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Hemispheric Laterality Effects on a Facial Recognition Task in Normal Subjects
HEMISPHERIC LATERALITY EFFECTS ON A FACIAL RECOGNITION TASK IN NORMAL SUBJECTS' Ronald D. Hilliard2 (Neurosensory Center and Departments of Neurology and Psychology, University of Iowa)
Empirical investigations of facial recognition among patients with cerebral disease (cf. Hecaen and Angelergues, 1962; De Renzi and Spinnler, 1966; Warrington and James, 1967) have suggested an association between right hemisphere damage and impaired facial recognition performance. Benton and Van Allen (1968), using a matching procedure, examined facial recognition among groups of unilateral brain-damaged patients and normal control subjects. Impaired recognition of faces was observed with significantly greater frequency and greater severity among patients with right hemisphere damage than among those suffering damage to the left hemisphere. These authors concluded that the poor performance of patients with right hemisphere disease was attributable to an impairment in the integration and processing of adequately perceived sensory data. On the other hand, Milner ( 1968) concluded from her findings that right temporal lobe removal produces defect in the retention of nonverbal visual stimuli and only a mild impairment in perception. Her results further indicated that right temporal lobectomy affects memory for photographs of faces, and that this impairment is maximized when the hippocampus is included in the removal. However, De Renzi, Faglioni and Spinnler (1968) could find no evidence for the influence of a memory factor as a determinant of the differences between patients with right and left hemisphere disease on a facial identification task. Evidence for an association of impairment in facial discrimination with right hemisphere disease is one source of evidence which has led to the inference that this hemisphere assumes a distinctive role in this performance. The bulk of the research undertaken thus far involves the use of patients 1
This investigation was supported by Research Grant NS-00616 and Program-Project Grant NS-03354 from the National Institute of Neurological Diseases and Stroke. Neurosensory Center Publication No. 271. 2 This paper is based on a Ph. D. dissertation, Department of Psychology, University of Iowa.
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with brain damage due to trauma, neoplasm, vascular disease, or surgical intervention. The logical difficulty inherent in deducing localization of brain function from the incapacities manifested by an organism which has undergone even relatively well specified tissue destruction is well known. As a consequence, there has been increasing attention paid to methods which allow assessment of hemispheric laterality effects in individuals with intact nervous systems. One technique involves the tachistoscopic presentation of visual stimuli to the left or right of a central fixation point thus insuring that stimulus information is restricted to one hemisphere. This technique has been used by Rizzolatti, Umilta and Berlucchi ( 1971) to demonstrate opposite superiorities of the right and left cerebral hemispheres in discriminative reaction time to physiognomic and verbal material. Significantly shorter reaction times were found for verbal stimuli when they were presented in the right visual field, while reaction times to the faces were significantly shorter when the stimuli were presented in the left visual field. The hemispheric asymmetry demonstrated in this study was based upon differential latencies of discriminatory responses, and not upon differences in recognition accuracy, in relation to the side of the stimulus. The actual number of errors recorded for the subjects did not vary significantly with stimulus laterality, either with letters or with faces, and the authors attribute their failure to obtain a left hemisphere superiority for accuracy of letter identification to the relatively long exposure time (100 msec.). While evidence to date would suggest a more rapid overall rate of processing of physiognomic data by the right hemisphere than the left, no information is available concerning the relative level of recognition accuracy when unfamiliar faces are presented to only one of the cerebral hemispheres. Thus the first hypothesis tested in this investigation was that unfamiliar faces selectively presented to the left visual field would be accurately recognized more often than those exposed in the right visual field. A second purpose of the study was to determine whether or not laterality effects for facial stimuli would be enhanced by the introduction of a memory interval between initial and comparison presentations of the stimuli. If it is the case that the right hemisphere contains mechanism which assume a unique role in the memory for "non-verbal" visual stimuli, then the disparity between the number of correct recognitions of faces made in the right and left visual fields following an interpolated memory interval should be greater than that obtained under minimal-delay conditions. Hence, the second hypothesis tested was that the difference between recognition scores for physiognomic stimuli presented to the left and right visual fields in conjunction with a memory interval would be greater than that obtained under minimal-delay conditions. , Finally, since a right visual field superiority is rather consistently observed
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with unilateral presentations of verbal stimuli (e.g., Bryden, 1964; White, 1969a), a group of trigrams were employed in the present study both to provide a check on the effectiveness of the experimental operations and to permit within-subject comparisons of laterality differences for verbal and facial stimuli. Thus, the third hypothesis tested was that accuracy of reproduction of eve trigrams would be significantly greater following their presentation in the right visual field than in the left visual field. MATERIALS AND METHOD
Subjects
The subjects (Ss) for the experiment were 20 female University of Iowa students who ranged in age from 18 to 26 years, and who were paid for their participation. Lateral hand preferences of the Ss, as well as information concerning familial handedness patterns, were secured by administering the Neurosensory Center Handedness Questionnaire; this form was a slightly modified version of that used by Benton, Meyers and Polder ( 1962 ). All Ss rated themselves as strongly right-handed and indicated right hand preferences for at least seven of the eight reference activities listed in the questionnaire. Determination of sighting preference for each S was accomplished by observing which eye she employed when asked to view the examiner through a cone-shaped device. Right-eye sighting preferences were demonstrated by 18 of the 20 Ss; the remaining 2 Ss showed left-eye sighting dominance. Participation in the study was made contingent upon adequate performance on a battery of tests assessing various aspects of visual performance. A Bausch and Lomb Modified Ortho-Rater was used for this purpose. Included in this preliminary battery were tests of phoria, both lateral and vertical, at both far and near distances; acuity, both eyes, right eye alone and left eye alone, at both far and near distances; and stereopsis, at far distance. For each test, a range of acceptable performance was defined, and potential Ss scoring outside of these limits were excluded from the study. Apparatus
The stimuli were presented by means of a Scientific Prototype three-channel tachistoscope (Model GB), which allowed for a continuous variation of exposure times from 0.1 msec. to 110 sees. The background and exposure fields measured approximately 5 X 7 inches, subtending a horizontal visual angle of about 11" at the retina. Both types of stimulus material used in the investigation (i.e., photographs of faces and trigrams) were positioned on 5 X 7 inch white cards. A group of 24 nonsense words taken from Noble's (1961) collection of CVC trigrams comprised verbal stimuli for the reproduction task. The order of presentation of the trigrams was randomized, and conditions were arranged such that each of the 24 different trigrams in the series appeared in each visual field. The mean rated association value of the trigrams was 1.99 and the standard deviation was .01. The trigrams were printed in upper-case letters in vertical orientation 1% inches high and centered 11;4 inches either to the left or right of center of the cards. The stimuli subtended a vertical angle of approximately 2",
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and appeared about 2" either to the left or right of fixation. The order of appearance of items within the set of trigrams, as well as the visual field in which they appeared, were randomized, within the limitation that not more than three consecutive exposures occur in a single visual field. The facial stimuli employed in the study consisted of 96 achromatic photographs of draped subjects, one-half of whom were males and the other half of whom were females. All were full-face views taken under roughly uniform lighting conditions. The photographs measured approximately 11I 8 X 11I 4 inches. The facial stimuli presented during initial tachistoscopic exposure were mounted 1 :y,J inch to the left or to the right of the center of the cards; these stimuli appeared approximately 2" to the left or right fixation. The photographs presented as comparison stimuli were exposed singly in the central field. Facial stimuli varied systematically along four different dimensions: ( 1) "same" versus "different" judgement; (2) left or right visual field exposure; (3) O-see. or 10-sec. retention interval; and (4) exposure duration of 42, 54 or 66 msecs. Presentation sequence was arranged such that all possible combinations of values along the dimensions had equal privileges of occurrence.
Procedure Each of the 20 Ss in the experiment was presented the entire series of 48 trigrams and 96 faces. The sequence of tasks was constant for all Ss, the presentation of the verbal materials always preceding that of the facial stimuli. For both verbal and nonverbal recognition tasks, delivery of stimuli was unilateral and binocular viewing conditions were employed. The Ss were instructed to fixate on a central black dot prior to each stimulus presentation. Testing of the Ss was carried out individually and was completed in a single two-hour session.
Trigram reproduction Preliminary experimentation aimed at determining an optimal exposur~ duration for presentation of the trigrams revealed rather much individual variation among the six Ss tested with respect to the briefest exposures at which they were able to perceive the materials. Therefore, a procedure involving the determination of recognition limits for each individual S was adopted. During the initial threshold determination, each of eight different nonsense syllables was successively presented in each of the two visual fields. The S was asked to reproduce verbally each of the trigrams immediately following it& exposure, and her responses were recorded by the examiner. No feedback concerning the correctness of the S's responses was provided. The briefest exposure time employed during the threshold determination was 25 msecs. The exposure times were lengthened by 5 msecs. on successive blocks of four trials. That value at which the S reported perceiving three letters (regardless of their correctness) was adopted as the exposure duration for the actual experimental stimuli. The modal exposure time for the trigrams was 50 msecs. Immediately following the determination of the exposure duration, each of 24 different trigrams was successively presented, once in each of the two visual fields. Each S's score was the total number of correct reproductions for each field.
Facial recognition Six pilot Ss on whom trigram recogmt10n limits were determined were
also used to ascertain recognition thresholds for the faces. It was found that none
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of these Ss was able to recognize that the stimuli _were faces when exposed for less than 30 msecs., but that all six Ss were able to identify the stimuli as faces when exposed for 42 msecs. Results obtained with longer exposure times in this preliminary experiment indicated that exposure times of 42, 54 and 66 msecs. produced an increasing proportion of successes in identifying the individual faces by the comparison method described below. Each of the 96 trials involving facial stimuli comprised an initial and comparison exposure. S's task on each trial was to state whether or not the face appearing in the comparison presentation was the same as that which appeared in the brief initial exposure. One-half of the initial presentations were made in the left visual field, and the remaining stimuli occurred in the right visual field; comparison presentations were always in the central field of vision. Tachistoscopic exposure of target stimuli on each trial was for 42, 54 or 66 msecs., while all comparison stimuli were presented for a duration of 3 sees. The amount of time elapsing between presentations of the two stimuli on each trial was either 500 msecs. or 10 sees., hereafter referred to as the O-see. and 10-sec. memory intervals, respectively. While exposure field, memory interval values, and "same" versus "different" judgements were randomized throughout the 96 trials, the three different exposure durations were presented in blocks of 32 trials and increased systematically. The order of stimulation was the same for all Ss.
RESULTS
Facial recognition The means and standard deviations for the number of correct recognitions of faces in the left and right visual field under the O-see. and 10sec. memory interval conditions are shown in Table I. It will be noted that, by inspection, recognition performance is superior in the left visual field under both memory interval conditions. The findings were statistically evaluated by a 2 (Visual Fields) X 2 (Memory Intervals) factorial design, the data being analysed by a Treatments X Treatments X Subjects analysis of variance (ANOV A).
TABLE I
Mean and Standard Deviations for Number of Correct Recognitions of Faces in the Left and Right Visual Fields Visual field Retention interval
O-see. interval 10-sec. interval
Left
Right
Mean
S.D.
Mean
S.D.
16.95 16.30
(2.11) (2.40)
15.15 15.25
(2.14) (2.97)
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The first hypothesis tested was that a significantly greater number of faces would be correctly recognized when the stimuli were presented to the left visual field than when they were exposed in the right visual field. The hypothesis was confirmed, with the comparative accuracy of fucial recognition in the left visual field being significantly better than that in the right visual field (F = 14.32; df = 1; p < .005). The main effect of Memory Interval did not reach statistical significance (p > .05). The second hypothesis tested was that the difference between recognition scores for physiognomic stimuli presented to the left and right visual fields in conjunction with the 1O-see. memory interval would be greater than that obtained under the O-see. condition. This hypothesis was not substantiated, since the interaction of Visual Field and Memory Interval was not significant (p > .05). Trigram reproduction
The means and standard deviations for the number of correct reproductions of trigrams in the left and right visual fields are shown in Table II.
TABLE II
Means and Standard Deviations for Number of Correct Reproductions of Trigrams in the Left and Right Visual Fields
Visual field Task
eve
Right
Left
trigrams
Mean
S.D.
Mean
S.D.
9.30
(4.04)
11.25
(5.91)
A right field superiority in the perception of these verbal stimuli is sugg~sted. The data were subjected to a Treatments X Subjects ANOVA, and the results of this analysis indicate that a significantly greater number of trigrams were correctly reproduced after being presented in the right visual field than following exposure in the left visual field (F = 6.67; df = 1; p < .025). Comparison of intra-subiect laterality effects for verbal and facial materials
Of particular interest in the present investigation was the determination of the relative frequency with which individual Ss would demonstrate lateral superiority in the processing of verbal and physiognomic types of
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information. Of the 20 Ss in the experiment, 14 showed superior reproduction of trigrams presented in the right visual field, 5 Ss demonstrated superior reproduction of trigrams exposed in the left visual field, and a single S showed equally accurate reproduction for presentations in both fields. The difference between the number of Ss showing right and left visual field superiorities for the verbal materials was found to be statistically significant (p < .025) by means of the Wilcoxon Signed Ranks Test. When the facial recognition data are considered without regard to memory interval conditions (i.e., are collapsed over retention intervals), 15 of the 20 Ss showed a left visual field superiority for this task, while the other 5 Ss demonstrated superior recognition of faces presented in the right visual field. The difference between the number of Ss showing left and right visual field effects for the faces task was found to be statistically significant (p < .005) by means of the Wilcoxon Signed Ranks Test. Table III shows the relative frequencies with which various combinations of laterality effects were obtained for the two types of materials. It can be
TABLE III
Frequency of Superiority of Recognition or Reproduction in Left or Right Visual Field, for Facial and Verbal Stimuli
Superior facial recognition Right visual field
Superior trigram reproduction
Left visual field
Total
Left visual field
3
2
5
Right visual field
11
3
14
Neither visual field
1
0
1
15
5
20
Total
r.een that 11 of the 20 Ss demonstrated a left field super10t1ty for facial materials in combination with a right field superiority for verbal stimuli. Two Ss showed the opposite trend, i.e., left visual field effects for trigrams and right field effects for facial recognition. Superior recognition of both types of materials was demonstrated by three Ss when the stimuli were
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presented in the left visual field and by three Ss when the stimuli were exposed in the right visual field. Finally, one S showed a left field superiority for the perception of faces, and no field difference for the perception of trigrams. Testing of visual acuity with the Ortho-Rater device afforded information concerning acuity dominance patterns among the 20 Ss of the experiment. The findings relating these patterns and visual field effects for the two classes of stimuli are shown in Table IV.
TABLE IV
Relation of Acuity Dominance Patterns to Laterality Effects for Verbal and Facial Stimuli
Acuity dominance
Visual field effects Left
Right
Equal
Total
Verbal stimuli Left Right Equal
2 0 3
6 5 3
1 0 0
9 5 6
Total
5
14
1
20
Facial stimuli Left Right Equal
7 4 4
2 1 2
0 0 0
9 5 6
Total
15
5
0
20
DISCUSSION
The major purpose of the present investigation was to test the hypothesis· that photographs of unfamiliar faces would be recognized more accurately when presented in the left visual field than when presented in the right visual field. The hypothesis was derived from the clinical observation that prosopagnosia (i.e., the loss of ability to recognize familiar faces) is more frequently encountered in patients with disease of the right cerebral hemisphere than in patients with disease of the left hemisphere (cf. Hecaen and Angelergues, 1962) and that patients with right hemisphere disease perform more poorly on tests of facial recognition than do patients with disease of the left hemisphere (cf. Benton and Van Allen, 1968). The principal finding of the study was that accuracy of facial recognition
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performance was significantly better when the faces were presented in the left visual field than when they were presented in the right. In addition, a signicantly greater number of Ss showed superior recognition of faces in the left visual field than in the right. Thus, a hypothesis which was initially suggested by the results of neuropsychological studies carried out with braininjured subjects has been confirmed utilizing a sample of subjects with intact central nervous systems. This outcome would seem to underscore the relevance to normal brain functioning of neuropsychological research with abnormal subject populations. The finding in the present study of a left visual field superiority for the recognition of unfamiliar faces among a group of normal Ss accords well with the recent observation of a right hemisphere preference for facial identification among commissurotomy patients by Levy, Trevarthen and Sperry (1972). A second purpose of the present investigation was to evaluate the suggestion of Milner ( 1968) that difficulties in facial recognition observed in patients with right hemisphere lesions reflected a mnemonic, rather than, or in addition to, a perceptual disorder. Milner carried out a series of experiments on the visual recognition and recall performance of surgical patients who had undergone right temporal lobe excisions; her results indicated that the patients with right temporal lobe lesions were impaired in facial recognition after a short delay, with or without the introduction of an irrelevant task during the delay, but they showed no impairment under conditions of no delay. Thus, the second hypothesis tested in the present study was that laterality effects for facial stimuli would be enhanced by the introduction of a brief retention interval between initial and comparison presentations of the stimuli. This hypothesis was not confirmed, there being no demonstrably significant difference in the visual field effect for the two retention intervals. The validity of any comparisons between the data reported by Milner and those obtained by the present investigator is necessarily reduced by the sizeable methodological differences between the two studies, namely, Milner's use of a 90•sec. memory interval and simultaneous display of facial photographs, compared to the use of a 10-sec. retention interval in the present study in combination with the successive presentation of single stimuli. Nevertheless, the failure of the retention interval to show a main effect on overall accuracy in facial recognition is in accord with the findings of De Renzi, Faglioni and Spinnler (1968) and suggests that the retention of these stimuli is relatively less crucial to accuracy on this task than is their initial perception. This finding is consonant with the opinion of White ( 1969b) that, as stimulus information and exposure durations in tachistoscopic studies are reduced to a minimal level, the initial reception of the
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stimulus information becomes more crucial than its subsequent retention. In the present study, a deliberate attempt was made to maximize the degree of intra-class similarity for the facial stimuli. This was done by removing from photographed subjects any obvious cues on the basis of which recognition might be aocomplishel (e.g., eyeglasses, ears, etc.). This restriction of cues effectively reduced the amount of information conveyed by each photograph to a uniformly low level and made it necessary for the Ss in the experiment to distinguish intricate visual patterns which shared many structural attributes. That the Ss found the facial recognition task rather difficult is indicated by the finding of an average recognition accuracy of approximately 63 per cent, a figure significantly (t = 7.62, p < .005) but not strikingly above chance level. Thus, it would seem that accuracy of performance under the conditions of the present study primarily reflects perceptual rather than mnestic adequacy. A third purpose of the present investigation was to reproduce the wellestablished finding of a right field superiority for trigram recognition, in order to be confident that the present procedures were comparable to those of previous investigators and also to be able to make intra-subject comparisons of laterality effects for verbal and physiognomic stimuli. A significantly greater number of Ss demonstrated superior trigram reproduction when the stimuli were exposed in the right visual field than when they were exposed in the left; this laterality difference was shown by 70 per cent of the Ss, a proportion which corresponds closely to that found in previous investigations (cf. White, 1969a). Furthermore, a majority of Ss showed opposite lateral superiorities for the verbal and facial material, namely, a left field superiority for facial stimuli in combination with a right field superiority for the trigrams. At least two different theoretical interpretations have been advanced to account for laterality differences in visual perception. Mishkin and Forgays (1952) and Orbach (1953) reported that English words were recalled better when they were presented in the right visual field than when they were shown in the left visual field, while the recall of Hebrew words shown in the left field was superior to that of words exposed in the right. In order to account for these findings, the investigators proposed that acquired directional reading habits produce a perceptual "bias" in favor of the right visual field for English words and the left visual field for Hebrew words. This notion was subsequently elaborated by Heron (1957), who proposed a "post-exposure scanning process." This hypothetical process consists of a sequential analysis of the persisting trace of the stimulus following tachistoscopic presentation. The sequence of attending to the trace is assumed to correspond to the sequence of successive eye-fixations across the visual field with the stimulus present, if eye movements could be made. One tendency is to fixate the beginning of a sequence of letters and the other is to scan
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a sequence from left to right. Verbal stimuli exposed in the right visual field are more readily "scanned" than are those presented in the left visual field since, in the latter instance, the directional characteristics of the material and the initial scan are in discord. In the case of bilateral tachistoscopic presentation, the tendency to scan in a left-to-right direction, associated with a rapidly decaying memory trace, would result in superior recall of elements exposed in the left visual field (cf. White, 1969a). A "trace scanning" hypothesis does not satisfactorily accomodate the findings of the present investigation. This hypothesis would predict no differences between the visual fields in the recognition accuracy of stimuli which accrue no advantage from directional scanning, and so would not account for the obtained left field superiority for the recognition of unfamiliar faces. Furthermore, it is difficult to reconcile the scanning explanation with the observed right field superiority for trigram recognition, since the trigrams were vertically oriented. The formulation is clearly unable to account for the fact that a majority of Ss showed disparate within-subject laterality effects for verbal and physiognomic stimuli. An alternative theoretical formulation assigns a dominant role to the left hemisphere for language functions and to the right hemisphere ~or certain visual-perceptual and spatial functions. A major proponent of such a "cerebral dominance" explanation has been Kimura (1966) who offered the opinion that the observed right field superiority for the recognition of nonverbal stimuli is attributable to a basic functional asymmetry between the two cerebral hemispheres. If the photograph of an unfamiliar face is viewed as a rather unique and highly complex visual stimulus to which a single verbal label cannot easily be affixed, then the finding in the present study of a left visual field effect for faces is consonant with expectations drawn from a model postulating a basic functional difference between the two cerebral hemispheres. Since the explanation would also predict a right visual field superiority for verbal materials, it accounts for the findings of this study more satisfactorily than the model based upon a "trace scanning" operation. One peripheral characteristic which has been related to laterality differences in visual perception is eyedness. Ocular dominance may be defined either in terms of sighting preference (i.e., the preference of one eye over the other in sighting a distant object) or acuity dominance (i.e., the greater acuity to laterality effects under monocular viewing conditions: Overton and Wiener, 1966; Mangan, 1963). Hayashi and Bryden (1967) examined the extent to which either sighting or acuity dominance contribute to the production of laterality differences observed in tachistoscopic recognition of single letter material. These investigators found that, while ·sighting preferences were not related in any systematic manner to recognition performance, acuity dominance did bear a significant relationship to perform-
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ance under binocular viewing conditions. In the. present study, 18 of the 20 Ss exhibited a right eye sighting preference, the remaining 2 Ss showing a left eye preference. The independence of observed laterality effects and sighting preference patterns for these Ss would appear to support the contention that these two factors are unrelated. The laterality differences obtained for the classes of stimuli in this investigation were found to be relatively independent of acuity dominance patterns. Both left- and right-eye dominant Ss tended to show a left field superiority for facial recognition and a right field superiority for trigram reproduction. Thus it would seem that ocular dominance patterns exerted only a negligible effect on the obtained visual field differences. Nevertheless, it is rather interesting that of the six Ss showing equal acuity for the left and right eyes, three exhibited a left field superiority for these stimuli. These data are similar to those of Kimura ( 1966) and would suggest that laterality effects in visual perception are not significantly related to ocular dominance. The findings of the present investigation would suggest at least two possible topics for future research. The first possibility would be to examine further the role of acuity dominance characteristics in the production of laterality differences in visual perception since, in the present study, the Ss showing equally good acuity in the left and right eyes were found to show equal frequencies of left and right visual field superiorities in the reproduction of trigrams. This may have been a chance finding but deserves closer examination. In the present study, the introduction of a 10-sec. retention interval failed to exert differential effects upon facial recognition accuracy in the left and right visual fields; indeed, memory interval failed to have an appreciable effect on overall recognition accuracy. It is possible that the particular retention interval employed was too brief to provide a valid test of the contribution of mnestic factors to the production of laterality differences under these conditions. In order to assess the relative role of perceptual and memory factors in the production of laterality differences, an investigation methodologically similar to the present one, but involving a broader range of retention intervals in combination with variations in the psychological complexity (i.e., information content) of the stimuli, is indicated.
SuMMARY
Comparative recognition accuracies for physiognomic and verbal stimuli were compared when these stimuli were tachistoscopically presented to the left and right visual fields of normal dextral subjects. Results indicated that a majority of the subjects demonstrated a right visual field superiority for the recognition of trigrams, in combination with a left visual field superiority for facial recognition.
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The introduction of a 10-sec. retention interval in- the facial recognttiOn task failed to affect recognition performance appreciably, and it was concluded that the initial perception of the stimuli was relatively· more important than their subsequent retention for success on this task. The findings were interpreted within a framework of hemispheric functional asymmetry, and possible topics for future research outlined.
Acknowledgments. The author wishes to express his gratitude to Dr. H. L. Dee and Dr. A. L. Benton for their invaluable assistance throughout the course of this investigation and their helpful comments concerning the preparation of th~ manuscript.
REFERENCES BENTON, A. L., MEYERS, R., and PoLDER, G. (1962) Some aspects of handedness, "Psychiat. Neural.," 144, 321-337. - , and VAN ALLEN, M. W. (1968) Impairment in facial recognition in patients with cerebral disease, "Cortex," 4, 344-358. BRYDEN, M. P. (1964) Tachistoscopic recognition and cerebral dominance, "Percept. Motor Skills," 19, 686. DE RENZI, E., FAGLIONI, P., and SPINNLER, H. (1968) The performance of patients with brain damage on face recognition tasks, "Cortex," 4, 17-34. - , and SPINNLER, H. (1966) Facial recognition in brain-damaged patients, "Neurology," 16, 145-152. HAYASHI, T., and BRYDEN, M. P. (1967) Ocular dominance and perceptual asymmetry, "Percept. Motor Skills," 25, 605-612. HE.cAEN, H., and ANGELERGUES, R. (1962) Agnosia for faces (prosopagnosia), "Arch. Neural.," 7, 92-100. HERON, W. (1957) Perception as a function of retinal locus and attention, "Amer. J. Psycho!.," 70, 38-48. KIMURA, D. (1966) Dual functional asymmetry of the brain in visual perception, "Neuropsychologia," 4, 275-285. LEVY, J., TREVARTHEN, C., and SPERRY, R. W. (1972) Perception of bilateral chimeric figures following hemispheric deconnexion, "Brain," 95, 61-78. MANGAN, G. L. (1963) Recognition in the dominant and non-dominant visual fields, "Percept. Motor Skills," 17, 558. MILNER, B. (1968) Visual recognition and recall after right temporal-lobe excision in man, "Neuropsychologia," 6, 191-209. MISHKIN, M., and FoRGAYs, D. G. (1952) Word recognition as a function of retinal locus, "J. Exp. Psycho!.," 43, 43-48. NoBLE, C. E. (1961) Measurements of association value (a), rated associations (a'), and scaled meaningfulness ( m') for 2100 combinations of the English alphabet, "Psycho!. Rep.," 8, 487-521. ORBACH, J. (1953) Retinal locus as a factor in recognition of visually perceived words, "Amer. J. Psycho!.," 65, 555-562. OvERTON, W., and WIENER, M. (1966) Visual field position and word recognition thresholds, "J. Exp. Psycho!.," 71, 249-253. RIZZOLATTI, G., UMILTA, C., and BERLUCCHI, G. (1971) Opposite superiorities of the right and left cerebral hemispheres in discriminative reaction time to physiognomic and alphabetical material, "Brain," 94, 431-442. WARRINGTON, E. K., and JAMES, M. (1967) An experimental investigation of facial recognition in patients with unilateral cerebral lesions, "Cortex," 3, 317-326. WHITE, M. J. (1969a) Laterality differences in perception: a review, "Psycho!. Bull.," 72, 387-405. ( 1969b) Visual field differences and the recognition of alphanumeric material, "Australian J. Psycho!.," 21, 311-317.
eve
Dr. Ronald D. Hilliard, c/o Dr. A. L. Benton, Department of Neurology, University Hospitals, Iowa City, Iowa 52242, U.S.A.
Empirical investigations of facial recognition among patients with cerebral disease (cf. Hecaen and Angelergues, 1962; De Renzi and Spinnler, 1966; Warrington and James, 1967) have suggested an association between right hemisphere damage and impaired facial recognition performance. Benton and Van Allen (1968), using a matching procedure, examined facial recognition among groups of unilateral brain-damaged patients and normal control subjects. Impaired recognition of faces was observed with significantly greater frequency and greater severity among patients with right hemisphere damage than among those suffering damage to the left hemisphere. These authors concluded that the poor performance of patients with right hemisphere disease was attributable to an impairment in the integration and processing of adequately perceived sensory data. On the other hand, Milner ( 1968) concluded from her findings that right temporal lobe removal produces defect in the retention of nonverbal visual stimuli and only a mild impairment in perception. Her results further indicated that right temporal lobectomy affects memory for photographs of faces, and that this impairment is maximized when the hippocampus is included in the removal. However, De Renzi, Faglioni and Spinnler (1968) could find no evidence for the influence of a memory factor as a determinant of the differences between patients with right and left hemisphere disease on a facial identification task. Evidence for an association of impairment in facial discrimination with right hemisphere disease is one source of evidence which has led to the inference that this hemisphere assumes a distinctive role in this performance. The bulk of the research undertaken thus far involves the use of patients 1
This investigation was supported by Research Grant NS-00616 and Program-Project Grant NS-03354 from the National Institute of Neurological Diseases and Stroke. Neurosensory Center Publication No. 271. 2 This paper is based on a Ph. D. dissertation, Department of Psychology, University of Iowa.
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with brain damage due to trauma, neoplasm, vascular disease, or surgical intervention. The logical difficulty inherent in deducing localization of brain function from the incapacities manifested by an organism which has undergone even relatively well specified tissue destruction is well known. As a consequence, there has been increasing attention paid to methods which allow assessment of hemispheric laterality effects in individuals with intact nervous systems. One technique involves the tachistoscopic presentation of visual stimuli to the left or right of a central fixation point thus insuring that stimulus information is restricted to one hemisphere. This technique has been used by Rizzolatti, Umilta and Berlucchi ( 1971) to demonstrate opposite superiorities of the right and left cerebral hemispheres in discriminative reaction time to physiognomic and verbal material. Significantly shorter reaction times were found for verbal stimuli when they were presented in the right visual field, while reaction times to the faces were significantly shorter when the stimuli were presented in the left visual field. The hemispheric asymmetry demonstrated in this study was based upon differential latencies of discriminatory responses, and not upon differences in recognition accuracy, in relation to the side of the stimulus. The actual number of errors recorded for the subjects did not vary significantly with stimulus laterality, either with letters or with faces, and the authors attribute their failure to obtain a left hemisphere superiority for accuracy of letter identification to the relatively long exposure time (100 msec.). While evidence to date would suggest a more rapid overall rate of processing of physiognomic data by the right hemisphere than the left, no information is available concerning the relative level of recognition accuracy when unfamiliar faces are presented to only one of the cerebral hemispheres. Thus the first hypothesis tested in this investigation was that unfamiliar faces selectively presented to the left visual field would be accurately recognized more often than those exposed in the right visual field. A second purpose of the study was to determine whether or not laterality effects for facial stimuli would be enhanced by the introduction of a memory interval between initial and comparison presentations of the stimuli. If it is the case that the right hemisphere contains mechanism which assume a unique role in the memory for "non-verbal" visual stimuli, then the disparity between the number of correct recognitions of faces made in the right and left visual fields following an interpolated memory interval should be greater than that obtained under minimal-delay conditions. Hence, the second hypothesis tested was that the difference between recognition scores for physiognomic stimuli presented to the left and right visual fields in conjunction with a memory interval would be greater than that obtained under minimal-delay conditions. , Finally, since a right visual field superiority is rather consistently observed
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with unilateral presentations of verbal stimuli (e.g., Bryden, 1964; White, 1969a), a group of trigrams were employed in the present study both to provide a check on the effectiveness of the experimental operations and to permit within-subject comparisons of laterality differences for verbal and facial stimuli. Thus, the third hypothesis tested was that accuracy of reproduction of eve trigrams would be significantly greater following their presentation in the right visual field than in the left visual field. MATERIALS AND METHOD
Subjects
The subjects (Ss) for the experiment were 20 female University of Iowa students who ranged in age from 18 to 26 years, and who were paid for their participation. Lateral hand preferences of the Ss, as well as information concerning familial handedness patterns, were secured by administering the Neurosensory Center Handedness Questionnaire; this form was a slightly modified version of that used by Benton, Meyers and Polder ( 1962 ). All Ss rated themselves as strongly right-handed and indicated right hand preferences for at least seven of the eight reference activities listed in the questionnaire. Determination of sighting preference for each S was accomplished by observing which eye she employed when asked to view the examiner through a cone-shaped device. Right-eye sighting preferences were demonstrated by 18 of the 20 Ss; the remaining 2 Ss showed left-eye sighting dominance. Participation in the study was made contingent upon adequate performance on a battery of tests assessing various aspects of visual performance. A Bausch and Lomb Modified Ortho-Rater was used for this purpose. Included in this preliminary battery were tests of phoria, both lateral and vertical, at both far and near distances; acuity, both eyes, right eye alone and left eye alone, at both far and near distances; and stereopsis, at far distance. For each test, a range of acceptable performance was defined, and potential Ss scoring outside of these limits were excluded from the study. Apparatus
The stimuli were presented by means of a Scientific Prototype three-channel tachistoscope (Model GB), which allowed for a continuous variation of exposure times from 0.1 msec. to 110 sees. The background and exposure fields measured approximately 5 X 7 inches, subtending a horizontal visual angle of about 11" at the retina. Both types of stimulus material used in the investigation (i.e., photographs of faces and trigrams) were positioned on 5 X 7 inch white cards. A group of 24 nonsense words taken from Noble's (1961) collection of CVC trigrams comprised verbal stimuli for the reproduction task. The order of presentation of the trigrams was randomized, and conditions were arranged such that each of the 24 different trigrams in the series appeared in each visual field. The mean rated association value of the trigrams was 1.99 and the standard deviation was .01. The trigrams were printed in upper-case letters in vertical orientation 1% inches high and centered 11;4 inches either to the left or right of center of the cards. The stimuli subtended a vertical angle of approximately 2",
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249
and appeared about 2" either to the left or right of fixation. The order of appearance of items within the set of trigrams, as well as the visual field in which they appeared, were randomized, within the limitation that not more than three consecutive exposures occur in a single visual field. The facial stimuli employed in the study consisted of 96 achromatic photographs of draped subjects, one-half of whom were males and the other half of whom were females. All were full-face views taken under roughly uniform lighting conditions. The photographs measured approximately 11I 8 X 11I 4 inches. The facial stimuli presented during initial tachistoscopic exposure were mounted 1 :y,J inch to the left or to the right of the center of the cards; these stimuli appeared approximately 2" to the left or right fixation. The photographs presented as comparison stimuli were exposed singly in the central field. Facial stimuli varied systematically along four different dimensions: ( 1) "same" versus "different" judgement; (2) left or right visual field exposure; (3) O-see. or 10-sec. retention interval; and (4) exposure duration of 42, 54 or 66 msecs. Presentation sequence was arranged such that all possible combinations of values along the dimensions had equal privileges of occurrence.
Procedure Each of the 20 Ss in the experiment was presented the entire series of 48 trigrams and 96 faces. The sequence of tasks was constant for all Ss, the presentation of the verbal materials always preceding that of the facial stimuli. For both verbal and nonverbal recognition tasks, delivery of stimuli was unilateral and binocular viewing conditions were employed. The Ss were instructed to fixate on a central black dot prior to each stimulus presentation. Testing of the Ss was carried out individually and was completed in a single two-hour session.
Trigram reproduction Preliminary experimentation aimed at determining an optimal exposur~ duration for presentation of the trigrams revealed rather much individual variation among the six Ss tested with respect to the briefest exposures at which they were able to perceive the materials. Therefore, a procedure involving the determination of recognition limits for each individual S was adopted. During the initial threshold determination, each of eight different nonsense syllables was successively presented in each of the two visual fields. The S was asked to reproduce verbally each of the trigrams immediately following it& exposure, and her responses were recorded by the examiner. No feedback concerning the correctness of the S's responses was provided. The briefest exposure time employed during the threshold determination was 25 msecs. The exposure times were lengthened by 5 msecs. on successive blocks of four trials. That value at which the S reported perceiving three letters (regardless of their correctness) was adopted as the exposure duration for the actual experimental stimuli. The modal exposure time for the trigrams was 50 msecs. Immediately following the determination of the exposure duration, each of 24 different trigrams was successively presented, once in each of the two visual fields. Each S's score was the total number of correct reproductions for each field.
Facial recognition Six pilot Ss on whom trigram recogmt10n limits were determined were
also used to ascertain recognition thresholds for the faces. It was found that none
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of these Ss was able to recognize that the stimuli _were faces when exposed for less than 30 msecs., but that all six Ss were able to identify the stimuli as faces when exposed for 42 msecs. Results obtained with longer exposure times in this preliminary experiment indicated that exposure times of 42, 54 and 66 msecs. produced an increasing proportion of successes in identifying the individual faces by the comparison method described below. Each of the 96 trials involving facial stimuli comprised an initial and comparison exposure. S's task on each trial was to state whether or not the face appearing in the comparison presentation was the same as that which appeared in the brief initial exposure. One-half of the initial presentations were made in the left visual field, and the remaining stimuli occurred in the right visual field; comparison presentations were always in the central field of vision. Tachistoscopic exposure of target stimuli on each trial was for 42, 54 or 66 msecs., while all comparison stimuli were presented for a duration of 3 sees. The amount of time elapsing between presentations of the two stimuli on each trial was either 500 msecs. or 10 sees., hereafter referred to as the O-see. and 10-sec. memory intervals, respectively. While exposure field, memory interval values, and "same" versus "different" judgements were randomized throughout the 96 trials, the three different exposure durations were presented in blocks of 32 trials and increased systematically. The order of stimulation was the same for all Ss.
RESULTS
Facial recognition The means and standard deviations for the number of correct recognitions of faces in the left and right visual field under the O-see. and 10sec. memory interval conditions are shown in Table I. It will be noted that, by inspection, recognition performance is superior in the left visual field under both memory interval conditions. The findings were statistically evaluated by a 2 (Visual Fields) X 2 (Memory Intervals) factorial design, the data being analysed by a Treatments X Treatments X Subjects analysis of variance (ANOV A).
TABLE I
Mean and Standard Deviations for Number of Correct Recognitions of Faces in the Left and Right Visual Fields Visual field Retention interval
O-see. interval 10-sec. interval
Left
Right
Mean
S.D.
Mean
S.D.
16.95 16.30
(2.11) (2.40)
15.15 15.25
(2.14) (2.97)
Hemispheric laterality effects on a facial recognition task
251
The first hypothesis tested was that a significantly greater number of faces would be correctly recognized when the stimuli were presented to the left visual field than when they were exposed in the right visual field. The hypothesis was confirmed, with the comparative accuracy of fucial recognition in the left visual field being significantly better than that in the right visual field (F = 14.32; df = 1; p < .005). The main effect of Memory Interval did not reach statistical significance (p > .05). The second hypothesis tested was that the difference between recognition scores for physiognomic stimuli presented to the left and right visual fields in conjunction with the 1O-see. memory interval would be greater than that obtained under the O-see. condition. This hypothesis was not substantiated, since the interaction of Visual Field and Memory Interval was not significant (p > .05). Trigram reproduction
The means and standard deviations for the number of correct reproductions of trigrams in the left and right visual fields are shown in Table II.
TABLE II
Means and Standard Deviations for Number of Correct Reproductions of Trigrams in the Left and Right Visual Fields
Visual field Task
eve
Right
Left
trigrams
Mean
S.D.
Mean
S.D.
9.30
(4.04)
11.25
(5.91)
A right field superiority in the perception of these verbal stimuli is sugg~sted. The data were subjected to a Treatments X Subjects ANOVA, and the results of this analysis indicate that a significantly greater number of trigrams were correctly reproduced after being presented in the right visual field than following exposure in the left visual field (F = 6.67; df = 1; p < .025). Comparison of intra-subiect laterality effects for verbal and facial materials
Of particular interest in the present investigation was the determination of the relative frequency with which individual Ss would demonstrate lateral superiority in the processing of verbal and physiognomic types of
Ronald D. Hilliard
252
information. Of the 20 Ss in the experiment, 14 showed superior reproduction of trigrams presented in the right visual field, 5 Ss demonstrated superior reproduction of trigrams exposed in the left visual field, and a single S showed equally accurate reproduction for presentations in both fields. The difference between the number of Ss showing right and left visual field superiorities for the verbal materials was found to be statistically significant (p < .025) by means of the Wilcoxon Signed Ranks Test. When the facial recognition data are considered without regard to memory interval conditions (i.e., are collapsed over retention intervals), 15 of the 20 Ss showed a left visual field superiority for this task, while the other 5 Ss demonstrated superior recognition of faces presented in the right visual field. The difference between the number of Ss showing left and right visual field effects for the faces task was found to be statistically significant (p < .005) by means of the Wilcoxon Signed Ranks Test. Table III shows the relative frequencies with which various combinations of laterality effects were obtained for the two types of materials. It can be
TABLE III
Frequency of Superiority of Recognition or Reproduction in Left or Right Visual Field, for Facial and Verbal Stimuli
Superior facial recognition Right visual field
Superior trigram reproduction
Left visual field
Total
Left visual field
3
2
5
Right visual field
11
3
14
Neither visual field
1
0
1
15
5
20
Total
r.een that 11 of the 20 Ss demonstrated a left field super10t1ty for facial materials in combination with a right field superiority for verbal stimuli. Two Ss showed the opposite trend, i.e., left visual field effects for trigrams and right field effects for facial recognition. Superior recognition of both types of materials was demonstrated by three Ss when the stimuli were
253
Hemispheric laterality effects on a facial recognition task
presented in the left visual field and by three Ss when the stimuli were exposed in the right visual field. Finally, one S showed a left field superiority for the perception of faces, and no field difference for the perception of trigrams. Testing of visual acuity with the Ortho-Rater device afforded information concerning acuity dominance patterns among the 20 Ss of the experiment. The findings relating these patterns and visual field effects for the two classes of stimuli are shown in Table IV.
TABLE IV
Relation of Acuity Dominance Patterns to Laterality Effects for Verbal and Facial Stimuli
Acuity dominance
Visual field effects Left
Right
Equal
Total
Verbal stimuli Left Right Equal
2 0 3
6 5 3
1 0 0
9 5 6
Total
5
14
1
20
Facial stimuli Left Right Equal
7 4 4
2 1 2
0 0 0
9 5 6
Total
15
5
0
20
DISCUSSION
The major purpose of the present investigation was to test the hypothesis· that photographs of unfamiliar faces would be recognized more accurately when presented in the left visual field than when presented in the right visual field. The hypothesis was derived from the clinical observation that prosopagnosia (i.e., the loss of ability to recognize familiar faces) is more frequently encountered in patients with disease of the right cerebral hemisphere than in patients with disease of the left hemisphere (cf. Hecaen and Angelergues, 1962) and that patients with right hemisphere disease perform more poorly on tests of facial recognition than do patients with disease of the left hemisphere (cf. Benton and Van Allen, 1968). The principal finding of the study was that accuracy of facial recognition
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performance was significantly better when the faces were presented in the left visual field than when they were presented in the right. In addition, a signicantly greater number of Ss showed superior recognition of faces in the left visual field than in the right. Thus, a hypothesis which was initially suggested by the results of neuropsychological studies carried out with braininjured subjects has been confirmed utilizing a sample of subjects with intact central nervous systems. This outcome would seem to underscore the relevance to normal brain functioning of neuropsychological research with abnormal subject populations. The finding in the present study of a left visual field superiority for the recognition of unfamiliar faces among a group of normal Ss accords well with the recent observation of a right hemisphere preference for facial identification among commissurotomy patients by Levy, Trevarthen and Sperry (1972). A second purpose of the present investigation was to evaluate the suggestion of Milner ( 1968) that difficulties in facial recognition observed in patients with right hemisphere lesions reflected a mnemonic, rather than, or in addition to, a perceptual disorder. Milner carried out a series of experiments on the visual recognition and recall performance of surgical patients who had undergone right temporal lobe excisions; her results indicated that the patients with right temporal lobe lesions were impaired in facial recognition after a short delay, with or without the introduction of an irrelevant task during the delay, but they showed no impairment under conditions of no delay. Thus, the second hypothesis tested in the present study was that laterality effects for facial stimuli would be enhanced by the introduction of a brief retention interval between initial and comparison presentations of the stimuli. This hypothesis was not confirmed, there being no demonstrably significant difference in the visual field effect for the two retention intervals. The validity of any comparisons between the data reported by Milner and those obtained by the present investigator is necessarily reduced by the sizeable methodological differences between the two studies, namely, Milner's use of a 90•sec. memory interval and simultaneous display of facial photographs, compared to the use of a 10-sec. retention interval in the present study in combination with the successive presentation of single stimuli. Nevertheless, the failure of the retention interval to show a main effect on overall accuracy in facial recognition is in accord with the findings of De Renzi, Faglioni and Spinnler (1968) and suggests that the retention of these stimuli is relatively less crucial to accuracy on this task than is their initial perception. This finding is consonant with the opinion of White ( 1969b) that, as stimulus information and exposure durations in tachistoscopic studies are reduced to a minimal level, the initial reception of the
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255
stimulus information becomes more crucial than its subsequent retention. In the present study, a deliberate attempt was made to maximize the degree of intra-class similarity for the facial stimuli. This was done by removing from photographed subjects any obvious cues on the basis of which recognition might be aocomplishel (e.g., eyeglasses, ears, etc.). This restriction of cues effectively reduced the amount of information conveyed by each photograph to a uniformly low level and made it necessary for the Ss in the experiment to distinguish intricate visual patterns which shared many structural attributes. That the Ss found the facial recognition task rather difficult is indicated by the finding of an average recognition accuracy of approximately 63 per cent, a figure significantly (t = 7.62, p < .005) but not strikingly above chance level. Thus, it would seem that accuracy of performance under the conditions of the present study primarily reflects perceptual rather than mnestic adequacy. A third purpose of the present investigation was to reproduce the wellestablished finding of a right field superiority for trigram recognition, in order to be confident that the present procedures were comparable to those of previous investigators and also to be able to make intra-subject comparisons of laterality effects for verbal and physiognomic stimuli. A significantly greater number of Ss demonstrated superior trigram reproduction when the stimuli were exposed in the right visual field than when they were exposed in the left; this laterality difference was shown by 70 per cent of the Ss, a proportion which corresponds closely to that found in previous investigations (cf. White, 1969a). Furthermore, a majority of Ss showed opposite lateral superiorities for the verbal and facial material, namely, a left field superiority for facial stimuli in combination with a right field superiority for the trigrams. At least two different theoretical interpretations have been advanced to account for laterality differences in visual perception. Mishkin and Forgays (1952) and Orbach (1953) reported that English words were recalled better when they were presented in the right visual field than when they were shown in the left visual field, while the recall of Hebrew words shown in the left field was superior to that of words exposed in the right. In order to account for these findings, the investigators proposed that acquired directional reading habits produce a perceptual "bias" in favor of the right visual field for English words and the left visual field for Hebrew words. This notion was subsequently elaborated by Heron (1957), who proposed a "post-exposure scanning process." This hypothetical process consists of a sequential analysis of the persisting trace of the stimulus following tachistoscopic presentation. The sequence of attending to the trace is assumed to correspond to the sequence of successive eye-fixations across the visual field with the stimulus present, if eye movements could be made. One tendency is to fixate the beginning of a sequence of letters and the other is to scan
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Ronald D. Hilliard
a sequence from left to right. Verbal stimuli exposed in the right visual field are more readily "scanned" than are those presented in the left visual field since, in the latter instance, the directional characteristics of the material and the initial scan are in discord. In the case of bilateral tachistoscopic presentation, the tendency to scan in a left-to-right direction, associated with a rapidly decaying memory trace, would result in superior recall of elements exposed in the left visual field (cf. White, 1969a). A "trace scanning" hypothesis does not satisfactorily accomodate the findings of the present investigation. This hypothesis would predict no differences between the visual fields in the recognition accuracy of stimuli which accrue no advantage from directional scanning, and so would not account for the obtained left field superiority for the recognition of unfamiliar faces. Furthermore, it is difficult to reconcile the scanning explanation with the observed right field superiority for trigram recognition, since the trigrams were vertically oriented. The formulation is clearly unable to account for the fact that a majority of Ss showed disparate within-subject laterality effects for verbal and physiognomic stimuli. An alternative theoretical formulation assigns a dominant role to the left hemisphere for language functions and to the right hemisphere ~or certain visual-perceptual and spatial functions. A major proponent of such a "cerebral dominance" explanation has been Kimura (1966) who offered the opinion that the observed right field superiority for the recognition of nonverbal stimuli is attributable to a basic functional asymmetry between the two cerebral hemispheres. If the photograph of an unfamiliar face is viewed as a rather unique and highly complex visual stimulus to which a single verbal label cannot easily be affixed, then the finding in the present study of a left visual field effect for faces is consonant with expectations drawn from a model postulating a basic functional difference between the two cerebral hemispheres. Since the explanation would also predict a right visual field superiority for verbal materials, it accounts for the findings of this study more satisfactorily than the model based upon a "trace scanning" operation. One peripheral characteristic which has been related to laterality differences in visual perception is eyedness. Ocular dominance may be defined either in terms of sighting preference (i.e., the preference of one eye over the other in sighting a distant object) or acuity dominance (i.e., the greater acuity to laterality effects under monocular viewing conditions: Overton and Wiener, 1966; Mangan, 1963). Hayashi and Bryden (1967) examined the extent to which either sighting or acuity dominance contribute to the production of laterality differences observed in tachistoscopic recognition of single letter material. These investigators found that, while ·sighting preferences were not related in any systematic manner to recognition performance, acuity dominance did bear a significant relationship to perform-
Hemispheric laterality effects on a facial recognition task
257
ance under binocular viewing conditions. In the. present study, 18 of the 20 Ss exhibited a right eye sighting preference, the remaining 2 Ss showing a left eye preference. The independence of observed laterality effects and sighting preference patterns for these Ss would appear to support the contention that these two factors are unrelated. The laterality differences obtained for the classes of stimuli in this investigation were found to be relatively independent of acuity dominance patterns. Both left- and right-eye dominant Ss tended to show a left field superiority for facial recognition and a right field superiority for trigram reproduction. Thus it would seem that ocular dominance patterns exerted only a negligible effect on the obtained visual field differences. Nevertheless, it is rather interesting that of the six Ss showing equal acuity for the left and right eyes, three exhibited a left field superiority for these stimuli. These data are similar to those of Kimura ( 1966) and would suggest that laterality effects in visual perception are not significantly related to ocular dominance. The findings of the present investigation would suggest at least two possible topics for future research. The first possibility would be to examine further the role of acuity dominance characteristics in the production of laterality differences in visual perception since, in the present study, the Ss showing equally good acuity in the left and right eyes were found to show equal frequencies of left and right visual field superiorities in the reproduction of trigrams. This may have been a chance finding but deserves closer examination. In the present study, the introduction of a 10-sec. retention interval failed to exert differential effects upon facial recognition accuracy in the left and right visual fields; indeed, memory interval failed to have an appreciable effect on overall recognition accuracy. It is possible that the particular retention interval employed was too brief to provide a valid test of the contribution of mnestic factors to the production of laterality differences under these conditions. In order to assess the relative role of perceptual and memory factors in the production of laterality differences, an investigation methodologically similar to the present one, but involving a broader range of retention intervals in combination with variations in the psychological complexity (i.e., information content) of the stimuli, is indicated.
SuMMARY
Comparative recognition accuracies for physiognomic and verbal stimuli were compared when these stimuli were tachistoscopically presented to the left and right visual fields of normal dextral subjects. Results indicated that a majority of the subjects demonstrated a right visual field superiority for the recognition of trigrams, in combination with a left visual field superiority for facial recognition.
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The introduction of a 10-sec. retention interval in- the facial recognttiOn task failed to affect recognition performance appreciably, and it was concluded that the initial perception of the stimuli was relatively· more important than their subsequent retention for success on this task. The findings were interpreted within a framework of hemispheric functional asymmetry, and possible topics for future research outlined.
Acknowledgments. The author wishes to express his gratitude to Dr. H. L. Dee and Dr. A. L. Benton for their invaluable assistance throughout the course of this investigation and their helpful comments concerning the preparation of th~ manuscript.
REFERENCES BENTON, A. L., MEYERS, R., and PoLDER, G. (1962) Some aspects of handedness, "Psychiat. Neural.," 144, 321-337. - , and VAN ALLEN, M. W. (1968) Impairment in facial recognition in patients with cerebral disease, "Cortex," 4, 344-358. BRYDEN, M. P. (1964) Tachistoscopic recognition and cerebral dominance, "Percept. Motor Skills," 19, 686. DE RENZI, E., FAGLIONI, P., and SPINNLER, H. (1968) The performance of patients with brain damage on face recognition tasks, "Cortex," 4, 17-34. - , and SPINNLER, H. (1966) Facial recognition in brain-damaged patients, "Neurology," 16, 145-152. HAYASHI, T., and BRYDEN, M. P. (1967) Ocular dominance and perceptual asymmetry, "Percept. Motor Skills," 25, 605-612. HE.cAEN, H., and ANGELERGUES, R. (1962) Agnosia for faces (prosopagnosia), "Arch. Neural.," 7, 92-100. HERON, W. (1957) Perception as a function of retinal locus and attention, "Amer. J. Psycho!.," 70, 38-48. KIMURA, D. (1966) Dual functional asymmetry of the brain in visual perception, "Neuropsychologia," 4, 275-285. LEVY, J., TREVARTHEN, C., and SPERRY, R. W. (1972) Perception of bilateral chimeric figures following hemispheric deconnexion, "Brain," 95, 61-78. MANGAN, G. L. (1963) Recognition in the dominant and non-dominant visual fields, "Percept. Motor Skills," 17, 558. MILNER, B. (1968) Visual recognition and recall after right temporal-lobe excision in man, "Neuropsychologia," 6, 191-209. MISHKIN, M., and FoRGAYs, D. G. (1952) Word recognition as a function of retinal locus, "J. Exp. Psycho!.," 43, 43-48. NoBLE, C. E. (1961) Measurements of association value (a), rated associations (a'), and scaled meaningfulness ( m') for 2100 combinations of the English alphabet, "Psycho!. Rep.," 8, 487-521. ORBACH, J. (1953) Retinal locus as a factor in recognition of visually perceived words, "Amer. J. Psycho!.," 65, 555-562. OvERTON, W., and WIENER, M. (1966) Visual field position and word recognition thresholds, "J. Exp. Psycho!.," 71, 249-253. RIZZOLATTI, G., UMILTA, C., and BERLUCCHI, G. (1971) Opposite superiorities of the right and left cerebral hemispheres in discriminative reaction time to physiognomic and alphabetical material, "Brain," 94, 431-442. WARRINGTON, E. K., and JAMES, M. (1967) An experimental investigation of facial recognition in patients with unilateral cerebral lesions, "Cortex," 3, 317-326. WHITE, M. J. (1969a) Laterality differences in perception: a review, "Psycho!. Bull.," 72, 387-405. ( 1969b) Visual field differences and the recognition of alphanumeric material, "Australian J. Psycho!.," 21, 311-317.
eve
Dr. Ronald D. Hilliard, c/o Dr. A. L. Benton, Department of Neurology, University Hospitals, Iowa City, Iowa 52242, U.S.A.