Lateral Preferences and Performance on Non-Verbal Laterality Tests in a Normal Population

LATERAL PREFERENCES AND PERFORMANCE ON NON-VERBAL LATERALITY TESTS IN A NORMAL POPULATION Esther Strauss and Susan M. Goldsmith (Department of Psychology, University of Victoria, British Columbia, Canada)

For the past century, intense interest has focussed on the relations between lateral preferences and cerebral language dominance. The evidence from studies of clinical and normal populations suggests that hand preference provides relevant, but not very accurate, information regarding language lateralization (e.g. Hardyck and Petrinovitch, 1977; Rasmussen and Milner, 1977; Satz, 1980; Strauss and Wada, 1983). It is estimated that more than 95 percent of right-handers have speech located in the left hemisphere while in left-handers the incidence of left hemisphere speech dominance is only 60 to 70 percent. The relation between language dominance and foot preference is similar to that observed for handedness (Strauss and Wada, 1983). Right-footed people are more likely than left-footed people to show left hemisphere language dominance. There is also evidence (Searleman, 1980; Strauss, 1986) that footedness may be a better indicator of language lateralization than handedness in normal people because it is less susceptible to cultural bias. The literature on sense organs is less conclusive. There seems to be little relation between eyedness and cerebral language representation (Bryden, 1982; Porac and Coren, 1981; Searleman, 1980; Strauss, 1986; Strauss and Wada, 1983; White, 1969; but see Levy and Gur, 1980). On the other hand, ear preference appears to show some association to indicators of language lateralization at least in normal people (Porac and Coren, 1981; Strauss, 1986; but see Strauss and Wada, 1983). Individuals who prefer to listen with their right ear are more likely than their left-sided counterparts to show a right ear advantage (REA) on verbal dichotic listening tests. This effect, however, may be specific to certain types of verbal dichotic listening tasks (Williams, 1982). Finally, there is some additional evidence that the degree of congruency across indexes (all Cortex (1987) 23, 495-503

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right, all left, mixed) has predictive value in assessing language lateralization (Searleman, 1980; Strauss, 1986; Strauss and Wada, 1983). Left hemisphere language representation is more likely to occur with congruent right-sidedness whereas right hemisphere language dominance is more typical of congruent left-sidedness. Thus, the weight of evidence to date suggests that in normal people, footedness and overall congruency are the best predictors of language lateralization. Although it is generally assumed that the right hemisphere is specialized for non-verbal abilities in much the same way as the left hemisphere is specialized for language, there has been relatively little investigation of the relation of lateral preferences to the functions of the non-speech dominant hemisphere (Bryden, 1982). Some information is available on the relation between handedness and lateralization of non-verbal functions. With regard to clinical data, some (Hecaen, De Agostini and MonzonMontes, 1981) have found that the dependence of visuo-spatial functions on the right hemisphere is less extreme in left-handers than in righthanders. Others (Masure and Benton, 1983; Tzavaras, Hecaen and LeBras, 1971) however, have reported that hemispheric organization with respect to the mediation of visuospatial performance does not differ in right- and left-handers. In the literature concerning normal people, lefthanders often show identical asymmetries in performance to right-handers but can also show no asymmetries or trends in the direction opposite to right-handers (see Annett, 1982; Ley and Strauss, 1986; for recent reviews). Thus, as is the case with language specialization, there seems to be only a weak relation between handedness and non-verbal lateralization. Turning to eyedness, Bryden (1973) found no relation between sighting dominance and performance on a non-verbal laterality task. However, the perceptual task also failed to show any significant visual field effect. Thus, it remains possible that eyedness is related to aspects of hemispheric specialization. We are unaware of any studies that have assessed the associations between non-verballateralization and the other subject variables of footedness, earedness and overall congruency. The purpose of the present study was to examine in normal people the ability of five main subject variables (handedness, footedness, eyedness, earedness and overall congruency) to predict laterality on non-verbal tasks. If the right hemispere is specialized for non-verbal abilities in much the same way as the left hemisphere is specialized for language, then we might expect that the subject variables that are most predictive of language laterality, namely footedness and overall congruency, would also be the best predictors of nonverbal lateralization.

Non verba/laterality ExPERIMENT

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I

Materials and Method Subjects

Of the 51 undergraduate students who volunteered as subjects, 33 were women (mean age = 23.6). Only subjects who reported no visual or neurological deficits were tested. Procedure (1) Visual Half-field Task

Eighteen black and white photographs of three male and three female caucasian models, trained to display anger, fear and disgust were selected from a set by Ekman and Friesen (1975). There were eighteen stimulus pairs in which the face and the expression were identical (same face/ same expression). Each ofthese pairs was duplicated, yielding 36 same face/same expression pairs. For 36 stimuli, the pair members were of the same people displaying different expressions (same face/different expression). Two slides were made of each of the 36 same expression and 36 different expression pairs, resulting in 144 pairs of slides. For each pair, the first member appeared in the center of the first slide and the second member appeared in the right half of the second slide. The duplicate pair was identical except that the second slide was reversed when it was placed in the slide tray. This resulted in the second face appearing in the left half of the second slide. In this way, when projected, the first member of a pair appeared at the fixation point and the second member appeared to either the right or left of the fixation point. The experiment consisted of 4 blocks of 36 trials, for a total of 144 trials. In each block, there was a random ordering of 9 same expression and 9 different expression pairs, occurring in each visual field. The two factors, visual field (left, right) and expression type (same, different), never occurred more than three times in succession. The first face of a pair appeared at a central fixation point. The second member of a pair began 1.5 cm to the right or left of the fixation point. Each face covered a 3.4 by 4.8 cm area on the screen. Since the subject sat approximately 60 cm from the screen, the center of the image fell about 2.97 degrees from the fovea. Subjects were instructed to sort the eighteen photographs of the emotional faces into the three affective categories: anger, fear or disgust. Subjects were then seated before a translucent screen and were instructed to place their index finger on a centrally positioned response key. They were then told that a face would appear at a central fixation point followed by another face to either the right of left of fixation and that the second member of the pair would always be of the same individual. Subjects were instructed to depress the response key as quickly as possible whenever the expression of the second member of the pair was different from that of the first member. They were instructed not to respond when the pair members displayed the same expression. The first slide of the pair was presented centrally for 1000 msec. The second member of the pair was presented to either the right or left visual field for 200

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msec. The interval between target and test item was 50 msec. Two Kodak carousel projectors, with electromechanical shutters (Eastman Kodak Co., model B-20), were used to back project the target and test faces on the translucent screen. A timer (SWTPC) started as soon as the second member of the pair was projected onto the screen. The subject's response stopped the timer and his latency from onset of the test stimulus was recorded to the nearest msec. A trial occurred every 5 seconds. At the beginning of each block, the subject was reminded to fixate at the center of the screen. The test session lasted approximately 25 minutes. At the beginning of the test session, subjects were provided with 10 practice trials with feedback regarding accuracy given on each trial. Scores were derived for each subject using the formula (L- R) where L represents the response latency to stimuli presented to the LVF and R, the response time to stimuli presented to the RVF. Thus, negative scores reflect a LVF superiority while positive scores represent a RVF advantage. (2) Questionnaire

Subjects were asked to complete a behaviorally validated self-report inventory used to assess hand, foot, eye and ear preference (Porac and Coren, 1981). This inventory contained 16 items, 4 for each index. The handedness items were: (1) With which hand do you use an eraser? (2) With which hand do you remove the top card when dealing? (3) With which hand would you throw a ball to hit a target? (4) With which hand do you draw? The footedness items were: (1) With which foot would you kick a ball? (2) If you had to step onto a chair, which foot would you place on the chair first? (3) If you wanted to pick up a pebble with your toes, which foot would you use? (4) Which foot would you use to step on a bug? The eyedness items were: (1) With which eye would you peep through a keyhole? (2) If you had to look into a dark bottle to see how full it was, which eye would you use? (3) Which eye would you use to sight down a rifle? (4) Which eye would you use to sight down a telescope? The earedness items were: (1) Into which ear would you place the earphone of a transister radio? (2) If you wanted to listen in on a. conversation going on behind a closed door, which ear would you place against the door? (3) If you wanted to hear someone's heart beat, which ear would you place against their chest? (4) Imagine a small box resting on a table. The box contains a clock. Which ear would you press against the box to find out if the clock was ticking? The items have been validated against performance measures in normal people, yielding an average question-performance concordance rate of 90 percent (Porac and Coren, 1981). Subject responded to each question with an answer of left, right or both. Scores were derived for each index using the formula (R minus L)/N where R represents the number of 'right' responses, L the number of 'left' responses and N the total number of items used to measures any given type of lateral preference (Porac and Coren, 1981). Scores for each index range from - 1 to + 1, where negative values represent a predominance of left response and positive values reflect a predominance of right responses. RESULTS

In the sample as a whole, all indexes showed a predominance of right-sidedness. Handedness showed the largest dextral bias (86.3%),

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TABLE I

Relation between Visual Half-Field (VHF) Index and Lateral Preference

VHF

p

Hand p Foot

p

~

Hand -.18 .20

Foot -.10 .48 .75 .00

Eye -.38 .006 .61 .00 .53

m

p

Ear -.21 .14 .31 .02 .47

m

M

.004

Ear

p

Overall * -.23 .l0 .40 .004 .55 ~

~

.00 .68 .00

Note. (Coefficient! 2-tailed sig). *In this analysis, for overall congruency, subjects were classed as being totally right-sided or not.

followed byfootedness (72.5%), eyedness (66.7%) andearedness (62.75%). With regard to overall congruency, many subjects (45.1 %) were biased in favour of the right side on all four lateral preference indexes while few (9.8%) showed a consistent left-sided preference pattern. The remainder (4.5.1 %) lacked consistent sidedness. On this visual half-field task, 66.7% of the sample showed a LVF superiority and 33.3% had a RVF advantage. In none of our analyses did the behavior of males and females differ. Consequently, the data for these two groups were pooled. A multiple regression analysis based upon the individual measures (hand, foot, eye, ear, overall congruency) revealed that a small, but significant amount of the variance (r square = .15) in visual laterality scores could be explained by eyedness (F = 8.39; dJ. = 1, 49; p = .006). As shown in Table I, no other variable added a significant contribution. Errors were few, occurring on 6.2% of the LVF and 6.4% of the RVF trials. None of the effects involving errors reached significance. EXPERIMENT 2

Materials and Method Subjects

As part of another larger study on brain structure-function relations, a group of adults with no auditory or neurological deficits were given a non-verbal dichotic listening test and a lateral preference questionnaire. Forty-eight new subjects, 23 males (mean age = 33.6) and 25 females (mean age 26.8), volunteered in the study. About half preferred the right motor and sense organs and half preferred the left-sided motor and sense organs.

Esther Strauss and Susan M. Goldsmith

500

Procedure (1) Dichotic Listening Test

The stimuli (Saxby and Bryden, 1984) consisted of four different verbal phrases spoken in four different tones-of-voice: happy, sad, angry and neutral. Each of the 96 trials consisted of a dichotic presentation of two different stimulus sentences immediately followed by a binaural presentation of a third stimulus sentence. For each trial, the affective tone in which the sentences were spoken varied and the verbal content remained constant. On half the trials, subjects were told to attend to the right ear only. On the other half of the trials, they were told to listen to the left ear only. For each trial, subjects were instructed to state whether the tone-of -voice they heard in the attended ear on the dichotic and binaural presentation was the same or different. On half the trials, the correct response was 'same', on the other half the correct response was 'different'. Eight practice trials, with feedback regarding accuracy given on each trial, were provided at the start of the test. The tape was played on a Sony stereo tape recorder through matched headsets. Sound amplitudes were equated (about 80 dB SPL) at each of the speakers of the set of stereo headphones by means of a sound meter. The earphones were reversed for each subject for half of the trials. Scores were derived for each subject using the formula (R minus L)/ (R plus L) where R represented the number of correct responses to right ear trials and L the number of correct responses to left ear trials. Thus, negative scores reflect a LEA while positive scores represent a REA. (2) Questionnaire

Subjects completed the lateral preference questionnaire described in Experiment 1.

TABLE II

Relation between Ear Asymmetry (EA) Index and Lateral Preference

EA P Hand p Foot p Eye p Ear p

Hand

Foot

Eye

Ear

Overall*

-.17

-.19 .20 .94 .00

-.33 .02 .88 .00 .88 .00

-.23 .12 .84 .00 .87 .00 .76 .00

-.27 .06 .79 .00 .82 .00 .76 .00 .93 .00

.25

Note. (Coefficient / 2-tailed sig). * In this analysis, for overall congruency, subjects were classed as being totally right-sided or not.

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RESULTS

On this dichotic listening task, 73% of the sample showed a LEA while only 27% showed a REA. A multiple regression analysis based upon the individual measures (hand, foot, eye, ear, overall congruency) revealed that a small but significant amount of the variance (r square = .11) in auditory laterality scores could be explained by eyedness (F = 5.64; dJ. = 1,46; P = .02). As shown in Table II, none of the other variables added a significant contribution. DISCUSSION

The goal of the present study was to determine if, in a normal population, handedness, footedness, eyedness, earedness and congruency across lateral preferences were predictive of perceptual asymmetry on non-verbal laterality tasks. We did not observe an association between hand preference and perceptual advantage. Although a trend was apparent in our study, neither our own data nor the evidence from previously published reports (see Introduction) permit the conclusion that a reduced or reversed laterality effect is more common in left-handed people. Footedness, earedness and overall congruency were also not significantly related to visual field or ear advantage. Thus, while these subject variables may be somewhat predictive of language laterality (see Introduction), they do not provide relevant information regarding non-verbal lateralization, at least in normal people. Surprisingly, eye preference was the variable most closely related to visual field asymmetry. The explanation for the linkage is not certain. It is unlikely that the findings are due to artifact caused by the presence of monocular suppressors (Bryden, 1982). According to this argument, monocular suppressors are people who typically use one eye even though both are functional. Given the superiority of the crossed pathways (Kruper, Patton and Koskoff, 1971) and the effects of cerebral dominance, one would expect a large LVF superiority in the left-eyed subjects and little or no LVF advantage in the right-eyed subjects. However, the reverse situation obtained here. Right-eyed subjects showed a LVF advantage and left-eyed subjects showed a bias towards the RVF. Moreover, the same pattern of results emerged in the auditory task. Eye preference was the best predictor of perceptual asymmetry. People who preferred the right eye were more likely than their left-sided counterparts to show a LEA.

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We are left with the possibility that eye preference is indeed related either directly or secondarily to non-verballateralization. It is important to note however, that knowledge of a person's eye preference does not allow for a very accurate prediction (10 to 20 percent) of perceptual asymmetry on non-verbal tasks. Nonetheless, the data reported here indicate that eye preference should be taken into account in future laterality studies in the non-verbal domain. ABSTRACf

The goal of the present study was to determine if, in a normal population, handedness, footedness, eyedness, earedness and overall congruency across lateral preferences were predictive of perceptual asymmetry on non-verbal tasks. In Experiment 1, subjects had to decide whether a laterally presented facial expression matched a previously presented target. In Experiment 2, subjects had to determine whether the tone of voice heard on dichotic and binaural presentations was the same or different. Eye preference was the most successful variable in predicting both visual field and ear advantages. Knowledge of a person's eye preference however, did not allow for a very accurate prediction of perceptual asymmetry. Nonetheless, the findings suggest that eye preference should be taken into account in future non-verbal laterality studies. Acknowledgement. This research was supported by grant N. A7933 from the N aturalcSciences and Engineering Research Council, Canada. REFERENCES

ANNETI, M. Handedness. In J.G. Beaumont (Ed.), Divided Visual Field Studies of Cerebral Organization. London: Academic Press, 1982. BRYDEN, M.P. Perceptual asymmetry in vision: Relation to handedness, eyedness, and speech lateralization. Cortex, 9: 418-435, 1973. BRYDEN, M.P. Laterality: Functional Asymmetry in the Intact Brain. New York: Academic Press, 1982. EKMAN, P., and FRIESEN, W.V. Measuring facial movement. Journal of Environmental Psychology and Nonverbal Behavior, 1: 56-75, 1975. HARDYCK, C., and PETRINOVITCH, L.F. Left-handedness. Psychological Bulletin, 84: 385404, 1977. HECAEN, H., DE AGOSTINI, M., and MONZON-MoNTES, A Cerebral organization in left-handers. Brain and Language, 12: 261-284, 1981. KRUPER, D.C., PATION, R.A, and KOSKOFF, Y.D. Hand and eye preference in unilaterally brain ablated monkeys. Physiology and Behavior, 7: 184-186, 1971. LEVY, J., and GUR, R.C. Individual differences in psychoneurological organization. In J. Herron (Ed.). Neuropsychology of Left-handedness. New York: Academic Press, 1980. LEY, R., and SRAUSS, E. Hemispheric asymmetries in the perception of facial expression by normals. In R. Bruyer (Ed.), The Neuropsychology of Face Perception and Facial Expression. New York: Lawrence Erlbaum, 1986. MASURE, M.e., and BENTON, AL. Visuospatial performance in left-handed patients with unilateral brain lesions. Neuropsychologia, 21: 179-181, 1983.

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PORAC, c., and COREN, S. Lateral Preferences and Human Behavior. New York: SpringerVedag, 1981. RASMUSSEN, T., and MILNER, B. The role of early left-brain injury in determining lateralization of cerebral speech functions. Annals of the New York Academy of Sciences, 299: 355-369, 1977. SATZ, P. Incidence of aphasia in left-handers: A test of some hypothetical models of cerebral speech organization. In J. Herron (Ed.), Neuropsychology of Left-handedness. New York: Academic Press, 1980. SAXBY, L., and BRYDEN, M.P. Left-ear superiority in children for processing auditory emotional material. Dev. Psycho!., 20: 72-80, 1984. SEARLEMAN, A. Subject variables and cerebral organization for language. Cortex, 16: 239-254, 1980. STRAUSS, E., and WADA, J. Lateral preferences and cerebral speech dominance. Cortex, 19: 165-177, 1983. STRAUSS, E. Hand, foot, eye and ear preferences and performance on a dichotic listening test. Cortex, 22, 475-482, 1986 TZAVARAS, A., HECAEN, H., and LEBRAS, H. Troubles de la reconnaissance du visage humain as lateralization hemispheriques lesionelle chez les subjet gauchers. Neuropsychologia, 9: 474-477, 1971. WHITE, M.J. Laterality differences in perception. Psychological Bulletin, 72: 387-405, 1969. WILLIAMS, S. Dichotic lateral asymmetry: The effects of grammatical structure and telephone usage. Neuropsychologia, 20: 457-464, 1982. E. Strauss, Ph.D., Dept. Psychology, Univ. Victoria, Victoria, British Columbia, Canada V8W 2Y2