Jl WWII UHIHHIUHII | HTHS A DEVELGWEE‘WM STUQY OF AS‘X'R4ME3'RY EN '5?va VESEAL HELD Thesis for the Degree of M. A. fx’iECHIGAfl STATE UNIVERSi'EY CATEERENE ELEZABE‘F H McGUiN?€ESS 1988 THE-25‘s la ‘! '47 m LIRRAR Y 141 ‘1: ‘I‘"‘-.\|“p \s‘i .t—l‘ N1;Cll.’éu,.l g) . Unzvusm _ ”.1" _-_- BINDING 8‘! nm a sour 9995 amnm mu. ‘DV .Iunrna DWI A DEVELOPMENTAL STUDY OF ASYMMETRY IN THE VISUAL FIELD by Catherine Elizabeth McGuinness Abstract of Master's Thesis Completed Fall Term. 1968 The purpose of this investigation was to study developmentally the phenomenon of perceptual asymmetry in the visual field. Previous research had indicated a su- periority in terms of recognition and stability for the right visual field of adults. It was thought that a de- velopmental study would have implications for the two major explanations which had been advanced for right field domin- ance; one in terms of cerebral dominance. the other involv- ing experience in reading the English language. The subjects of this investigation were 20 four- year-olds. 20 seven-year-olds. and 20 nine-year-olds. Each child bisected a series of horizontal and vertical lines under both binocular and monocular viewing conditions. Two pictures were drawn by each subject; one was a drawing 1 Catherine Elizabeth McGuinness of a house. a tree. and a person. the other was a free- choice drawing. Finally. each child connected two X's appearing on a sheet of paper with a horizontal straight line. Performance on these three perceptual—motor tasks was related to the variables of eye dominance. hand dom- inance. and age. Eye dominance was determined through sighting tasks and a determination of handedness was made by observing each child's performance of ten simple actions. Hand dominance and eye dominance were found to be related to the differential placement of material in the right and left picture halves under free—drawing conditions. The tendency to include more material in the right portions of pictures was related to both left-handedness and left— eyedness. A second major finding was the evidence of percep- tual asymmetry when children view a single stimulus oriented in the horizontal plane. Children have a pronounced tend- ency to displace the midpoint to the left when bisecting a horizontal stimulus line under both binocular and monocular viewing conditions. Age of the child and right-eye domin- ance were factors related to this leftward displacement tendency. Ghent's finding with adult subjects of an over 2 Catherine Elizabeth McGuinness all tendency to displace midpoints upward when bisecting vertical lines was not replicated with these children. However. the tendency to displace vertical midpoints up- ward was found to increase with develOpmental level;-aa- -empi£ieistme£~maturatienalist~explanatien~for~this~phen-— -omenon-weald—seem—teébe—supported+_. Results of this study are consistent with Gesell's finding that pre-schoolers tend to draw horizontal lines in a left—to-right direction. The highly significant re- lationship between right-handedness and left-to-right line drawing tendencies strengthens a cerebral dominance explan- ation or an explanation involving relative ease of arm movements. Further research designed to overcome several limitations of this study and to investigate other aspects of the laterality issue in a develOpmental manner was sug- gested. / ZIIZLéW/ C i "' // j ,/ 22117 . . A DEVELOPMENTAL STUDY OF ASYMMETRY IN THE VISUAL FIELD by Catherine Elizabeth McGuinness A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF ARTS Department of Psychology 1968 ACKNOWLEDGMENTS The author wishes to express her sincere apprecia— tion to Dr. John P. McKinney. adviser and chairman of the thesis committee. for his continuous guidance and encourage— ment during the planning and execution of the study and the writing of the thesis. Gratitude is also extended to Dr. Lauren Harris and Dr. Gordon Wood for their assistance and their willing- ness to serve on the committee. Special thanks are extended to the administration and students of the Holt Public Schools and to the families of Spartan Village. Michigan State University. for their willing participation in this investigation. ii TABLE OF CONTENTS Page ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . ii LIST OF TABLES. . . . . . . . . . . . . . . . . . . iv INTRODUCTION. . . . . . . . . . . . . . . . . . . . 1 METHOD. . . . . . . . . . . . . . . . . . . . . . . 13 RESULTS . . . . . . . . . . . . . . . . . . . . . . 17 DISCUSSION. . . . . . . . . . . . . . . . . . . . . 24 SUMMARY . . . . . . . . . . . . . . . . . . . . . . 32 APPENDIX. . . . . . . . . . . . . . . . . . . . . . 35 REFERENCES. . . . . . . . . . . . . . . . . . . . . 40 iii Table II. III. IV. VI. VII. VIII. IX. LIST OF TABLES PERCENTAGES OF SUBJECTS PLACING MORE MATERIAL IN LEFT THAN IN RIGHT PORTIONS OF PICTURES. . . . . . . . . . . . . . PERCENTAGES OF LEFT AND RIGHT-HANDED SS PLACING MORE MATERIAL IN RIGHT PORTION OF PICTURE . . . . MEAN DIFFERENCE SCORES FOR AMOUNT OF MATERIAL PLACED IN LEFT AND RIGHT PORTIONS OF DRAWINGS . . . . . . PERCENTAGES OF LEFT AND RIGHT-EYED SS PLACING MORE MATERIAL IN RIGHT PORTION OF PICTURE . . . . . . . . . . . . . MEAN DIFFERENCE SCORES FOR AMOUNT OF MATERIAL PLACED IN LEFT AND RIGHT PORTIONS OF PICTURE. . . . . . . . PERCENTAGES OF SS EXHIBITING VARIOUS DIRECTIONAL TENDENCIES WHEN DRAWING HORIZONTAL CONNECTING LINES. . . . PERCENTAGES OF SS DISPLACING MIDPOINTS TO THE LEFT IN HORIZONTAL LINE BISECTION TASKS. . . . . . . . . . . . . . . . PERCENTAGES OF SS DISPLACING MIDPOINTS UPWARD IN VERTICAL LINE BISECTION TASKS. MEAN AMOUNTS OF DISPLACEMENT OF MIDPOINTS WHEN BISECTING HORIZONTAL LINES. . . . MEAN AMOUNTS OF DISPLACEMENT OF MIDPOINTS WHEN BISECTING VERTICAL LINES. . . . iv Page 36 36 36 37 37 38 38 38 39 39 INTRODUCTION The present study of perceptual asymmetry in the visual field of children derives from earlier investigations with adult subjects. Mishkin and Forgays (1952) found that when letters of the alphabet were presented tachistosc0pic- ally in either the left or the right visual field. recogni— tion was better in the right. These investigators related the right—field superiority to reading experience. When English and Yiddish words were exposed tachistoscopically to readers of both languages. recognition of English words was greater to the right of the fixation point. With Yid- dish words. which are read from right to left. accuracy was superior in the left visual field. Mishkin and Forgays in- terpret their results as supporting the hypothesis that learning to read the English language involves a selective training of regions of the left hemiretinas. This leads to "a more effective neural organization" (p. 47) of the left cerebral hemisphere for alphabetic stimuli. Orbach (1952) likewise attributed the differences in recognition between the left and right visual fields to l "early visual training"; left—to-right reading habits built up over many years of practice lead to the more efficient organization of the left hemisphere. Heron (1957) suggested that an attentional process developed in the course of learning to read. in which eye movements were important. Heron found that if letters are exposed simultaneously on the right and left sides of the fixation point. more are recognized in the left field. He postulated two atten- tional processes. a "set." or tendency to concentrate on that part of the field where the stimulus is expected to appear. and a "post-exposure process." These two kinds of eye movements may be seen in reading English as a tendency to look toward the beginning of a line of print. and a tend- ency to move the eyes along it in a left-to—right manner. Heron explains the differences in recognition under simul— taneous and successive exposure conditions in terms of these two attentional processes. With presentation of stimuli at the same time in both visual fields. preferen- tial attention for the beginning of a line would cause more letters to be recognized in the left field. With presenta- tion of stimuli in either the left or right field. superior recognition would be expected in the right. with the two attentional tendencies complementing each other there. The other main type of explanation for the superior- ity of the right field with successive presentation has been in terms of cerebral dominance. Crovitz. Daston. and Zener (1959) found that subjects tended to say that an odd element in a grouping was in the visual field opposite to the preferred hand. when it had been presented in both fields with equal frequency. Bryden (1964) found no sig— nificant left-right field differences for right or left- handed subjects when the stimuli were geometric forms. When letters were presented. left-handed subjects were equally divided with regard to their dominant visual field. while the right field was dominant for most right-handed subjects. Bryden hypothesized that words are more effi- ciently analyzed in the dominant cerebral hemisphere. which contains the higher brain centers for language functions. McKinney (1966) investigated the laterality phenom— enon by means of a perceptual fragmentation technique. He had previously found (1963) that weak luminous stimuli are perceived as breaking down in an organized manner when viewed by subjects in the dark. These fragmentations are similar to the breakdowns which stabilized images undergo (Pritchard. Heron. and Hebb. 1960). Such fragmentations have been interpreted by Hebb as being indicative of break- downs in central. perceptual "cell-assemblies." McKinney was interested in whether such a central breakdown was more likely to occur in one hemisphere than in the other. His results indicated greater fragmentation in the left visual field (or greater right field stability). Thus. using the fragmentation technique. the right field was found to be superior with non-language stimuli; in the tachistoscopic studies the right field was superior only for letters (Bryden and Rainey. 1963). The difference may be due to the elimination. with the fragmentation technique. of cer— tain variables such as short-term memory and verbal label- ing which are typically involved in tachistoscopic recogni- tion studies. McKinney's finding of greater stability in the right visual field is consistent with Mishkin's hypoth— esis of a general dominance of the left visual cortex (1962). Right and left-handed subjects did not differ in amount of fragmentation in the two visual fields. McKinney (1965) also investigated the possibility of a relation between eye dominance and visual asymmetry. He found that stability was superior in the right field for right-eyed subjects. while no difference existed for left—eyed subjects. When the subjects were tested monocu- larly. the right field was found to be superior for the, left eye; no difference existed for right—eyed subjects. McKinney proposed a two-factor theory to account for these monocular results. A general dominance of the left visual cortex and a greater sensitivity in the nasal field appear to combine in the left eye to produce a right-field super— iority. while in the right eye they cancel each other out. The implications of the lateral asymmetry phenome- non in the field of art have been noted by several art his— torians. An object in a picture looks heavier in the right than in the left (Arnheim. 1954). This concurs with the general dominance of the right visual field found in the tachistoscopic studies. Wolfflin (1941) noted that when pictures are changed into their mirror images they become less meaningful to observers. He interprets this as result- ing from the fact that pictures are scanned from left to right. and the order of what is seen is reversed when pic- tures are inverted. Gaffron (1950) made a detailed study of Rembrandt's etchings and concluded that the true meaning could only be derived from the artist's original plates. not from the inverted prints. Arnheim describes Gaffron's interpretation as follows: "The observer experiences a picture as if he was facing its left side. He is subjec— tively identified with the left and whatever appears in that part of the picture assumes greatest importance" (Arnheim. 1954. p. 18). The observer creates a phenomenal. asymmetric center to the left of the true center point of the picture; the area surrounding the second center is able to carry a disproportionate amount of the weight of the picture. A related observation is that of Dean (1941) who pointed out that the members of a theater audience look to the left first as the curtain rises. The left- right phenomenon in pictures has often been given an em— piricist explanation; i.e.. it has been said to result from previous experience in reading the English language. Gaf- fron. however. relates the phenomenon to cerebral dominance. In a right-handed person. the left cortex contains the higher centers for language functions. If the left visual cortical area is also dominant. right-handed persons would be more aware of stimuli in the right visual field. Gaf- fron hypothesized that attention for the left side of a picture might be a compensation for the more articulate vision on the right side. The phenomenon of lateral asymmetry and preferen- tial attention for the left portion of the horizontal di— mension have their parallels in the vertical dimension. Ghent (1963) has found that both adults and six—year-old children attend first to the top rather than to the bottom of moderately complex figures; this is consistent with the idea that the sequential scanning of stimuli starts at the top and continues in a downward direction. at least after the pre—school years. Adults were also more likely to attend to the left than to the right of a figure. Accord— ing to Ghent. these findings with single figures suggest that more than reading habits may be involved in the find- ings of preferential recognition for parts of sequential displays. In 1920. Langfeld stated that when adult subjects attempt to bisect a vertical line. they almost always place the mark above the true midpoint. When subjects perceive lines that have been bisected accurately. the upper half will appear to be longer than the lower half. Langfeld also noted that in order for a picture to appear stable and balanced aesthetically. the heavier objects are placed near the bottom. His explanation for this perceptual illusion is in terms of "muscular strain" involved in mov— ing eyes toward the top of a picture. "This increase in effort is perceived as an increase in distance traveled or in increased size of the object" (Langfeld. 1920. p. 224). Ghent (1960) investigated Langfeld's assertion and found experimental evidence of perceptual asymmetry in the vertical axis of adults. Ghent used a series of eleven vertical lines. one of which was bisected at the midpoint. The others were divided at points ranging from 1 to 5 mm. above and below the midpoint. The subjects inspected the stimulus cards and judged whether the upper and lower halves were equal or unequal. Thirty—one out of forty subjects overestimated the size of the tOp of a vertical line. while only six subjects underestimated the upper portion. The average point of perceived equality was .575 mm. above the true midpoint. Greenough (1947) offers the obelisk and the spire as two architectural examples of the tendency to add weight to the bottom part of an object so that a sensation of ‘Visual balance may be created. Greenough suggests that tflis vertical asymmetry phenomenon has its basis in the laws of gravitation. Arnheim (1965) believes such compen- sation to keep the bottom part of an object from looking too small may result from experience with gravity. a physio- logical brain factor. or both. Nearly all the investigations of visual asymmetry have had adults as subjects. The results of a develOp— mental study of lateral asymmetry would have implications for the two major explanations which have been advanced for the phenomenon. i.e.. that it is the result of a gen- eral dominance of the left hemisphere. or that it derives from previous experience in reading English. If visual lateral asymmetry were found in pre-school. non-reading children. and if it did not appear to increase with de- velopmental level. a cerebral dominance explanation would be strengthened. 0n the other hand. the presence of de- velopmental trends in lateral asymmetry would lend support to an empiricist explanation. The present investigation was designed to study developmentally the phenomena of general right field dom— inance and corresponding preferential attention for the left visual field. Because directional differentiation Of left and right arises in the child through experimenta- ‘tion with left and right hand movements. it was decided u . O V‘ II.‘ Iv. - u- I'- a... 5.. Don. .p‘ h 0v ) 10 to investigate the visual laterality question by means of three relevant perceptual-motor tasks. Performance on Pic— ture Drawing. Line Bisection. and Line Drawing tasks was related to the variables of handedness. eyedness. and de- velopmental level. The hypothesis that right field domin- ance leads to selective attention for the left field was thus tested through the performance of certain perceptual- motor tasks by children of varying developmental levels. Knowledge of the situations in which laterality effects are evident may help in Specifying further the psycholog- ical processes underlying the differential recognition for the left and right fields. Several hypotheses were formulated on the basis of the research discussed above. 1. It seemed likely that examination of children's drawings would yield evidence of a tendency to compensate for general right-field dominance by preferential attention for the left visual field. The Picture Drawing Task was included in this experiment as a direct measure of the subjects' tendency to place more of their ma- terial in the left than in the right field. 11 Therefore. the left—minus—right score for both specified and free-choice drawings will be positive. As adults have been found to look more to the upper part of a vertical extent (Ghent. 1963) and to select bisecting points for vertical lines which are above the true midpoints (Ghent. 1966). it is hypothesized that prefer- ential attention for the left portion of a horizontal line (as a compensation for right- field dominance) will be associated with a tendency for bisection points to be displaced to the left of the true midpoints. Eye dominance and hand dominance will affect the degree of displacement of the midpoints of horizontal lines and the inclusion of more ma— terial in either the left or right portion of drawings. Ocular dominance will have different effects on displacement of the midpoints of horizontal lines under monocular as opposed to binocular viewing conditions. 12 Gesell (Yale Clinic of Child Development. 1960) found that four and five—year-old children tend to draw horizontal lines in a left—to-right manner. It is hypothesized in this investiga- tion that the proportion of subjects performing the Line Drawing task in a left—to—right manner will increase with developmental level. It would seem that such a tendency would be aug— mented by increasing practice of the left-to- right attentional process involved in reading and by writing in a left-to-right direction. While the primary concern of this study was lateral asymmetry. the related question of asymmetry in the vertical axis was also of concern. It is hypothesized that the children's performance on the vertical line bisections will confirm Ghent's finding of perceptual asymmetry in the vertical axis of adults. A tendency to displace the midpoints upward will thus be evident. METHOD Subjects. The subjects were 20 four-year—olds (X C.A. = 4.4 yrs.. range 3:9—5zl). 20 seven—year-olds 6:11—7:10). and 20 nine—year- (X C.A. = 7.5 yrs.. range olds (i C.A. = 9.4 yrs.. range = 8:11-10:3). There were 10 boys and 10 girls in each age group. The seven and nine-year-olds were second- and fourth—graders at the Sycamore Elementary School in Holt. Michigan. These children performed the Picture Drawing and Line Bisection tasks in a group setting. The experimenter later tested each child individually to determine eye dominance and hand dominance and to administer the third perceptual— motor task. The four—year-olds were children of Michigan State University students residing in married housing on the campus. These younger children performed all the experi- mental tasks in individual sessions lasting about fifteen minutes. 13 14 Experimental Procedure Determinations of Eyedness and Handedness. The criteria for eye and hand dominance used in this study were similar to those of McKinney (1965). Eye-dominance has often been determined through sighting tasks. For purposes of this study. a child was considered left- (right-) eyed if he used his left (right) eye for any three of the following four tasks: looking into a kaleid— oscope. looking through a paper cone. looking through a twelve-inch tube. and looking through a one—inch circular hole in an 8% x 11 inch paper. Likewise. to be considered right or left—handed. a child had to use one hand for at least seven of the fol- lowing ten tasks: combing hair. brushing teeth. writing. erasing a blackboard. cutting with a knife. winding a watch. opening a door. throwing a ball. cutting with scissors. and hammering a nail. Line Bisection. The subjects were given packets of white. 8% x 11 inch paper. with one horizontal or ver- tical line centered on each sheet. The children were in- structed to divide each line in half; each subject bisected 15 six lines under each of the three viewing conditions (binoc- ular. right—eyed. and left—eyed).l The stimulus lines were of three different lengths: four. five. and six inches. Order of performance of the bisections under the various viewing conditions was counterbalanced within each of the three subject groups. Picture Drawing. Each subject drew two pictures with black drawing pencils on 8% x 11 inch white paper. Half of the children in each age group were instructed first to draw a house. a tree. and a person; they were then asked to draw whatever they liked. The remainder of the subjects drew the free—choice picture first. and then the specified picture. Line Drawing. The Line Drawing task was included as a more general measure of directional tendencies. A lesser degree of motor skill is necessary for this task; thus the effect of motor skill per se on the results was lAs eleven of the four-year-olds were reluctant to wear the eye-patches which were used to create monocu— lar viewing conditions. these Ss bisected all eighteen stimulus lines binocularly. l6 expected to be minimized. Each child was instructed to connect two X's appearing about six inches apart on a sheet of 8% x 11 inch white paper. He was to draw a line from one X to the other with a black pencil. Each subject per- formed this task twice. The hand used and the horizontal direction in which the connecting line was drawn was noted. Drawing the line in the same direction both times was con- sidered as evidence of a left-to-right or right-to—left tendency. Subjects who drew the line in opposing direc- tions on the two trials were considered to show a "mixed" tendency. RESULTS Statistical Analysis. An overlay grid with one- half-inch squares was used in the analysis of the Picture Drawing results. The experimenter counted the number of squares filled in to the left and to the right of the med- ial vertical line in each picture. A left—minus-right score was determined for each child by subtracting the number of filled-in squares on the right from the corre- sponding number on the left. Mean left-minus-right scores for handedness and eyedness groups were computed. tftests being used to test for significance of differences between means. Numbers of subjects of varying eyedness and handed— ness placing more material in the right and left portions of the pictures were tabulated; the chi—square statistic was used to test for significance. The proportion of subjects in each age group exhib- iting each of three directional tendencies when performing the Line Drawing task was determined. Product-moment cor- relations were computed between directional tendencies on this task and age. eyedness. and handedness. l7 18 In analyzing the data from the Line Bisection task. the mean amount of deviation in mm. from the true midpoint was determined for each subject under each viewing-stimulus orientation condition. Thus six mean deviation scores were computed for each subject (his averages under binocular vertical. binocular horizontal. right vertical. right horizontal. left vertical. and left horizontal conditions). Mean deviation scores were computed for age levels and for viewing conditions. Percentages of subjects at each de- velopmental level displacing midpoints of vertical lines upward and midpoints of horizontal lines leftward were determined. Product—moment correlations were computed between deviation scores and eyedness. handedness. and age. Picture Drawinngask. The left-minus-right scores for the free drawings over all subjects indicate a tendency to include more material in the left portion of the picture. Fifty-eight and six—tenths percent of the children in- cluded more in the left half of their free drawings. while 41.4%.included more in the right half. (The remaining sub- jects included an equal amount of material in each half of their pictures). The pr0portions of subjects of dif— ferent ages including more material in the left than in the right portion of the pictures are given in Table I. 19 The sixty children were equally divided in their lateral preferences when drawing pictures of a house. tree. and person. 0f the total group 48.3% included more in the left. while the same proportion received negative left—minus-right scores. Under both free-choice and spec- ified drawing conditions. the seven-year—olds showed the most pronounced tendency to include more material in the left than in the right picture halves. Handedness was related to asymmetrical placement of material in the free drawings. As Table II indicates. on the free-drawing task 71.1% of the left—handed subjects put more of their drawing in the right. while only 35.5% of the right-handed subjects put more in the right. The relationship between left-handedness and the tendency to include more material in the right field approached statis- tical significance (X2 = 3.67. d.f. = l. .05 < p < .10). Handedness was not significantly related to asymmetrical placement of material in the HTP pictures. Just as the tendency to include more in the right field is associated with left—handedness. so it is related to left-eye dominance. Greater proportions of left-eyed subjects than right-eyed subjects included more of their 20 drawing in the right field (Table IV). While the chi- square analysis indicated that this relation was not sig- nificant for the HTP pictures. eye-dominance was signifi- cantly related to asymmetrical placement of material in the free drawings (X2 = 4.84. d.f. = l. p < .05). Similar associations between both eyedness and handedness and left and right field placement were evident when amount of material was considered. although the re- sults of the E-tests were not statistically significant (Tables III and V). Line Drawing Task. The directional tendencies in horizontal line drawing for children of different ages are presented in Table VI. The tendency to connect the X's in a left-to-right manner predominated at each developmental level. For the four-year-olds and nine—year—olds. the proportion of subjects exhibiting the left-to-right tend- ency was significantly greater than the proportion connect— ing the stimuli in a right-to-left manner. The left-to- right tendency on this task was not found to increase with developmental level. An association with handedness is apparent. Right- ihanded children were significantly more likely to draw 21 horizontal connecting lines in a left-to-right manner than were left-handed children (X2 = 11.71. d.f. = l. p < .001). Seventy-seven and four-tenths percent of the right-handed subjects. but only 14.3 percent of the left-handed subjects performed the Line Drawing task in a left-to—right manner. Line Bisection Task. Percentages of subjects of varying ages displacing the midpoints of horizontal lines to the left when bisections were done under the various viewing conditions are given in Table VII. In eight of the nine age-viewing condition categories. greater propor- tions of subjects selected a bisection point which was dis— placed to the left as Opposed to the right of the true mid— point; in only one category did proportionately more sub- jects choose a bisection point which was displaced right— ward. The mean amounts of displacement of the bisection points to the left of the true midpoints for the varying develOpmental levels and viewing conditions are presented in Table IX. Over all 60 subjects. the average bisection point selected under binocular conditions was 1.07 mm. to the left of the true midpoint. When sighting was left- eyed. the average point of perceived equality was 1.12 mm. 22 to the left of the true midpoint. The greatest amount of displacement resulted under right—eyed viewing conditions. where the mean amount of movement to the left was 1.43mm. The data indicate that as age increases so does the tendency to displace the midpoints of horizontal lines to the left. under binocular viewing conditions. The product-moment correlation coefficient between age of subject and number of millimeters the perceptual midpoint was displaced to the left of the real midpoint was .381. which is highly significant (p = .002. two—tailed). Right-eyedness was also found to be related to leftward displacement tendencies. The product-moment cor- relation between right-eye dominance and amount of dis- placement of the midpoint leftward was highly significant under right-eyed viewing conditions (r = +.407. p = .003. two-tailed). The results for left-eyed and binocular viewing conditions were consistent in terms of direction. although not statistically significant (5 = +.208. p = .142 and_£ = +.184. p = .151. respectively). Percentages of Ss for whom the perceptual midpoint of vertical lines was above the true midpoint are indicated in Table VIII. A greater proportion of the seven- and nine— year-old children displaced the midpoints upward than 23 downward; only among the four-year—olds did downward dis— placement tendencies predominate. Mean amounts of displacement of the bisection points from the true midpoints of the vertical line stim- uli can be seen in Table X. Over-all mean scores are nega- tive for all three viewing conditions. indicating that the average bisection points for the sixty 85 were below the true midpoints. The greatest degree of downward displace- ment resulted when the stimulus lines were viewed with the right eye. Developmental level was found to correlate signifi- cantly with tendency to displace the midpoints upward when bisecting vertical lines under right- and left-eyed view— ing conditions. (The product—moment correlations and cor— responding probabilities were r = +.403. p .0034; and r = .268. p = .057. respectively). Left handedness correlated +.30 (p .032) with upward displacement tendencies under right-eyed viewing conditions and correlated +.263 (p = .061) when the chil— dren viewed the stimuli with their left eyes. DISCUSSION Several conclusions seem apparent from the above data. First. hand dominance and eye dominance are related to the tendency of children to include more material in the left than in the right portion of pictures when they are allowed to draw anything they choose. No significant over-all tendency toward inclusion of more material in the left picture half as a compensation for general right' field dominance was evident. However. right-handed chil— dren (for whom the left cerebral hemisphere. and thus the right visual field. would be dominant) included more of their drawing in the left visual field. while left-handed children (with dominance of the right cerebral hemisphere and the left viSual field) put more material in the right field. Thus children seem to compensate for the physio- logically determined dominance of one visual field by plac- ing more material in the opposite portion of the paper when they are drawing free-choice pictures. An alterna- tive explanation in terms of ease of expressive movements is possible. It is easier and more natural for a person 24 25 using his right hand to make the movements involved in drawing in the area of the paper that is further away from the hand and arm being used. Eye dominance exerted an influence in the same direction; right-eyed children placed more material in the left portion of their free drawings. while left-eyed children put more material in the right halves of the pic— tures. This is consistent with McKinney's (1965) finding that the superiority of the right field is related to right-eye dominance. When the children were instructed what to draw. neither eyedness nor handedness was significantly related to asymmetrical drawing tendencies. although the results were similar in direction to the data from the free—choice drawings. When drawing under a given set. the children may have been more aware of the need to create a balanced picture. and therefore exerted more control over the ten- dencies toward asymetrical drawing evident under the free- choice drawing condition. A second major finding of this investigation is the evidence of perceptual asymmetry when children View a single stimulus oriented in the horizontal plane. Children 26 have a pronounced tendency to displace the midpoint to the left when bisecting a horizontal stimulus line. The aver- age point of perceived equality was 1.07 mm. to the left of the point of physically equal magnitude. when the bisections were done under binocular viewing conditions. Leftward dis- placement tendencies were even more pronounced under monoc- ular viewing conditions. These results are consistent with the prediction that preferential attention for the left portion of a horizontal extent would result in a tendency for bisection points to be displaced to the left. This represents support for Mishkin's (1962) hypothesis of a general dominance in the visual area of the left cerebral cortex; right field dominance results. which in turn leads to selective preferential attention for the left field. Developmental factors are also relevant; the rela- tion between age of the child and degree of displacement of the horizontal midpoints to the left was highly signif— icant. This evidence of a developmental trend in lateral asymmetry can be interpreted as supporting an empiricist View; the tendency to create a subjective. perceptive cen- ter to the left of the true physical center of a horizontal line may be strengthened by the left-to-right eye movements practiced in reading the English language. A maturational- ist explanation might also be proposed. 27 Right-eye dominance was a second factor found to be related to leftward displacement tendencies for hori- zontal line midpoints. This is consistent with McKinney's finding that the superiority of the right visual field is greater for right-eyed than for left—eyed subjects. Al- though right—eyed children tended to displace the midpoints to the left under binocular and left—eyed viewing condi- tions. right-eye dominance exerted a differential effect on leftward displacement tendencies when the viewing was done with the dominant eye. Although proportionately more children moved the midpoints of the vertical stimulus lines upward than down- ward. mean amounts of displacement were in a negative (downward) direction. Thus no over-all tendency to dis- place vertical line midpoints upward was evident. as Ghent (1960) had found with an adult sample. However. the tend- ency to displace vertical midpoints in an upward direction was found to increase with developmental level; an empiri- cist explanation would seem to be supported. The bottom parts of objects may come to look heavier due to experience with gravitational forces; the fact that attentional pro— cesses are directed to the top of vertical figures. as 28 Ghent found. would seem to be compensation for the domin- ance and heaviness of the lower portions. of which one be- comes more conscious with increasing experience in living in the world. The difference in our awareness of the top and bottom portion of a vertical extent seems comparable to the difference in awareness of the left and right por— tion of a horizontal stimulus; similar processes may ac- count for these instances of asymmetry. For both dimen- sions. the evidence indicates that the perceptual midpoints are displaced from the true centers in the opposite direce tion from the area of greatest visual dominance. The heaviness of bottom and right appear to cause subjective identification with top and left and. further. result in the selection of midpoints for these line stimuli which are displaced toward the top and left. respectively. A compensatory mechanism to make up for perceptual asymmetry in the visual field seems to be operating when children divide lines in half. Results of the present study are consistent with Gesell's finding (1960) that four and five-year-olds tend to draw horizontal lines in a left-to—right manner. As the left—to-right drawing tendency is as prevalent in 29 pre-schoolers as in children who have been reading for approximately four years, an empiricist explanation for left-to-right drawing tendencies is not supported. It does not seem likely that this tendency results from the left-to—right eye movements involved in reading English. Rather. the highly significant relation between right- handedness and left-to-right drawing tendency strengthens a cerebral dominance explanation. Preferential attention for the stimulus in the left field (because of right field dominance) may cause the right-handed child to begin at the left when he connects two stimuli with a horizontal line. The reverse is true of left-handed children. Rela- tive ease of arm and hand movement may also be a factor. It would seem intrinsically easier for a right-handed per- son to begin a horizontal line drawing in the section of the paper furthest away from the arm being used and to con- tinue in a rightward direction than to proceed in the Oppo- site manner. Two limitations in this investigation should be kept in mind. As left-handedness is much less prevalent in the pOpulation than is right-handedness. and since the children were selected randomly at each age-level. only 3O seven of the total group of sixty children proved to be left-hand dominant. The restricted sample of left-handed behavior which resulted lessens the degree of confidence which should be placed in the conclusions. An extension of this study with the inclusion of a greater number of left—handed subjects might be profitable in clarifying further the relation between cerebral dominance and per- formance on these several perceptual-motor tasks. Secondly. while all of the children seemed to com- prehend and respond positively to the picture drawing and line-drawing tasks. some of the youngest children may not have completely understood what they were being asked to do with regard to line bisections. Research on visual lateral asymmetry has been mainly done with adults as subjects. As develOpmental research has important implications for the visual asym- metry issue. further investigations with children of situa- tions in which laterality effects are evident would seem to be desirable. The generality of the relationships found in this investigation between eyedness. handedness. and age might be explored by studying children's perform- ances on other perceptual-motor tasks. A fragmentation 31 study to see whether the relatively greater stability of the right visual field is developmental would also be a possibility. SUMMARY The purpose of this investigation was to study developmentally the phenomenon of perceptual asymmetry in the visual field. Previous research had indicated a super- iority in terms of recognition and stability for the right visual field of adults. It was thought that a develop- mental study would have implications for the two major explanations which had been advanced for right field dom—' inance; one in terms of cerebral dominance. the other in— volving experience in reading the English language. The subjects of this investigation were 20 four— year-olds. 20 seven-year-olds. and 20 nine-year-olds. Each child bisected a series of horizontal and vertical lines under both binocular and monocular viewing conditions. Two pictures were drawn by each subject; one was a drawing of a house. a tree. and a person. the other was a free- choice drawing. Finally. each child connected two X's appearing on a sheet of paper with a horizontal straight line. Performance on these three perceptual—motor tasks was related to the variables of eye dominance. hand 32 33 dominance. and age. Eye dominance was determined through sighting tasks and a determination of handedness was made by observing each child's performance of ten simple actions. Hand dominance and eye dominance were found to be related to the differential placement of material in the right and left picture halves under free—drawing conditions. The tendency to include more material in the right portions of pictures was related to both left—handedness and left— eyedness. A second major finding was the evidence of percep- tual asymmetry when children view a single stimulus oriented in the horizontal plane. Children have a pronounced tend- ency to displace the midpoint to the left when bisecting a horizontal stimulus line under both binocular and monoc- ular viewing conditions. Age of the child and right—eye dominance were factors related to this leftward displace- ment tendency. Ghent's finding with adult subjects of an over-all tendency to displace midpoints upward when bisect- ing vertical lines was not replicated with these children. However. the tendency to displace vertical midpoints upward was found to increase with developmental level; an empiri- cist or maturationalist explanation for this phenomenon would seem to be supported. 34 Results of this study are consistent with Gesell's finding that pre-schoolers tend to draw horizontal lines in a left—to-right direction. The highly significant rela- tionship between right-handedness and left-to—right line drawing tendencies strengthens a cerebral dominance explan- ation or an explanation involving relative ease of arm movements. Further research designed to overcome several limitations of this study and to investigate other aSpects of the laterality issue in a developmental manner was sugé gested. APPENDIX 36 TABLE I PERCENTAGES OF SUBJECTS PLACING MORE MATERIAL IN LEFT THAN IN RIGHT PORTIONS OF PICTURES (N = 60) Age Free Choice House. Tree. Person 4 55% 40% 7 70% 60% 10 50% 45% TABLE II PERCENTAGES OF LEFT AND RIGHT-HANDED SS PLACING MORE MATERIAL IN RIGHT PORTION OF PICTURE Handedness Free HTP Left-handed 71.4% 57.1% Right-handed 35.3% 47.2% TABLE III MEAN DIFFERENCE SCORES FOR AMOUNT OF MATERIAL PLACED IN LEFT AND RIGHT PORTIONS OF DRAWINGS Handedness Free HTP Left-handed —l4.6 —6.52 Right—handed +6.29 +2.87 (Positive score indicates greater amount placed in left field.) 37 TABLE IV PERCENTAGES OF LEFT AND RIGHT-EYED SS PLACING MORE MATERIAL IN RIGHT PORTION OF PICTURE Eyedness Free HTP Left-eyed 57.1% 61.9% Right-eyed 28.2% 39.5% TABLE V MEAN DIFFERENCE SCORES FOR AMOUNT OF MATERIAL PLACED IN LEFT AND RIGHT PORTIONS OF PICTURE Eyedness Free HTP Left-eyed -4.66 -4.24 Right—eyed +3.72 +5.00 (Positive score indicates greater amount placed in left field.) TABLE VI PERCENTAGES OF SS EXHIBITING VARIOUS DIRECTIONAL TENDENCIES WHEN DRAWING HORIZONTAL CONNECTING LINES (N = 60) Age Left-to-Right Right-to—Left Mixed 4 75% 20% 5% 7 60% 30%. 10% 9 75% 10% 15% 38 TABLE VII PERCENTAGES OF SS DISPLACING MIDPOINTS TO THE LEFT IN HORIZONTAL LINE BISECTION TASKS (N = 60) Age Left~eyed VieWing Binocular Right—eyed Viewing 4 78% 35%* 55% 7 80% 75% 90% 9 65% 60% 65% TABLE VIII PERCENTAGES OF SS DISPLACING MIDPOINTS UPWARD IN VERTICAL LINE BISECTION TASKS Age Left-eyed Viewing Binocular Right—eyed Viewing 4 33%* 53% 22%* 7 65% 55%. 50% 9 75% 70% 65% * indicates categories where proportion of Ss displacing midpoint to the left or upward is inconsistent with the hypothesis. ' 39 TABLE IX MEAN AMOUNTS OF DISPLACEMENT OF MIDPOINTS WHEN BISECTING HORIZONTAL LINES (N = 60) Binocular . Age Horizontal Left-eyed Right—eyed Mean 4 -1.24 mm - .64 mm -1.05 mm '2 = -.97 mm 7 +3.3 +2.82 +4.24 'E = 3.45 9 +1.1 +1.19 +1.09 'i = 1.13 'E = 1.07 mm 'E = 1.12 mm 'M = 1.43 mm TABLE x MEAN AMOUNTS OF DISPLACEMENT OF MIDPOINTS WHEN BISECTING VERTICAL LINES (N = 60) Age Binocular Left—eyed Right-eyed Mean 4 + .14 mm -2.0 mm -5.83 mm 'M = -2.56 mm 7 -1.39 - .2 - .76 'E = — .72 9 +1.23 +2.16 - .88 'E = + .83 'i = -.2mm 'E = -.013 mm 'i = -2.49 mm REFERENCES Arnheim. Rudolf. Art and visual perception. Berkeley and Los Angeles: University of California Press. 1965. Bryden. M. P. Tachistoscopic recognition and verbal domin- ance. Percept. mot. Skills. 1964. 12. 686. Bryden. M. P.. and Rainey. C. A. Left—right differences in tachistoscopic recognition. J. exp. Psychol.. 1963. 66. 568-571. Crovitz. H. F.. Daston. P. G.. and Zener. K. E. Laterality and the phenomenon of localization. Percept. mot. Skills: 1959: 2} 282. Dean. Alexander. Fundamentals of play directing. New York: Holt. 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