea- ring persons. Though there is little agreement on exactly how the hemispheres differ, this evidence very strongly suggests that in right handed persons with normal hearing, left hemisphere is Specialized for language and right hemisphere for visuo—spatial functions. (Poizner & Battison, 1980) L Several theories have dominated the efforts to explain laterality. One hypothesis for instance, suggests that the left lateralization of language may be a consequence of han- (jedness, as most persons are right handed. This view explains that due to the greater skill and activity of the dominant hand, its' contralateral (controlling) hemisphere receives more and better sensory input, thereby maximizing its development of language functions (Gazzaniga, 1970). Requiring, as it does, an assumption of a strict association of handedness and language, this view does not account for the fact that approximately 2/3 of left-handers are lateralized in the same way as are right-handers/ (McKeever, Hoemann, Florian and Van Deventer, 1976). C Another theory holds that vocal control asymmetry is somehow (/E_I neurologically connected with left hemisphere specialization of language function. Nottebohm's findings of left neural control for song in songbirds provides at least some support for this view (Nottebohm, 1971; Nottebohm, 1972). Differential effects of cutting the left hypoglossal nerve result, depending on the age of the bird, in an inability to sing in adult male birds, to achievement of a complete pattern of song in a young male who has not yet come into full song.) (Marie, as early as 1922 set the groundwork for yet another 'though related, understanding; that of equipotentiality of the hemispheres to subserve language. By positing a developmental argument that there is a symmetry of inborn centers for speech, motor and vision functions and that humans are not born with, but develop a speech center in the left temporo-parietal region, Ma- rie argued that asymmetry increases at a developmental rate. Yet a fourth hypothesis, also anatomically based, counters this equipotentiality theory and is the result of postmortem work done by Geschwind and Levitsky (1968), and Witelson and Pallie (1973). They studied the planum temporale, (which includes Wer— nicke's area, known to be necessary to normal language pro- cessing) of the left and right hemispheres of 100 adult human brains. They found a significantly greater incidence of larger left hemisphere planum compared to that of right hemisphere. They concluded that this anatomical difference could provide a biological basis for specialization of left hemisphere for lan— guage, left therefore having a greater capacity to process au- ditory stimulation, which may be required for optimal analysis and manipulation of the highly complex input of human language. Recent studies indicate that the anatomical asymmetries are pre- sent in the same ratios in infants and neonates, as well (Wada, Clarke & Hamm, 1975). Lenneberg (1971), in support of the equipotentiality theory however, observed that the assumed association between the fibre architecture and language capacity has not been established. The Substrate composition therefore, may not be linked to behavioral function. Hemispheric equivalence for function then can exist even with asymmetry of structure; left and right being equally good substrates for language. Lenneberg further posits that this eguipotentiality exists up to the age of two. Left Hemisphere Specialization and the Ability of Right Hemisphere to Subserve These Specialties: Evidence in support of equipotentiality of the hemispheres to subserve language has been largely drawn from studies of the effects on language of early lateralized brain damage. If the hemispheres are equal in their potential to subserve language, then left damage should not result in the continued impairment of language; right being capable of taking over this function. In the classic studv bv Cotard (1868) persons who were right hemi- plegic since infancy showed no aphasia as adults though the whole of their left hemisphere had atrophied. However, as Dennis & Whitaker point out in their 1977 review of these issues, "Equi— potentiality postulates equivalence of language skills, not just a lack of aphasic signs in the two infant hemispheres." They prefer to examine the question therefore, in light of whether the two hemispheres are equally at risk for disordered language as a result of cortical damage. Because Lenneberg places the critical age for equipoten- tiality at less than two years, the findings of a studv conducted by Annett (1973) of right and left Infant Hemiplegia, with onset of Symptoms before 13 months, are significant. These results in— dicated that the two hemispheres at this stage of infancy are ”0t eQually prone to a disruption of language by lateralized da- mage, With 32% showing decremental performance after left damage compared to only 10% after right damage. Elaboration of the quality of language impairment resulting from lateralized damage was provided in a study by Dennis & Kohn (1975), which evaluated the syntactic performance of 9 hemide— corticates with onset of infantile hemiplegia before one year of age, who showed no clinical signs of aphasia. Those with a re— maining right hemisphere were slower to respond to passive sen— tences, deficient in discriminating the meaning of passive sen- tences and less accurate in responding to negative than affirma— tive sentences, than those subjects with an intact left hemi- sphere. These findings suggest that what language capacity de- velops in right hemisphere, takes longer and may differ in kind from the linguistic ability which emerges by age 9 in left hemi- sphere. However. the extent to which secondary sequelae to the massive early damage incurred by these subjects. confounds these conclusions and therefore prohibits generalizations to normal brain functioning. must be considered. Findings supportive of a critical age for equipotentiality of the hemispheres in an intact human brain therefore. would be im- portant and are available in the extraordinary unfolding of the life and cognitive development of the feral child, Genie, as studied and reported by Curtis (1977). Though she possesses both hemispheres without known or apparent damage, Genie‘s early Childhood was unique and relevant to this discussion. She had been isolated, immobilized and imprisoned in a spare room in the family home. She was never spoken to, (only “barked" at like a dog by her father when fed) and was punished for making noises with her voice. Presumably. as a result of this linguistic de- privation, when she came to the attention of the authorities at age 13 l/2, Genie only used her voice to whimper. She had not acquired language. Though she was functionally retarded it was judged that she was not etiologically mentally deficient. Her alertness and engagement with persons around her were seen as evidence to rule out Autism. Scores on the Leiter of 4.9 placed her functioning level (With a wide range of scatter) at least as advanced as that of a normal child when s/he would begin to ac— quire language by imitation and spontaneous production of words. Since no evidence of biological deficiency was found, the lin- guistic deficiency was assumed to be due to her unique experience of social and linguistic isolation. Her spontaneous acquisition of language by exposure alone. (once removed from the deprivational environment). coupled with her established right handedness. make the study of her progress an excellent place to examine whether, as Lenneberg (1971) has Posited, a critical period for language acquisition exists. If 50, Genie‘s ability to acquire language should have terminated with the completion of cerebral dominance. Though Lenneberg Placed this time of completion. for language acquisition pur- POSGS, at adolescence, other theorists have argued this closure occurs as early as age 5 (Krashen, 1978). Though other possible variables such as undetected birth trauma, birth defect, early neurological damage are possible influences in this single case, Genie's progress, in primary acquisition of language at her age, offers an excellent opportunity to examine if, and in what way, lateralization and language acquisition are related, without the possible influences of secondary sequelae to early known hemis- pheric damage which blemish the hemidecorticate studies. Genie's continued acquisition of language has been eval— uated for hemispheric processing via dichotic listening tasks Which have reliably shown, over time. a continued left ear (right hemisphere) advantage for words. This was further supported by EEG data during sleep. Genie's RIGHT hemisphere was dominant for processing speech during various levels of language acquisition. Lateralization appeared complete before. and remained stable during, the retarded acquisition of language. While the course of Genie'sacquisition of language by right' hemisphere largely paralleled that of normal first language ac- 9uisition, there were differences. Her progress was much slower. The Quality of language acquired by Genie, also evaluated exten- sively by way of tasks of increasing syntactical complexity. were similar to the observed right hemisphere language phenomenon found in the Dennis & Kohn (1975) group. While she has been able to raster recursion and ordering rules. she has not performed at better than chance levels to tasks involving passive sentences. auxiliary structure and movement rules. In short, those more complex syntactic functions are not within her command. These observations are of language subserved by right hemisphere. in that the EEG measures showed that the right hemisphere of Genie's brain was activated during these linguistic tasks. This suggests therefore, that in the default of left specialization during a time critical for this outcome, right hemisphere will subserve this function, but will do so less competently. While a critical period for left lateralization of language does appear to be sup— ported in this-case, a critical period for language acquisition is suggested only for more complex functions and not for the ac- quisition of simple ordering and recursion. Effects on Lateralization of Bilingual Acquisition Experience (9 Another language acquisition related variable which has been \/ reported to be associated with right hemisphere's participation in language functioning is Bilingualism. While total clarity M g”..- does not exist in this area of neurological/behavioral func— tioning, several factors have emerged as related to cerebral or— ganization for language. First is the order of acquisition. As is the case with other areas of neurological functioning, clini- cal observations of aphasic—like symptoms of left hemisphere damaged persons have formed the foundation of the Bilingual theories.) Ribot's (1881) hypothesis that those languages learned early in the ontogenetic development will be more resistant to impairment following brain damage carries with it the expectation that the first learned language will also be recovered more Quickly. Yet another hypothesis has been developed, that right hemisphere is specialized for second language acquisition in contrast to left hemisphere specialization in first language ac- quisition. Tn an effort to test this hypothesis, Galloway (1980) expected that there should be a higher incidence of right sided lesion in bilingual than monolingual aphasics. She found that indeed 13% right handed (RH) polyglot cases vs. 2% RH monolingual cases, and 58% left handed (LH) polyglot cases vs. 32% LR mo- nolinguals had right sided lesions. ( Experimental studies of the order of acquisition of second language introduce the additional variable of age of acquisition. They are summarized by Vaid & Genesee (1980) as "generally sup- portive of the hypothesis that hemispheric processing of language in early bilinguals resembles the pattern characteristically no- ted in monolinguals, but that late second language (L2) ac- quisition engages the two hemispheres differently." Sussman, et al (1982) report a study which exemplifies the pattern of hemi— spheric specialization characteristic of the bilingual population of this body of literature. Using a verbal-manual competing re- sponse technique, they found that for fluent bilinguals: l. Bilinguals DO lateralize to the left for language; 2. Bilinguals are LESS left lateralized for language than are monolinguals; 3. "Right hemisphere's participation in L2, especially for second languages acquired in adulthood, appears highly likely." 4. "As a group the bilinguals clearly revealed a high degree of variability in hemispheric language repre— sentation compared to the consistent patterns of left hemisphere dominance for the single language of monolinguals." As these were fluent Bilinguals there is no suggestion or evidence of a qualitative deficit in the second language sub— 10 served by right hemisphere in the Bilingual situation. 11 Summary So indeed, right hemisphere, under certain circumstances, has shown an ability to subserve language. We can expect this to occur when: At an early age in the neurological development of the child, right becomes the only intact hemisphere, or A condition of socio-linguistic deprivation exists during the "critical period" for language acquisition prior to adolescence, or A second language, is acquired later in the developmen- tal process: an increase in the likelihood of right hemisphere participation accrues. The quality of language which right hemisphere has been able to Imoduce under the first two of these conditions is simple and does not include the more complex syntactic functions of. which left hemisphere is capable. There is no evidence of this qualitative limitation when the language subserved (L2) followed the natural acquisition of another language; when the individual had acquired a formal language naturally. 12 Right Hemisphere Specialization and Left Hemisphere's ability to Subserve These Functions: What then of right hemisphere's primary specialized func- tions and the potential of left to subserve these? Our discus— sion up until now, not unlike the chronology of the hemispheric literature, has focused primarily on left hemisphere and the function of language. Perhaps because of its newness in evolu- tionary terms, there has been an historical fascination of scientists with language and an assumption of its link with in- telligence (Kinsbourne & Hiscock, 1977). The anatomical struc- tures which underlie verbal utterance are not present in non-human primates (Liebermann, 1968; Liebermann, Klatt & Wilson, 1969). "Thus, man's proud perch atop the highest rung on the phyletic scale-ladder he constructed was solely due to his speak- ing, intelligent 'dominant hemisphere'." (Smith, 1974) No such unique neural architecture characterizes human spatial orienta- tion, as this function is shared with many species on the phylo- genetic scale. It is also a function which "could be regarded as more archaic than language, bilateral before language evolved, and partially crowded out of the left hemisphere by verbal func- tion when it lateralized both in phylogeny and ontogeny." (Kinsbourne, 1974). This coupled with the less obvious nature of deficiencies in visuo-spatial skills, may serve to explain why right hemisphere and its specialized functions, were the subject of less and later theorizing. l3 John Hughlings Jackson was one of the first to consider that an extreme one-sided view of cerebral function with right hemi- sphere positioned as the "minor hemisphere“, was inefficient, suggesting that the posterior lobes of the right hemisphere were the seat of visual ideation or thought; right considered there- fore, the "leading side“ for this function (Jackson, 1958). He reasoned that "If then it should be proven by wider experience that the faculty of expression resides in one hemisphere, there is no absurdity in raising the question as to whether perception - as corresponding opposite - may be seated in the other." This notion was not accepted by the scientific community for nearly a decade. In fact, because by observational methods employed at that time, damage to the right hemisphere produced no apparent language deficits, the prevailing view was that right hemisphere was "stupid space" (Levy, 1981). As was the case with the early evidence of left hemisphere language function, the most striking evidence for specialized right hemisphere function came from clinical observation of per— sons Who had suffered right hemisphere damage. Profound dis- turbances in awareness and orientation were seen. Some were so spatially disoriented that they could not find their way around their own homes. (Springer & Deutsch, 1981) Two major classes of cognitive deficits have been observed in right hemisphere damaged patients. The first is the diffi- l4 culty in perception, manipulation and memory of spatial rela- tionships of objects (to each other and to the individual). Se- condly, a difficulty in perception and memory of visual, auditory and tactile stimulation which are unintegrated, complex and dif— ficult to describe verbally. Other functions with which right hemisphere damaged persons have difficulty are the recognition, perception and memory of: faces, drawings in which a part of the contour is missing, music and nonverbal sounds. (Nebes, 1977) Studies of neurologically normal persons undergoing psy- chological testing are supportive of these observations. They reveal right hemisphere advantages for performance of these same functions. Studies of split brain subjects reveal right hemi— spheric specializations as non—linguistic functions primarily involving spatial processes (Springer & Deutsch, 1981). While there is speculation regarding why right hemisphere seems specialized for these functions, the more relevant ques— tion to this discussion is whether left hemisphere has an equal' ability to subserve them. Kinsbourne's (1974) position, stated earlier, suggests that the traditional right hemisphere skill of spatial orientation was bilateral before language evolved. Perhaps by evolutionary ves- tige then, left hemisphere could have the equal potential to subserve the functions of right. If not equal, then to what de- 15 gree and under what circumstances? Kohn & Dennis (1974) examined the visuo-spatial performances of the same left and right infantile hemiplegic hemidecorticates previously compared on language skills. While there was no sig- nificant difference reflected between right and left hemidecor— ticates in 1.0. scores and tasks involving personal orientation, there were severe impairments of the right hemidecorticate group (Whose only functioning hemisphere was left) on those tasks mea- suring directional sense, orientation and visually guided route finding. In these hemidecorticates, developmental deficits of visuospatial abilities were found, thus leading the authors to observe, "The same capacities evolve to a level normative of considerably higher chronological ages when mediated by an iso— lated right brainhalf." They also noted that even this limited ability of left hemisphere to assume right hemispheric function does not exist when damage occurs in adulthood. The authors conclude that, “either brain half can provide a substrate for at least some of the functions based on analyses of spatial compo- nents. How long such hemispheric equivalence of the immature nervous system persists, is not clear." Another perspective on right hemisphere specialization in the visuo-spatial skills is its capacity to subserve these while also subserving language. This is manifested in the case of Ge— nie (Curtiss, 1977). While performing at her linguistic deve- l6 lopmental level on other normally left hemisphere analytic tasks, this right-handed woman, the product of acute socio-linguistic deprivation, demonstrated an unusual right hemisphere advantage for word processing. Her performance on traditionally right he— misphere visuo-spatial tasks was not only superior, but on some functions, "the highest scores in the literature for children or adults." (Curtiss, 1977) There appears to be therefore, in Genie, a lateralization to the right for both language and non- language functions, and a remarkable superiority of the tradi- tional visuospatial skills in this condition of the absence of language acquisition during a critical period for such acquisi- tion. The superior right hemisphere performance, though not dis- cussed by the authors, is noteworthy in its co—existence with this left hemisphere handicap. The authors did speculate that consistent with the view that right hemisphere is the first to develop due to the greater involvement of perception with envi- ronment, that the amount of visual stimulation received was ade- quate in this case, for right hemisphere development. That which makes her unique is the marked impoverishment of her linguistic and auditory experience during early developmental years. It was concluded that while Genie was likely born with normal left do- minance potential for language, inadequate language stimulation yielded a functional atrophy of the usual language centers of the brain. (Curtiss, 1977) 17 And so we see the emergence of a trifurcation in the expla- natory theories. Is it the importance of auditory processing in a better equipped left hemisphere which affects laterality? Is it, as suggested by Genie, and studies of the effects of second languages, the circumstances of language acquisition? Or is it an interaction between the two? What are the necessary ingre- dient to potentiate left hemisphere language? If the necessary and sufficient basis of left hemisphere specialization resides in stimulation of the greater auditory processing capacity of left hemisphere, it follows then that an exploration of the hemispheric dominance for language and the perceptual functions of persons whose auditory association areas were never stimulated, would be a valuable contribution to our understanding of the usefulness of this theoretical argument. The Deaf are such a population. They are not necessarily without language, however, using a visualmanual language of sign. In some Deaf persons both spoken and visual languages are used. These languages are totally separate, each having a syntax and grammar of its own. Such persons are therefore, Bilingual. There is additional value in the study of this population in that the sign language used by the Deaf displays both complex language structures and complex spatial relations, offering a valuable opportunity for refining our concepts of cerebral asymmetry. 18 The Effects of deafness on Laterality of Function While a body of literature examining the effect of deafness on laterality of function exists, most of it unfortunately lacks certain basic considerations which are necessary to assure the validity of the interpretations made. This is due primarily to the absence of a socio-cultural, clinical knowledge of the Deaf population, on the part of many of the researchers; seasoned though they were in their primary areas of expertise. Such knowledge is necessary to understand and manage the possible contribution of these psychosocial variables of deafness. ln speaking to the importance of this experiential knowledge of the Deaf population in scientific endeavor, and the multiple misin- terpretations that can result without it, Hans Furth (1966) says, "A scientific fact is worthless unless it fits into a framework of comprehensive interpretation.” Understanding of these varia- bles is so very central to the questions posed and the inferences drawn in research with the Deaf population, that it requires a thorough understanding before proceeding.with a review of this particular literature and findings. Appendices A & B have been provided as a thorough discussion of these issues. The reader is requested to read these and use them as reference in sorting through issues which may be confusing and difficult to follow without this information. 19 Summarizing what these Appendices present, we see that in- fluencing variables associated with deafness are: age of onset, severity of hearing loss, use of mechanical aids to hearing, age of first use of hearing aid, deafness of parents, deafness of older siblings, early parent-child mode of communication, mode of communication preferred by the Deaf subject, mode used during research procedure, communication competence of instructor during procedure, competence of the subject in using that mode and fi- nally, consideration of the degree of dependence of a signing mode on English. The Deaf population can contribute much to our understanding of laterality and hemispheric specialization if these variables are understood and considered. The literature on lateral specialization for language in Deaf persons falls primarily into two groups: clinical case studies of aphasic-like symptoms following neurological damage and experimental studies of groups of neurologically normal Deaf subjects. 20 Reports of Aphasic-like Symptoms in Deaf Persons Following Lateral Cerebral Damage: Impairments of language or aphasic-like symptoms, after left hemisphere damage, have led to the inference that the language specialization areas have been damaged and are therefore, in the left hemisphere of the brain. Evidence of this type in the con- genitally Deaf population, is markedly scant, only 16 cases (Grasset, 1896; Critchley,l938; Burr,l905; Leischner,l943; Tur- een, Smolik and Tritt, 1951; Douglass & Richardson, 1959; Sarno, Swisher & Sarno, 1969; Battison, 1979; Kimura, Battison & Lubert, 1976; Underwood & Paulson, 1981) having been reported. The authors of most of these reports stated their intent to evaluate the merits of a statement by Hughlings Jackson (1878). They quote: "Further, the untrained Deaf-mute has his natural system of signs, which to him is of speech value so far as it goes...No doubt by disease of some part of his brain the Deaf-mute might lose his natural system of signs, which are of some speech value to him, but he could not lose speech, having never had it." (Jackson, 1878) That quote is taken out of the context of his discussion of pathologically speechless persons and served to exclude the Deaf from this group, following directly the caveat: "We shall not, for example, deal with those untrained Deaf-mutes who never had speech, but the cases of those 21 persons only who have had it, and lost it by disease... the condition of an untrained Deaf-mute is in very little comparable with that of our arbitrarily taken case of loss of speech. The Deaf-mute's brain is not diseased, but, because he is Deaf it is un-educated so as to serve in speech. Our speechless patient is not Deaf...Moreover, our speechless man retains a service of words which is not speech; untrained Deaf-mutes have no words at all." By this Jackson is neither saying that a Deaf person would not lose whatever speech he did manage to acquire, nor as these authors assume, that his natural sign should be expected to be impaired by damage to the same areas of the brain which, in hearing persons, would result in loss of speech. He was allowing that damage to some area of the Deaf person's brain would result in a loss of natural sign, but did not speculate on its location. He implied a neuro- logical difference between spoken and manual language. Given the time of this conjecture, Jackson's thinking is particularly far-reaching and, given also his acknowledgement of a natural system of signs (implying a separate language), rather informed. How does this small body of literature of reported aphasic- like impairments in Deaf persons who have suffered damage to their left cerebral hemisphere, add to our discussion of the hy— pothesized primary importance of the auditory sphere in the left lateralization of language? If this hypothesis were true, then auditory stimulation (with the complexity of language) would be required for the greater potential of left hemisphere to develop 22 into left lateralization for language. According to Lenneberg (1971) this should take place during the earliest developmental years. Congenital deafness then would be expected to prohibit this linguistic stimulation of the auditory cortex. The likely outcomes in lateral specialization for language in Deaf right handers which would be consistent with the hypothesis then, are either: 1. No dominance for language, which would be observed in language impairment that is less in severity and duration than that observed in hearing left hemisphere damaged aphasics, or 2. Right dominance for language, in which no language impairment would be expected to result from left hemisphere damage. Evidence of language deficit equal in severity and duration to that observed in hearing persons with the same damage would be seen as evidence of left lateralization for language and there- fore, counter to the hypothesis that auditory stimulation is necessary to accomplish this. Though all but one of the reported cases reflect left hemi— sphere damage in what in many cases we are left to assume were right handers, they are not particularly revealing to our under- standing of impact on language. Nearly half of the cases (Burr, 23 1985; Critchley, 1938; Tureen, et a1, 1951; Battison, 1979) were not clearly pre-lingually Deaf and therefore not relevant to our discussion. Of those who were pre—lingually Deafened, problems of missing historical data complicate an understanding of when and how languages were acquired. All cases reported impairments of English based communication modes, but very little, if any damage to independent sign systems. Because there seem to be differing degrees of impairment across these two modes of com- munication, let us evaluate them separately. First, the impairment in functioning in all English BASED modes suggests that the absence of auditory stimulation does not does not result in right hemisphere dominance or specialization for this function. Were that the case, we would expect to see N0 English language impairment. Our ability to generalize beyond this observation would require an analysis of the quality of linguistic impairment on a basis comparable in extent and dura- tion to that seen in hearing aphasics following like neurological damage. This we cannot do for several reasons. 'First, there is a significant amount of variance in execution of manually com- municated language; much more than the variance in pitch, volume & tone of voice in spoken language. Poizner & Battison (1986), phrase the consequent problems encountered in evaluating the linguistic behavior of Deaf aphasics: "how can we define an error in signing, and best arrive at a description of the impairment?“ Secondly, HOemann (1978) reports studies in which an error rate 24 of 42% for written spelling jumps to 78% in the same subjects when using fingerspelling, saying, "This dissimilar performance suggests that fingerspelling is acquired primarily as a means of communicating rather than as a way of spelling English words." Without therefore, a sample of pre-morbid functioning, it becomes impossible to accurately measure impairment. Third, speech of Deaf persons is not comparable to that of hearing persons even when it has been achieved. Written communication and reading is also premorbidly significantly less proficient. Finally, ma— nually expressed English is not directly comparable to spoken English. Overall, these disorders of signed systems which are heavily based on spoken language are not particularly informative due to the fact that the patient's signing is being mediated by spoken language, which is a different language. Similarly, failures in these modes may be due to apraxia for complex motor movements rather than actual impairments of either of the lan- guage systems. These studies therefore are only suggestive of the following patterns: 1. As McKeever (1979) points out in reviewing the re- reported cases of aphasic symptoms in left hemis- phere damaged Deaf persons, "none of these cases was profoundly aphasic even in expression follow- ing relatively short recovery periods." 25 2. Aphasic errors in manual English are of the same type as aphasic errors seen in hearing right-handers so damaged, though less in degree. 3. English based signing modes showed greater impair- ment than ASL. With regard to the impact of left hemisphere damage on in- dependent sign language, these reports described either no im- pairment, or varying degrees of moderate to mild impairment. The absence of more severe sign deficit could be the result of right hemisphere specialization for sign. There are other possible explanations however, which in the absence of better data do not permit our comfortably drawing these conclusions. For instance, the report of this apparent integrity of sign language after left hemisphere damage could be the result of inadequate, or absent measurement of an existing impairment in this manual mode. If the experimenter's knowledge of the breadth of manual language is not tuned, dysfunctional patterns may be overlooked entirely. Where sign impairment is described, we could View it as evidence of left laterality for sign language. However, the im- pairments are much less in severity and duration than seem to be experienced in English based modes in the same patients, sug- gesting greater involvement in sign, of either the intact right hemisphere, or previously unmapped and, in these cases, undamaged areas of left hemisphere. We are unable to speculate 26 beyond this point due to the difficulties in measuring sign be- haviors. however, About independent sign, we can observe with interest that: Left hemisphere damaged Deaf patients all showed con- siderably less impairment in comprehension than in ex— pression; which may at least partially be accounted for by non-linguistic factors of non-linguistic apraxia and/ or use of non-preferred and least practiced hand. All independent sign impairments noted were much less in severity and duration than impairments of English based modes in the same individuals. 27 Summary The clinical measurement, observation and reporting problems produce the major weakness in these reports. Poizner & Battison (1979) Observed, "without adequate linguistic knowledge of the -language their Deaf patients used, these case histories become suspect and unreliable." Another complication in efforts to interpret the language deficits observed rests in the contributions of differential second language processing to aphasic symptoms. Douglass & Richardson (1959) report these are the first to be impaired in bilingual aphasic subjects and the last to be restored. While this bilingual aphasia literature is complex, contradictory and beyond the discussion of this paper, the absence of historical data on these Deaf “aphasics" on when, and how language acquisi- tion developed in these persons, places the possible contribu- tion of second language factors entirely out of the range of measurement and control. While clinical evaluation of this problem is frought with problems of inadequate measurement, confusion of English based manual language with that which is independent of spoken lan- guage, and the confounding of hemispheric specialization for En- glish with that of independent sign, our analyses of these cases reveals several patterns worth noting: 28 There are clear differences between the impact of left hemisphere damage on English dependent and independent sign systems. English dependent modes are affected longer and more severely than independent sign systems, by left damage Deficits in English based modes appear in type to be similar to aphasic symptoms in hearing aphasics. Sign impairments when observed are more often expres- sive than comprehensive and may be due to motor rather than linguistic difficulties. They are also noticeably quick to return. These observations of existing reports of left hemisphere damage in Deaf persons suggest that complete right dominance for language does not result from auditory deprivation and that left lateralization is greater for sign that is dependent on a spoken language than that which is independent of it. Complex auditory stimulation does not appear to be a necessary ingredient for left lateralization for spoken language. Finally, clinical reports as a method of inquiry, however heuristic they may be, suffer in their usefulness in generalize- ability to normal cerebral function. There is the obvious case selection bias of a brain damaged population; these are not neu— rologically normal subjects. There is also difficulty in as- suring the accuracy of site and extent of the lesion itself, as 29 well as in isolating the effects of the injury on blood supply. The brain tends to adjust its work as best it can when damaged. We cannot make assumptions therefore, that functioning in other areas of the brain, post insult to an area, is the same as it was before trauma. Certain of these problems can be eliminated in experimental exploration. Subjects can be matched for multiple variables ra- ther than sharing only the commonality of brain damage. Re— ception and perception can be added to the focus of study, all in a neurologically normal population. Experimental investigation of asymmetries in normal subjects has been carried out in various ways. The objective of investi- gators is to find ways to lateralize inputs—-to present stimuli to only one hemisphere. One of the oldest of these methods takes advantage of the natural split in visual pathways. In humans this split divides our visual world into 2 fields, each of which projects into the hemisphere on the opposite side. If the visual pathway on one side is stimulated (via stimuli in one visual field) for a very short time before conjugate lateral eye move- ment can change the field by scanning (under 200 msec), it allows investigators to compare the abilities of the separately stimu- lated hemispheres. While other methods have been derived, this tachistoscopic presentation seems to be the most frequently used. Classic patterns of cerebral specialization in neurologically 3G normal hearing persons show a right visual field/left hemisphere advantage (LHA) for language stimuli and a left visual field/ right hemisphere advantage (RHA) for faces, geometric shapes, dot localization and other non-linguistic stimuli. (Poizner & Lane, 1982) 31 Experimental Assessment of Cerebral Specialization in Neuro- logically NOrmal Deaf Adults: The experimental literature on the hemispheric functioning of otherwise neurologically normal Deaf persons is sparse. The application of these methods to this population affords an ex- cellent opportunity to investigate laterality patterns for which hypotheses of auditory importance would suggest an absence. While most of this evidence is in one or another way building upon our understanding of the relative merits of the major theo- ries of causality in hemispheric dominance for language and dif- ferential lateral functioning, the actual theories tested in this small body of literature are primarily limited to the effect of anatomical asymmetry vs. an equipotentiality of the hemispheres to subserve language in spite of these anatomical differences. A critical period for language acquisition is not directly ad- dressed or evaluated by these investigators; neither is the pos— sible effect of bilinguality, nor the theory of vocal control. Methodologies used with the Deaf have primarily assessed visual perception with a few measuring tactile and one, amazingly enough, auditory perception via a dichotic listening task (Ling, 1971). Tasks have involved identification and/or matching of uni- or bi—lateral tachistoscopically presented stimuli including words, static signs, moving signs, abstract and concrete pic- tures, non-linguistic designs and dots in matrices. Comparison 32 Groups have been comprised of various combinations of Hearing and Deaf subjects, with wide variation in the matching, description and/or control of subject variables. Because the whole of these studies have been undertaken for the purpose of examining hypotheses regarding the importance of complex auditory stimulation, most have compared groups of Deaf with Hearing subjects. They have interpreted any differences found between groups accordingly, as a function of the absence of auditory stimulation. Only two refer even tangentially to the bi-lingual nature of the experimental situation, or the experi- mental population. None either attempt to control, or incor— porate/evaluate the possible contributions of bilingual factors to their findings. Poizner, Battison & Lane (1979) have attempted to summarize the findings of the major of these studies (McKeever et a1, 1976; Manning et a1, 1977; Neville & Bellugi, 1978; Phippard, 1977; and Poizner & Lane, 1979) by way of right field/left field ratios taken from dependent measures of either accuracy, or speed of responding used by previous experimenters. Using those data, Figure 1 presents the outcome of these major studies. Ratios greater than 1.0 reflect left hemisphere advantages (LHA's); less than 1.0, right hemisphere advantages (RHA's), with asterisks indicating statistically significant field differences. Figure 1 further divides the experimental results by task and stimulus 33 type. Laterality ratios are shown for visual presentation of static ASL sign, ASL moving signs, printed English, static manual alphabet handshapes, and non-linguistic visual patterns. The hatched bars identify ratios of Deaf subjects and open bars those of hearing controls. As to the general patterns which emerge we see the following trends: 1. Deaf and hearing subjects tend to show a LHA for printed English, with much less pronounced asym- metries in the Deaf, often not reaching significance. 2. Deaf and hearing subjects tend to show RHA's to signs presented statically; 3. Manual alphabet handshapes elicit weak RHA, while non— linguistic patterns tend to elicit greater right hemi- sphere involvement. In general then, it appears that, consistent with the cli- nical literature, left lateralization for language is possible without complex auditory stimulation, but that the resulting patterns of hemispheric specialization are different from those in which it is present. Exceptions to these patterns are seen in 34 VISUAL O 63:; a 34.)»: a 0.1.5.... o o alcaaia ....o .30. o r. “S a. . ... I l .r R ...n . . WP . M K .... 01.22.: - a are; a cuzfoa ...: o .3230. u T :1- Onassis nu 1 WA AM .I . -I- - I, n .14.. o 10w.» .1: («5.9. o o O ocuuuvl 3. .... au>uux§ ¢~ J.“ o , 2 ~21; C Inn-TO. 0 8.4; a 102:: .3220. o 4 .234: o 34:52 a KL... “SW 3 .. 01.22.... .- A S .... 22:22.. .0. I > r I at: a «2.3.0. .0 mm Eu 4 a so”: :- (U55; Li p b b b r L b r b b P b r b o o o o o o o I z s a s 6 7 .- 4 S G 7 O 9 I. l. I. L I. L ..., ... U. 5.8.53. 23:33.. :8... 4 ... .. 5.8.53. 2.!!! :3 34a and of hearing subjects' performance to both linguistic and nonlinguistic stimili from six studies. Right field/ left field ratios of deaf (hatched bars) Figure 1. the work of Phippard (1977) and Neville & Bellugi (1978). A re- view of two of the more illustrative studies of this general body of research, as well as one which advances the methodology sig- nificantly and finally, of the two with exceptional findings are appropriate to our discussion. The study conducted by McKeever, Hoemann, Florian and Van Deventer (1976) illustrates most of the issues involved. The authors began their exploration setting their premise as: “left hemispheric language lateralization depends on the inherent superiority of left hemisphere auditory associa- tion cortex, it carries with it the implication that people who have never had auditory language experience would not develop left hemisphere language dominance. On the other hand if the superiority of the left hemisphere in language functions derives from some other anatomical or functional characteristics of the brain, then left hemisphere specia- lization should be unaffected by deafness." (McKeever et al, 1976) Predicated on this assumption a visual processing task was uti— lized for bilaterally presented English words, signed letters, static signs and ASL. Controlling for age, sex and other known handicaps they compared college age Deaf subjects who had learned ASL "before the age of 5", with hearing subjects who were "pro- ficient in ASL". No information was provided on first language. comparability of ASL skills, or the age and method of learning ASL in the hearing Ss, however. No information on age, method of acquisition or competence in English were given for Deaf Ss. Deaf subjects responded in ASL for all stimuli and hearing sub— 35 jects in English. Results showed hearing subjects to have a substantial LHA to uni- and bi-lateral words and a RHA on the ASL task. Deaf 83 showed lateral preferences in the same direction as hearing sub- jects on all tasks. Only unilateral words however, reached sig- nificance for the Deaf, showing LHA. This LHA was significantly less than that shown by the Hearing 85, however. Additionally, hearing Ss showed less right hemisphere capacity for words and less left hemisphere capacity for ASL than did the Deaf. The authors interpreted these findings as "consistent with the pre- diction...that the deprivation of auditory experiences results in markedly reduced asymmetries of cerebral information processing capacities." and "an increased capacity...for 'minor hemisphere' PrOCBSSing...seems indicated for the Deaf." Poizner & Battison (1980) see this conclusion as unwarranted based on several methodological criticisms. First, McKeever et al pooled the scores of ASL signs with that of manual alphabet recognition because the former was so very low. This effectively caused evaluation not for ASL, but for handshapes which are a code for English letters, thereby contaminating ASL with English. Secondly, because only linguistic stimuli were used, no test of general visuo-spatial processing in the Deaf was made to support the authors' conclusions. Finally, the Deaf and Hearing subjects used different response modes, producing results which are not 36 truly comparable. This last point is probably the most obvious indicator of the absence of concern with bilingual factors. The authors set out to test comparatively the processing of two types of lin- guistic stimuli which are in fact also representative of two se- parate languages. Though the response mode of ASL for the Deaf was likely intended as an accommodation to their speech handicap, by allowing the response modes to vary in this way, a confounding occurs. The dependent variable was mediated by one of the lan- guages being tested (ASL) in the experimental group (Deaf), and the other (English) in the control group (Hearing). It is pos— sible for instance that the LHA of the Deaf group to uni lateral words is less than it might be had it been responded to without translation into ASL, a language the authors conclude is in it— self processed with greater right hemisphere involvement. The absence of differences in the bi-lateral (all ASL) task could be explained by many task and strategy variables. Neville & Bellugi (1978) state that their Deaf subjects have reported using a strategy of selectively focusing attention (though not gaze) on one field preferentially for a time, switching back and forth across fields during bilateral presentation. They suggest that this would be a strategy more likely to be used by Deaf persons who customarily receive information by focusing on the signer's eyes, perceiving the signs via peripheral vision. The 37 study by Manning, Goble, Markman & LaBreche (1977) using bila- teral presentation only, resulted in no lateral asymmetries at all in the Deaf. These findings strengthen the explanatory utility of this strategy variable. It would seem therefore, that while this study, as a model of these experimental studies, indicates that Deaf persons do show evidence of lateralization, results are nonetheless incon- clusive. Results could also have been influenced by: 1. Strategy variables unique to the Deaf in bi- lateral presentation, 2. Effects of translation in the use of differing re- sponse modes, 3. Differential cerebral organization for a second language, 4. The absence of stimulation of the auditory sphere 5. The unique visuo-spatial nature of ASL, and 6. Confounding of ASL with English in pooling signed stimuli results. Another study by Poizner & Lane (1979) evaluates more tho- roughly the hemispheric processing of ASL by incorporating as static sign stimuli, signs which in life use do not require movement. This prevents confounding of dominance for ASL with 38 dominance for any reconstruction process which could possibly result from the presentation of one tachistoscopic moment of a totally moving sign context. An additional contribution of this study was its assessment of whether Deaf subjects, seeing a sign and responding by using that sign were processing it as lin- guistic stimuli, or simply identifying its shape. Two subject groups were used: 10 familially Deaf persons who, having Deaf parents, learned ASL as a first language (Deaf group) and 10 hearing persons who were totally unfamiliar with ASL in the other (Hearing group). Each group was measured in their response time to target stimulus identification of 4 types: Arabic numbers, ASL numbers, NOn—ASL handshapes and Geometric shapes known to produce a RHA in hearing persons. Results included a clear RHA for Deaf subjects for signed numbers and a significant LHA for the hearing group in proces- sing Arabic numbers. The interpretation that the Deaf were pro- cessing the stimuli as linguistic material was supported by se- veral items. First, the Deaf reacted much faster (200 msec) to the sign than did the hearing who were unfamiliar with its lin- guistic utility. Second, the Deaf 85 did not respond reliably faster to one sign target than the other, as did the hearing. Poizner & Lane see this as consistent with the view "that Deaf subjects labeled the signs and processed the labels, whereas the hearing subjects relied exclusively on shape cues." Third, the Deaf Ss reacted faster to signs than non-ASL hands, the hearing 39 doing the opposite. Finally, unlike the Deaf, a hearing Ss who showed a large sign asymmetry was likely to show the same asym- metry to non ASL hands, Deaf 83 also showed a RHA for non-ASL handshapes comparable to the Hearing 83. The authors conclude that a RHA for signs in the Deaf im- plies that the spatial processing requirement dominates the lan— guage processing requirements in determining cerebral asymmetry. However, this material is also potentially overlearned. The use of response time for recognition as a measure therefore, may not constitute evidence of linguistic use or incorporation. Finally, only the visuo-spatial task requirements are inferred as causal. Left glaringly unaddressed therefore, is the absence of RHA in the hearing or Deaf groups in processing the geometric shapes: shown in previous studies (Hellige, 1975; Hellige & Cox, 1976) to yield a RHA in hearing subjects. Advancing the methodology in a highly creative way, Poizner Battison, and Lane (1979) introduced the significant variable of motion to the testing of ASL processing by way of a stimulus presentation via 8 mm movie. Three frames were exposed singly to ‘a beginning, middle and end point in the execution of asymmetric signs, totalling 167 msec of animated tachistoscopic exposure per trial. Static signs were also presented as were English words. In the Deaf group were 15 congenitally Deaf adults who learned ASL as a first language and used it as their primary mode of 40 communication. No information on if, when and how English was learned. or competency achieved, is given. Hearing subjects were 8 hearing persons unfamiliar with ASL. While Deaf 58 received all three stimuli sets, hearing re- ceived only English words. Deaf Ss responded to English stimuli by fingerspelling the words, staying in the English based mode. For signs they responded in ASL, also staying within stimuli mode. Hearing 85 showed the expected LHA for English words. The pattern of asymmetry previously seen in the Deaf of an LHA for English words and a reliable RHA to static signs, was obtained, though comparison with Hearing 85 on English words showed less asymmetry by the Deaf. Moving signs were processed with vir- tually equal accuracy across both fields. The highest degree of variability within a group occurred in the Deaf for processing English words. The authors concluded that the LHA for English words in the Deaf "implies that auditory experience is not a necessary con- dition for left hemisphere dominance for words." They allow however, that the segmented output of fingerspelling may have contributed to this LHA. The shift toward LHA, with no real ad- vantage emerging as reliable in processing moving signs is in- terpreted as supportive of the view that left hemisphere func- 41 tions primarily in the analysis of skilled motor sequences and of temporal sequences in normally hearing persons. They grapple with the question, "If our Deaf subjects LHA with English words is the result of left hemisphere specializa- tion for lexical processing, however, why did the same 88 also show a RHA to signs portrayed statically?" They reject the hy- pothesis that two "language centers" exist in each hemisphere of the deaf, one for English and one for ASL, as "unparsimonious" and "unwarranted" because "spatial properties of language can 'mask' left hemisphere linguistic activities.“ Another possible contributor to this outcome not considered by the authors is the bilingual status of the experimental po- pulation. To evaluate this contribution would require infor- mation on when and how English (L2) was acquired for these deaf persons and the degree of competence they had achieved. Such information might relate to the high degree of variability (both marked LHA and RHA in individuaL Ss) shown by the Deaf in pro- ducing the group LHA for words. While not directly addressing the question of Bilinguality Poizner & Battison (1981) reflect the complications involved in interpreting this body of literature due to the "lack of control of the language background of Deaf subjects: clearly ASL signers are needed for research of this sort." I would also add that 42 complete language histories for languages tested, including English, are also necessary. The magnitude of reported influences of bilinguality on he- mispheric functioning make this line of investigation necessary in the Deaf bilingual population, to better evaluate the relative contributions of these factors beyond the presence or absence of auditory stimulation. Kolers (1963) for example has suggested that in bilinguals different languages may have separate memory stores. Hoemann (1978) tested this hypothesis on short term memory in the Deaf using methods which had been successful on spoken language Bi— linguals. He acknowledged that when one language was spoken and the other manual, special considerations exist. For instance, since both languages use different sensory systems they can occur simultaneously. One can speak and sign at the same time. Using static signs, Hoemann concluded that in short term memory Deaf persons do code manual and English stimuli categorically, com- patible with Koler‘s hypothesis. Similarly, a study of long-term memory (Siple, Fischer & Bellugi, 1977) for ASL signs and printed English words led au- thors to conclude "ASL and English are treated as two separate languages in the same way that two oral languages are by fluent Bilinguals." 43 While none of the studies in this relatively small experi- mental body of literature, directly tests the effect of bilin- guality, one study by Phippard (1977) contains enough information fer some of these assumptions to be made. Examining the ques- tion, "would cerebral lateralization of function develop in the absence of language acquisition?" and concerned about whether delayed exposure to language was an impediment to the development of a normal pattern of cerebral differentiation, a comparison of Deaf and Hearing subjects was made. Two Deaf groups were used: one had received exclusively oral training (training in speaking and lipreading English with no use of manual sign), the other received training in Total Communication (the simultaneous use of both manual and oral languages). Because the Oralist Method of educating deaf children prohibits the use of any gestures or sign communication, we may assume that these children would not have been the Deaf children of Deaf parents we have discussed in Ap— pendix A; whose only parent-child language would have been man- ual. The Oralist group therefore would have acquired NO formal language during the 'critiCal period' for language acquisition. The Total Communication group (which combines use of ASL and En- glish) would then be Bilingual, with ASL = L1 and English = L2. Using a matching task of tachistoscopically presented letters and spatially oriented black lines across groups, she found that While the Controls showed the expected LHA for letters, the TC (or Bilingual) group showed only a non-significant Left hemi- 44 sphere trend and the Oral group (No language <5 years) showed a right hemisphere advantage for letters. Spatially oriented lines were processed with the expected RHA in Controls. Oral subjects also showed a RHA, whereas the TC group showed no lateral pre- ference. Fingerspelling stimuli were shown to TC only and no lateral preference was shown, While unfamiliar faces, shown to TC and Control only reflected the expected RHA in Controls and a non-significant Left Hemisphere trend in the TC group. The patterns of visual asymmetries differed from the hearing Controls in both experimental groups. The Oral Group (language deprived) demonstrated greater reliance on right hemisphere for both language and visuo-spatial material. The TC (or bilinguals) demonstrated no significantly greater reliance on either hemi- sphere, though a trend toward left hemisphere strength in letters and face perception was observed. The other study reporting findings uncharacteristic of the previously described laterality patterns of Deaf persons is that of Neville & Bellugi (1978). They first report an earlier study by Neville (1975) in which the lateral functioning of Deaf per- sons was examined to explore the relationship between acquisition of speech and cerebral specialization. In this study 15 normally intelligent, non-speaking Deaf children (9 to 13 years of age) were compared with hearing children of the same age range. Sub- jects were required to identify line drawings of common objects 45 while evoked potentials (EP‘s) were recorded via electroence- phalograph (EEG) from left and right temporal sites. The EP‘s from the right hemisphere were significantly larger than the EP‘s from the left in the Hearing 53. Initial findings showed the laterality pattern characteristic of Deaf Ss in previous studies. with no asymmetry of amplitude or latency of EP components. Behavioral performance was quite similar to the hearing Ss, however. This prompted further analysis of the data which was made by evaluating the EP's of 8 of these Deaf children, the parents of Whom were determined to be deaf. Their first language, learned naturally, was ASL. These 83 DID have asymmetrical EP‘s -- OP- POSITE in direction from the hearing 55, indicating a LHA for the visuo-spatial task. The remaining 7 Deaf children showed no evidence of late- ralization. These children could not speak and did not know sign language. Though they were able to communicate with other people by gesture and pantomime, they had had no experience with formal language such as English or ASL. Summarizing this earlier report Neville & Bellugi (1978) say. "the acquisition of aural—oral speech and language is not the relevant variable in the development of cerebral specializa- tion...Perhaps the acquisition of some formal language is the 46 critical variable in the development of hemispheric specializa- tion for both language and non-language skills." These findings raised however, several questions, most spe- cifically, the apparent left hemisphere specialization for non-language tasks for Which hearing subjects show right hemis- phere specialization. The authors raise two possible explana- tions : l. Deaf persons learn language as do hearing persons, with left hemisphere playing a major role. However, due to the strong visuo-spatial structure of ASL, non— language visuo-spatial tasks are also preferentially performed by left hemisphere, OR 2. Owing to its strong visuo-spatial structure, sign language is acquired with right-hemisphere speciali- zation, leaving left hemisphere to specialize for non—language tasks. Neville & Bellugi (1978) further comment on the need to know more about how linguistic material would be processed by these subgroups of Deaf which differ primarily in early language ex- perience. These authors conducted a second study, in Which there were 14 congenitally Deaf adults (15 to 35 years of age) who were dif- 47 ferent subjects from the previously reported study, Whose major fOrm of communication was ASL. No information is provided on the hearing status of their parents; age and method of acquisition of ASL; competency, age and method of acquisition of English. A language and a non-language task were used. All Deaf subjects participated in the ASL task, but only 8 were given non-language tasks on which eight Hearing controls matched for age and han- dedness were also run. Non language stimuli were dots variably located in a matrix (Levy & Reid, 1976), presented bilaterally and unilaterally to the Deaf and only unilaterally to the hearing (as they found bi-lateral presentation too difficult). Fixation digit was Ara- bic Which was reported before the dot was localized. Instruc- tions were given in written English. The language stimuli of symmetric static line-drawn signs were presented Bi-laterally and unilaterally to the deaf, with signed numbers used as fixation stimuli, which were reported by signed response. The Deaf showed a significant LHA for uni-lateral signs and no lateral difference in bi-lateral presentation. Deaf 83 also showed a significant LHA for unilateral dot presentation, but no difference in bila- teral presentation. Hearing 85 showed a significant RHA for the unilateral dot localization task as expected. The authors suggest four major conclusions to these results: 48 Significant lateral asymmetries in performance indicate that lateral specialization is not de- pendent on auditory stimulation or the acquisition of speech.¥. LHA for sign language indicates it is acquired with left hemisphere specialization like spoken language, even though "it is acquired in the visual-haptic modalities." LHA for dot localization in the Deaf suggests that "since spatial localization is an important aspect of the grammar of sign language, it may be adaptive to grammar of sign language, it may be adaptive to bring bring together these two functions within the same hemisphere." These data suggest that "both biological and experien- tial factors, such as language acquisition and the MODE of language acquisition, interact in determining the functional organization of the brain." (Neville & Bellugi, 1978) 49 Summary Over the course of our discussion we have culled several theories which are considered important to cerebral lateraliza- tion of function, as it is manifest in humans. These are: l. The importance of the auditory sphere of the left hemisphere, 2. The contribution of vocal control asymmetry, 3. Equipotentiality of the hemispheres with a "critical age" for acquisition of language, and a possible variation of this: 4. Order and age of acquisition of first and subse— quent languages may contribute to hemispheric func- tioning. Applying these to this body of research with the Deaf we find that while a tremendous amount of work is still needed for unambiguous patterns to emerge, we can begin to identify those areas which promise the most fruitful avenues of inquiry. First, there is controversy among these experimenters over how best to interpret the patterns of reduced asymmetry found in these studies. Parsimony would suggest however, that the very presence of left hemisphere specialization for language processing in persons Who have never experienced complex auditory 50 stimulation would argue against this being a necessary factor in the emergence of left lateralization. While the potential con- tribution of vocal control has not been amplified by this topic area, the absence of vocalization as a primary mode of expression in this population would suggest that this variable is not a ne- cessary condition for left lateralization for language, either. The reduction in magnitude of asymmetries as well as the high variability within groups of Deaf 55, calls for deeper analysis. Once we look past the deafness as the explanatory variable, the importance of other hypothesized explanations is heigh- tened; specifically, the concept of equipotentiality as viewed through a bilingual framework. The work of Phippard (1977) identifies the comparative out- come of Oral training in language development (likely no formal language during the years of normal language acquisition) as re- sulting in an RHA for language and non-language material alike. This calls to mind the unusual right hemispheric specialization for language and non-language functioning of Genie, in Whom early language deprivation was also experienced. There exists analo- gically a further relationship between the Oral Deaf, Genie and the Left Hemidecorticates reported by Dennis and Kohn (1975), in an inability to reach competence with higher order language functions. (Moores, 1977). 51 This suggests that in cases Where no fermalized language has been acquired during early years of natural language acquisition, left hemisphere defaults to right in specializing for language. The traditional right hemisphere function of visuo/spatial pro- cessing appear to remain in the capacity and specialty of right under these circumstances. Acquisition of either an auditory language, or as suggested by Neville and Belugi (1978), a formal language, then appears to be a developmental experience necessary to the potentiation of a biological predisposition to left hemis- phere specialization for language. The Total Communication Group (a formal language, though not an auditory, acquired first) of Phippard (1977) however, shows a left hemisphere trend for English letters AND facial recognition. A greater number of this group would be expected to be the 18% of Deaf children whose parents are deaf, Who also showed an LHA for visuo/spatial tasks in the Neville (1975) study. These subjects had learned both ASL and English (acquired visually or tactilely -- not auditorily) before adolescence. These findings lead us to our fourth theory of lateral hemispheric processing, the in— fluence of Bilinguality, which has been shown to result in quite similar laterality patterns for the languages involved. While ASL does indeed differ from English in dramatic ways, Lenneberg suggests that differences in languages should not interfere with natural bilingual acquisition: 52 "When language learning is at its biological optimum, namely in childhood, the degree of relatedness between the first and second language is quite irrelevant to the ease of learning that second language. Apparently, dif- ferences in surface structure are ignored and the simi- larity of the generative principles is maximally explored at this age." Lenneberg, (1967), suggesting some validity in the reasoning offered by Neville and Bellugi (1978) that sign would be acquired in much the same way as spoken language; with major left hemisphere involvement. Useful in the development of this body of research would be a clear isolation of the variable of deafness, while focusing on the influence of the unique Bi-language acquisition experiences of these persons on hemispheric processing of English words. Static signs moving signs and visual design stimuli. Of further interest would be the effect on each of these functions of later life acquisition of ASL, as this is the course of ASL acquisition for most Deaf persons, including those Orally trained Deaf Who, past the years of influence of education, find its facility ap- pealing. Of later acquisition of language Lenneberg says, "Most individuals of normal intelligence are able to learn a foreign language after the beginning of their second decade, although the incidence of 'language learning blocks' rapidly increase after puberty. Also automatic acquisiiton from mere exposure to a given language seems to disappear after this age, and foreign languages have to be taught and learned through a conscious and labored effort." Lenneberg (1967) 53 Bilingual literature suggests greater right hemisphere involve- ment with such later acquisition of second language. This could possibly account for the co-existence in previous research of a strong RHA to ASL in some Deaf Se, and an LHA in others: the former possibly having acquired the language later; the latter, earlier. 54 Present Study The current study isolates the unique early Bilingual ex- periences of this Tbtal Communication population from the con- tributions of deafness by investigating the lateral functioning of the Hearing children of Deaf parents Whose first naturally acquired language was ASL. The benefits of working with this speaking. hearing pOpulation spill beyond these design consi- derations into such methodological areas as: the elimination of any hidden independent variable associated with deafness such as attendant undiagnosed neurological differences. If unique laterality patterns are established, a hearing population permits the use of auditory methods as well as standardized written measures in any further correla- tional studies. language competency evaluation is possible and useable with a speaking population. instructional mode, and receptive and expressive language tested may be consistent. For example, spoken responses to word stimuli will control for the possible segmenting influence of fingerspelling. comparable response modes Which permit more controlled and reliable comparison with hearing controls. 55 If no differences in laterality patterns are feund, infe- rences can be made that these unique Bilingual experiences are not contributory to hemispheric specialization of function: sug- gesting that reported differences observed in the Deaf Groups are unrelated to these language acquisition factors and more closely related to the absence of auditory stimulation. In this study therefore the three exact types of stimuli used by Poizner et al (1979) were used; words, ASL static signs, ASL moving signs and a fourth; geometric shapes, was added to assess visuo-spatial skills unrelated to language. Though these stimuli were presented in one session, with order of presentation counterbalanced, for descriptive clarity we will treat them as four separate experimental conditions. Consistent with the methodology developed by Poizner, Bat- tison and Lane (1979), movement was simulated in animation through sequential presentation of still photographs, achieved in single frame exposure of 8 mm. movie film, taken at strategic points during a sign. Stimulus duration was held under latency of eye movement in tachistoscopic method (initially stimulating only one hemisphere) by exposure of only three frames of 8 mm film. 56 METHOD Overall Subjects Group 1 was comprised of 10 hearing adults who are children of Deaf parents and Whose first language, acquired naturally, was American Sign Language. Five of these were first born. There were 7 women and 3 men. Ages ranged from 26 to 58 with a mean of 43.7 years. All were right handed as were their parents, with 2 85 reporting a left handed grand- parent. Mean years of highest grade completed were 15.9, ranging from 12 to 19 years. None had corrected vision less than 20/28. Eight reported having difficulty learning to do math. None reported a history of neurological problems of Epilepsy or blackouts. Group 2 was comprised of 10 Hearing persons whose first language was English and Who acquired ASL as a second language, after the age of 12. Seven were women and three were men. Ages ranged from 18 to 59, with a mean of 35.8 years. All were right handed, only one reported one left handed parent, with none reporting a left handed grand parent Four were first born children. Eight reported having learned another language than sign, one as early as 10 years; all others during secondary education. Education ranged from 57 12 years to 20, with a mean of 16.5 years. NOne reported corrected vision less than 26/20. NOne reported having had problems learning, nor neurological history. Subsequent to participation, one subject told of a history of Epilepsy with non-traumatic onset approximately 9 years of age. The effect of this subject's score will be discussed later. Group 3 was comprised of 10 Hearing controls Whose only language is English and who have no familiarity with ASL. Six women and four men ranged in age from 19 to 47, with mean of 35.7. All were right handed, one reported one left hand- ed parent, none reported left handed grandparents. Only one was first born. Years of education averaged 15.3, ranging from 12 to 26. Four had never learned a second language, two of those who did learn a second language did so naturally in the home, one at age 8. None had corrected vision less than 28/28. None reported learning difficulties or neurological problems. All subjects were recruited by open letter to relevant organizations in the State of Michigan, requesting their participation (see Appendix C). Information was acquired on handedness, age, sex, highest academic level achieved, Grade Point Average, profession, birth order, competency in English and ASL, age and method of acquisi- tion of second language, corrected vision and history of neuro- 58 logical events or conditions in an effort to control for these factors. At the same time Informed Consent was be obtained in writing. (see Appendix D). 59 Stimuli and Apparatus. The methodology used by Poizner et a1 (1979) was used used to the extent possible technologically. A few changes were made in an effort to improve fixation. Therefore, all stimuli were presented on Super 8 mm movie film. Four stimulus sets were used, all exposed by a single frame filming technique and de- scribed separately per Experimental condition. The fixation was controlled by the pseudorandom distribution over one fourth (10) of the trials of each stimulus set, of a fixation image (the "(?)" figures of the Helvetica Press-type Set), Which required identification by the subject When seen. This was a totally nonlinguistic task to offset any possible ef- fects of competing or complementary tasks to the experimental tasks. Subjects were seated and positioned relative to the pro— jected 8 mm image to assure a visual angle of three degrees of. the stimuli center to the left or right of fixation. Distance between fixation point and stimulus; and the distance between Subject and projected image, were varied. For instance, if the subject was seated 76" from the projected surface, then the pro- jected image was adjusted to a fixation/stimulus distance of 4". 60 Procedure. A warning stimulus was presented by the fixation point rapidly pulsating (by repeatedly exposing and covering the lens for two consecutive frames each, While filming the fixation point) for 1 second (a total of 18 frames) before the onset of the stimulus. At stimulus onset either the fixation point re— mained for the duration of the stimulus exposure, or the special fixation image "(?)", appeared for the duration of the stimulus exposure. Subjects were instructed to maintain fix- ation, signal the presence of the special fixation image When present by raising either index finger, and then to report the stimulus. Approximately ten seconds (180 frames of black film) elapsed between trials, with the subject given the time they re- quired to respond to the film. All signed responses were trans- cribed in the notation of Stokoe et a1 (1976), Dictionary of Am- erican Sign Language When there was no rapidly apparent English gloss for the sign. An ASL bilingual, recorded the signed responses. Experimental order was counterbalanced across subjects. Subjects received the following instructions: “You will see a White circle in the center of the screen, like this. It will begin to pulsate, like this. When it does, I want you to focus your attention on it. This design may, or may not, then 60 appear. Ybu must signal When you see this special design by raising either index finger. Do not signal unless you see this design. At the same time, with or without the special design, a picture will appear either to the left or to the right of the circle. YOu must then report the (word, sign, or point) Which appeared on the side. YOu must make this report by (voice, sign, or point). At all times your focus must be concentrated on the circle. There will be no advantage to di- recting your attention to one side or the other. We will do a few practice trials. I will tell you when the actual test begins." Five practice trials were used in Which the special fixation was used twice with stimuli. A minimum of two correct responses on these trials was achieved before proceeding with actual trials; practice trials repeated if necessary. For the actual test trials responses were recorded on the Subject Answer Sheet (See Appendices). 61 Laterality Coefficients (LC) as described by Marshall Caplan & Holmes (1975), considered to be free of overall accuracy le- vels, were computed for all subject scores for each stimulus set. Group mean LC's were used as the dependent measure of hemispheric functioning, with a significance level of .85 selected for all planned comparisons. 62 Experiment I Subjects. Groups 1, 2, and 3. St imuli . Stimulus Set I consisted of the same 20 high frequency three letter English words used by Poizner, et a1 (1979), (all words appeared at least 58 times per million in the Thorndike- Lorge count). These were vertically printed (chart pak Velvet Touch lettering, Helvetica Bold 72 PT/Mlfl772C) to eli— minate the effects of any scanning from left to right that might take place after exposure. Each word was presented for a total exposure of 112 msec, on two frames of film. The words were centered (3 degrees) to the left or right of fixation point and span (.5 degrees) in width and (1.5 degrees) in height. Words used were: JOY, LEG, SKY, ROW, WAY, ALL, ACT, CRY, LOW, PUT, BOW, TEN, OUT, TEA, SUM, PAN, MAP, NOD, RAY, WHO. Procedure. Subjects were instructed verbally in English. They were instructed to respond in English. These words were re- corded on the Subject Answer Sheet under Experiment "Wbrds". Five practice trials preceded the 46 test trials. Re- sponses were scored correct only if the complete exact word was reported by 83. Two of three letters correctly iden- 63 tified were scored as incorrect. Expected Results. It is expected that hearing control monolinguals (Group 3) and late learn signing subjects (Group 2), will show the repor- ted LHA for words, characteristic of right handers. Motivated Hypothesis 1: If, as suggested by earlier studies, early Bilingual ex- perience involving one visuo—spatial language, does affect he- mispheric specialization for the processing of the verbal one of those languages (in this case English), than right visual field (Left Hemisphere) advantage as measured by the mean LC will re- flect less left hemisphere advantage for native signers than that of late learn signers, or non-signing controls. This outcome (Hm: Ml < M2 = M3; LHA) will permit us to reject the null hypo- thesis. Null Hypothesis 1: If early Bilingual experience with a visual spatial first language has NO effect on hemispheric specialization for the processing of one of those languages, then it is expected that all groups will show the same LHA for processing words, as re- flected in no differences between the mean laterality coeffi- cients for Groups 1, 2 and 3. This result (Ho: M1 = M2 = M3) 64 would require acceptance of the null hypothesis. 65 Experiment II Subjects. Groups 1 (native signers) and 2 (late learn signers) Stimuli. Stimuli for Set 11 consisted of the same static signs used by Poizner, et a1 (1979). These were selected as bila— terally symmetric about the midline of the body, so that the arms and hands were equidistant from the fixation point When presented in either visual hemifield. In filming, a fluent Deaf ASL signer was positioned so that the midline of the body appeared (4.4 degrees) from the fixation point When viewed by a subject. Signs spanned approximately (3.8 degrees) in width with the closest edge of the sign (2.5 degrees) from the fixation point. All signs selected had been com- mon ASL signs, "chosen to minimize the transparency of meaning." Facial expressions were neutral and invariant from sign to sign. The signs in the stimulus set did not move in presentation. Three successive frames were shot in the static image for a total of 167 msec. These signs were all pretested by Poizner et al (1979) to be readily identi- fiable without their standard movement. Static signs con- sisted of the following with specific form determined by Poizner et a1 (1979) as referenced in Stokoe et a1 (1965) Where optional variations exist in the language (such spe- '66 cifications appear in parentheses): ASK, AFRAID, WANT, TEACH, HEADACHE, MORE, EQUAL, PLAY, HAVE, LOVE, CONTINUE ("A" hands), RAIN, LICENSE ("L" hands), SELL, MEET, LOOK—AT-ME pl. (i.e., "many people look at me: "4" hands), VACATION ("5" hands on upper chest), CELEBRATE, CAT, MISCHIEVOUS. Procedure. Subjects were instructed in ASL by a fluent Bilingual. They were instructed to respond in sign. These signs were recorded in notation of Stokoe, et a1 (1976) When there was no rapidly apparent English gloss for the sign. Responses were scored correct only if Ss produced the com- plete sign, including appropriate motion. Miming of hand posi- tion alone (usually accompanied by facial/body indicators of "I don't know") were scored incorrect. Expected Results. Motivated Hypothesis II: If the early vs. late acquisition of a visual spatial lan- guage has an effect on hemispheric specialization for the pro- cessing of that language; with Right hemisphere playing a grea- ter role in late acquisition, then it is predicted that the left hemisphere participation of native signers, as measured by the LC 67 of Group I should show greater LHA than that of late learn sig- ners and the RHA should be greater in Group 2 than Group 1. Such an outcome (Hm: M1>M2 as measured by a Left LC, and Hm: M1 Ml, RHA) would permit rejection of the null hypothesis. Motivated Hypothesis IIIa: Further, if ASL with motion added utilizes the processing strategies of both hemispheres in native signers, then RHA=LHA in Group 1. Null Hypothesis III: If age of acquisition of language has no effect on hemi— spheric specialization for processing that language, then the average laterality coefficient for native signers should not dif- fer from that of late learn signers. 7U Null Hypothesis IIIa: Further, if motion in ASL'has no effect on hemis— pheric processing, then these mean LC's would be reflective of the previously reported RHA for processing static signs for both groups. Such resulsts (Ho: M1 = M2; RHA) would re- quire acceptance of the null hypothesis. 71 Experiment IV Subjects. Group 1, 2, 3. Stimuli. Eight renderings of related black lines measuring 7x2.5 mmm and separated by 18 degrees of angle, were used, each exposed for 2 frames (112 msec) and pseudorandomly presented two or three times in each visual field. Recognition of spatial orientation of short lines has been demonstrated to be a minor hemisphere function (Atkinson & Egeth, 1973). Procedure Subjects were instructed in English. A card with all eight stimulus designs was placed in front of the subject Who was instructed to identify the stimulus presented in visual half fields by pointing to the matching design on their response card. All responses were recorded on Subject Answer sheet under "Oriented Lines" with appropriate coding (see Appen- dix H) When the trial items were performed with better than 50% accuracy, the task difficulty was increased by manipulation of room light and/or lens filters Which decreased the figure-ground 72' contrast and sharpness, until 50% accuracy was achieved. Expected Results. It is expected that late learn signers and non-signing con- trols will manifest the RHA previously reported for right handers for processing visual spatial stimuli. Motivated Hypothesis IV: If, as suggested by previous studies, the early experience of acquiring a visuo-haptic language results in the greater use of left hemisphere for processing visuo-spatial stimuli then na— tive signers (having this unique early language acquisition ex- perience) will manifest a mean LC indicating lower right hemi— sphere involvement for visual spatial stimuli than will late learn signers or controls. Another possible outcome supportive of this hypothesis would be a LC indicative of greater LEFT he- misphere involvement for native signers; with late learners and controls reflecting the expected RHA. This result (Hm: Ml < M2 = M3, RHA; and/or Hm: M1 > M2 = M3, LHA) would both permit rejec- tion of the null hypothesis. Null Hypothesis IV: If hemispheric specialization for visuo-spatial tasks is unaffected by early or late acquisition of ASL, then it is ex- 73 pected that all Groups will show the previously reported RHA for visual spatial stimuli as measured by right LC. This result (Ho: M1 = M2 = M3; RHA) would require acceptance of the null hypothe- sis. 74 RESULTS Figure 2 presents the mean percentage correct identification of stimuli by each group on each of the four experimental tasks. Overall accuracy levels ranged from 44% correct by Control subjects (non-signers) responding to words, to 67.5% correct by Group 1 (he native signers) responding to the visuo—spatial sti- muli of Experiment IV. The non-sign using Controls (Group 3) were consistently less accurate than both of the sign competent groups, though this difference did not reach significance (Tables 1 and 3, Main Effect for Group: F(2) = 2.03, p = .1446; F(l) = .01, p = .9438). —-u.~—u—ou—wfl——_———_—~-————_———__—_-————- The experimental design compared all three groups on only two of the experimental conditions (stimulus types), words and oriented lines, and only the two signing groups on all four ex- peri mental tasks. Initial data analyses were conducted sepa- rately, therefore. A summary of all variance analyses is shown in Table l; with three groups on two experiments, and Table 3, with the two signing groups on all four tasks. 75 mpmafiflmucoz . _ .apopm sumo pow counfiocoo Hmucmeapmaufl FR w some on mmmcoamwp upwhoo mwmucoopmm 8mm: .N 6.3me Q mpchMm ””0 i d 80.6 V\\\\\\ 93¢me m>MWMz mug 9..me 8me . H p0 8338 mg 038m 883 3 ea. Hp en E ”ea H ea . . \ . .. V F... V , \ \ . I K m N \ ... m \ \ W\ d... .... a a a K K a... a... i a... mi \ , Hm. ) on. m K E. . am. an. m . m d... m R m S. m. m. w. 76 Experiments I and IV A multivariate analysis of variance was performed first on the hemisphere** correct scores of Groups 1, 2 and 3 on Experi- ments I and IV. Gender was found to have no effect on overall accuracy, nor to interact significantly with the performance of the separate hemispheres on these tasks. There was a significant interaction between Experiment and Gender (F(l) = 7.00, p = .0132), indicating that overall accuracy of men was affected differently by stimulus type, than was overall accuracy for wo- men. fect for Groups, in the overall analysis, indicating that the subjects' overall accuracy levels were comparable in response to words and oriented lines. Thus, differences between the groups in patterns of hemisphere correct scores cannot be attri- buted to differences in overall processing ability. ** For purposes of consistency and in an effort to avoid the usual right/left, field/hemisphere confusion inherent in verbal descriptions of this research area, all references to lateral performance will incorporate the inference of contralateral function which is an assumption of the methodology. RVF will be referred to as Left Hemisphere and LVF, as Right Hemisphere. 77 TABLE 1 Summary of Multivariate Anova Applied to the Experimental Data of Groups 1, I and IV With 10 Subjects per Group. 2 and 3 on Experiments df F p Multivariate Main Effect (Gender) 1 .24 .6307 Multivariate Main Effect (Group) 2 2.08 .1446 Multivariate Main Effect (Experiment) 1 7.41 .0112* Multivariate Interaction Exp X Hemi 1 14.82 .0007** Multivariate Interaction Exp X Hemi X Grp 2 5.13 .0130* Univariate G X H Interactions and Simple Effects: Experiment I (G X H) Univariate Main Effect (Group) 2 1.50 .2407 Univariate Main Effect (Hemi) 1 11.03 .0026** Univariate Interaction (G X H) 2 1.47 .2470 Experiment IV (G X H) Univariate Main Effect (Group) 2 1.72 .1988 Univariate Main Effect (Hemi) l 9.16 .0054* Univariate Interaction (G X H) 2 6.07 .0067** 78 While the three groups did not differ in overall accuracy across tasks, the two Experiments did (Main Effect for Experi- ment: F(l) = 7.41, p = .0112) with greater accuracy of response reflected in higher mean percent correct responses to the oriented lines of Experiment IV. There was a significant interaction effect of Experiment with Hemisphere scores (F(l) = 14.82, p <.001), indicating that the hemispheres performed differently with each experiment. And most importantly, the test of whether there was an interaction between Experiment, Hemisphere and Group was significant (F(3) = 3.63, p <.05), indicating that stimulus type played a role in the varying performances of the hemispheres of each of the groups. 79 Experiment I Because this Experiment X Hemisphere X Group interaction was demonstrated, further subanalyses were conducted on the hemi- sphere correct scores of the three groups on Experiment I (words) alone. There was not a significant Main Effect for Group, indi- cating no reliable difference in overall accuracy scores from one group to the next. There was a highly significant Main Effect for Hemisphere however (F(l) = 37.50, p <.001) suggesting that one hemisphere performed consistently better for all subjects in processing words. Because a Left Hemisphere Advantage (LHA) was expected in Groups 2 and 3, T Tests for Correlated Means were performed to compare left and right hemisphere performance within all groups on Experiment I. Table 2 provides a summary of these scores. On Experiment I difference scores for all goups were in the direc- tion of left hemisphere superiority in performance (as reflected by positive difference scores), with only Group 3 (Control) reaching the expected significance (T(9) = 3.12, p = .012). Fi- gure 3 visually arrays the relative proportion of hemisphere correct responses for each of the three groups on both Experim- 80 ents I (words) and IV (lines) reflecting the consistent though somewhat varying left hemisphere superiority for the word sti- muli. Though in the direction of left hemisphere superiority, the difference score for Group I was very small and, as was ex- pected, it did not reach significance (diff = .400, T(9) = .67, p = .522), indicating that while a slight left hemisphere advan- tage was reflected, this was a small difference. Planned Laterality Coefficients were computed for all sub- jects and using the mean LC as the dependent measure, T Test com— parisons were made of the performance of the three groups in pro- cessing words. As was expected, Groups 2 and 3 did not differ significantly in hemisphere correct scores to Experiment I, and could therefore be averaged for further analyses. Comparing these to Group 1 (native signers) produced insignificant dif- ferences (T(28) = —1.11, NS). Planned comparison of Group 1 and Group 3 only, resulted in a difference between groups that did not reach significance (T(18) —l.46, p = .162). While this was not sufficient to reject the null hypothesis: that the unique bilanguage experience of a visuo-spatial first language, natural- ly acquired, has no effect on the hemispheric processing of Eng- lish, there was nonetheless a discernible difference between the groups. The author's curiosity therefore, combined with the opinion of Hardyck, "..the process of reporting data in terms of statistically significant differences does more to obfuscate and obscure knowledge than any other process. Statistically signi- 81 TABLE 2 Summary of T Scores for Differences Between Correlated Means of Hemisphere Correct Responses of Groups 1,2 and 3 on Experiments 1, II, III, IV Mean SD Diff SD Corr 2Tp T df 2Tp Exp. I Grp 1 LHC 11.0 3.05 RHC 10.6 3.53 .40 1.89 .844 .002 .67 9 .522 2 LHC 11.7 3.89 RHC 9.9 3.21 1.80 2.93 .673 .033 1.94 9 .085* 3 LHC 9.8 2.48 RHC 7.7 3.30 2.10 2.13 .764 .010 3.12 9 .012* Exp. 11 Grp 1 LHC 8.5 2.59 RHC 9.6 2.91 -l.l0 .99 .941 .000 —3.50 9 .007* Grp 2 LHC 7.8 2.74 RHC 10.6 2.27 ~2.80 1.75 .771 .009 -5.06 9 .001* Exp III Grp l LHC 10 2.86 RHC 10.4 2.87 — .40 1.43 .876 .001 — .88 9 .399 Grp 2 LHC 9.8 2.93 RHC 11.8 2.82 -2.0 2.53 .612 .060 -2.49 9 .034* Exp IV Grp l LHC 13.9 2.85 RHC 13 3.46 .90 2.28 .755 .012 1.25 9 .244 2 LHC 11.2 4.23 RHC 13.8 5.67 -2.60 3.40 .802 .005 -2.41 9 .039* 3 LHC 8.7 4.73 RHC 11.3 5.33 —2.60 1.83 .940 .000 —4.47 9 .002* 82 ficant differences, especially in relation to within subject ex- periments are probably the ideal way to obscure meanings of re- sults, a condition that is only exacerbated by journal practices of publishing only p values.", prompted a qualitative evaluation of the data. Post-hoc comparisons were conducted therefore, Which would provide additional information on just how the individual he— mispheres of the groups compared in their separate performances. While the left hemispheres of both native signers (Group 1) and non signers (Group 3) were comparable in their processing ability of words (T(18) =.96, p=.348), the right hemispheres differed in a way which approached significance (T(18) =l.90, p =.074), with the mean percent of correct responses non-signers of .3850 and of native signers of .5300. This difference did not exist between the two signing groups however, with both right (T(18) = .46, p = .649) and left hemispheres (T(18) = -.45, p = .660) of each group performing with comparable accuracy. This suggests that the way in which signers tend toward reduced laterality for pro- cessing words is in a greater capacity of the right hemisphere accuracy rather than a lessened capacity of either hemisphere, When compared to non-signers. This additional capacity of right hemisphere tends to be the strongest for the native signers. 83 Experiment IV While the subanalyses of all groups“ responses to Experiment IV (oriented lines) shows no overall difference in accuracy (Main Effect for Group), a highly significant difference in accuracy of the separate hemispheres was found (F(l) =9.16, p = .0054). Further, an interaction of Group X Hemisphere was significant (F (2) =6.07, p = .0067), indicating that oriented lines were responded to differently by the hemispheres of each group. T scores for correlated means (Table 2) show these dif- ferences to be significant within Groups II (late acquisition of sign), (Tcorr(9) = -2.41, p = .039) and 3 (non-signers) (Tcorr (9) = -4.47, p=.002), with their actual difference in mean scores being equal and in the same direction of greater accuracy (-2.60) by, as predicted, the right hemisphere. While the difference score of Group 1 (native signers) was not significant (Tcorr(9) sl.25, p=.244), it was in the OPPOSITE direction(+.90), sug- gesting native signers have a someWhat more accurate left hemis- phere in this visuo-spatial task. Comparisons using Laterality Coefficients for each subject as the dependent measure, show Groups 2 and 3 not differing sig- nificantly (T(18) =.21, p = .837), with highly significant dif- ferences emerging between Group 1 and Group 3 (T(18) = —2.91, p = .009), as predicted. This is sufficient to accept the moti— 84 vated hypothesis of Experiment IV; that first language experience with a visuo-spatial gestural language has an effect on hemis- pheric processing of visuo-spatial stimuli. Post hoc analysis of individual hemispheres reveals that the two signing groups (1 and 2) are comparable in both their left hemisphere (T(18) =l.67, p= .114) and right hemisphere accuracy (T(18) = -.38, p = .708). Native signers (Group 1) and non-signers (Group 3) however, differ significantly (T(18) =2.97, p= .009) in the efficiency of left hemisphere for pro— cessing visuospatial material, with the left hemisphere of native signers reaching the highest effiociency of all groups on all stimuli (mean =.6950). 85 Experiments II and III The second phase of variance analyses was conducted on Group 1 and 2 (native signers and late acquisition signers) on all four Experimental tasks, with the essential focus on the two sign language tasks, (static and moving) of Experiments II and III. This entire analysis followed the same progression as did those just reported on words and lines, and results are shown in Table 3. Gender was again found to have no effect on overall accuracy (F(l) = .24, p = .6307); men performed no better, nor worse, than women. There was a significant interaction of Experiment X Gender (F(3) = 8.57, p = .01) indicating that men and women dif- fered in their overall accuracy when responding to separate sti- mulus types. overall accuracy (Main Effect for Groups, F(2) = 2.08, p = .1446). Experiments however did differ in overall difficulty (Main Effect for Experiment, F(l) = 7.41, p = .0112) with lowest mean scores for these two sign using groups on Expe- riment II, static signs; and the highest mean scores on Experi- ment IV, Oriented Lines (see Figure 4). There was a highly sig- nificant intereaction effect for Experiment X Hemisphere (F(l) =14.82, p = .0007) indicating that the two hemispheres performed differently across the four varying stimulus conditions. Most important a significant interaction effect between Experiment, Hemisphere and Group (F(2) =5.13, p = .013) indicates that this 86 hemisphere difference in performance to stimulus type is unique to individual groups. Figure 3 visually arrays the mean percent correct responses of the separate hemispheres for all groups on all four stimuli conditions. Insert Table 3 Insert Figure 3 87 TABLE 3 Summary of Multivariate Analyses Applied to the Experimental Data of Groups 1 and 2 on Experiments I. II, III, and IV and subanalyses of Experiments I and III df F p Multivariate Main Effect (Gender) 1 .48 '.4973 Multivariate Main Effect (Group) 1 .01 .9438 Multivariate Main Effect (Experiment) 3 3.99 .0122* Multivariate Interaction Exp X Hemi 3 6.23 .0010** Multivariate Interaction Exp X Hemi X Grp 3 3.63 .0185* Univariate G X H Interactions and Simple Effects: Experiment II (G X H) Univariate Main Effect (Grp) 1 .02 .8965 Univariate Main Effect (Hemi) l 37.50 .0000 Univariate Interaction (G X H) 1 7.13 .0156 Experiment III (G X H) Univariate Main Effect (Grp) 1 .25 .6233 Univariate Main Effect (Hemi) 6.79 .0179 Univariate Interaction (G X H) 3.02 .0995 i—‘H 88 mo I1 @011 \ DQ.IL .. 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