Perceptual and Motor Skills, 1977,44, 1115-1122.

@ Perceptual and Motor Skills 1977

LATERAL EYE MOVEMENTS DURING VERBAL A N D NONVERBAL DICHOTIC LISTENING1 ESTHER LEFEVRE, RICHARD STARCK, WALLACE E. LAMBERT AND FRED GENESEE McGill Usiuersity Summary.-A dichotic listening paradigm was used to study the relation of eye movement to cerebral lateralization. The eye movements of right-handed

subjects were recorded during verbal and nonverbal dichotic-listening tasks. Subjects given a verbal dichotic-listening task made significantly more rightward than leftward eye movements and showed more accuracy and speed in processing information presented to the right than to the left ear. Subjects given a nonverbal dichotic-listening task made significantly more leftward eye movements and processed better information presented to the left ear. These findings suggest a potentially strong link between the direction of lateral eye movement during dichotic listening tasks and left- and right-ear advantages in performance on such tasks They also suggest that both eye movement and ear performance may be related to cerebral lateralicy and when examined in combination both could provide valuable information for the further study of hemispheric specialization. Teitelbaum (1954) first brought to attention the interesting fact that during periods of mental concentration people often spontaneously move their eyes in a leftward or rightward direction. Since then "lateral eye movements" during mental .reflection have been investigated clinically by Day ( 1964, 1967a, 1967b, 1968, 1970) and experimentally by a large number of researchers (for example, Bakan, 1969, 1971; Bakan & Strayer, 1973; Duke, 1968; Libby, 1970; Weiten & Etaugh, 1973) who have found that a person, when asked questions requiring mental reflection, tends to move his eyes consistently either to the right or to the left. It has been established that eye movements are controlled by activity in the contralateral frontal lobes of the brain in such a way that stimulation of the "frontal eye fields" of one hemisphere results in eye movement contralateral in direction to the hemisphere stimulated (Robinson, 1968). On this basis Bakan (1969, 1971) and Kinsbourne (1972, 1974) have proposed that lateral eye movement during reflection indicates generalized activation of a particular cerebral hemisphere, the one contralateral to the direction of eye movement. Specifically Kinsbourne (1972, 1973, 1974) reasons that cognitive neural acrivity in the brain during reflection results in an "overflow" of neural activity into the lateral-orientation control system or frontal eye fields. Thus activation of the functions of predominantly one hemisphere will cause an overflow of neural 'This research was supported in part by a grant from The Canada Council to W. E Lambert and G . R. Tucker.

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activity into the orientation control system of the same hemisphere, resulting thereby in eye movement contralateral in direction to the hemisphere activated. If both hemispheres are activated equally during reflection, both frontal lobes are stimulated equally and hence the eyes gaze straight ahead. Bakan (1969, 1971) has suggested that lateral eye movement during reflection may indicate a tendency for the hemisphere contralateral to the preferential direction of eye movement to be more easily activated. Bakan suggests that easier activation of one hemisphere may be related to, an individual preferential cognicive strategy, for example, a verbal versus a visuo-spatial approach to problem solving. Studies that support this interpretation have appeared. For example, "left-lookers" perform better than "right-lookers" on functions controlled by the right hemisphere while right-lookers perform better than leftlookers on functions controlled by the left hemisphere (Bakan, 1969; Harnad, 1972; Weiten & Etaugh, 1974). Apparently a person with a particular hernisphere preference for cognitive processing should be better at tasks relying on the use of that hemisphere's functions. Ocher studies have found the direction of lateral eye movement in righthanded persons to be determined in large part by the type of questions asked. Attempts to elicit lateral eye movement, using questions designed to engage one hemisphere or the other, have demonstrated thac right-handed subjects make more rightward eye movements in response to "left hemisphere," i.e., verbal, questions than to "right hemisphere," i.e., spatial or musical, questions and vice versa (Galin & Ornstein, 1974; Kinsbourne, 1972; Kocel, Galin, Ornstein, & Merrin, 1972; Weiten & Etaugh, 1974). These findings are consistent with the experimental evidence for lateralization of cognitive functioning at the same time as they provide support for the hypothesis that the direction of lateral eye movement during mental tasks reflects the concurrent activation of the contralateral cerebral hemisphere. In order to relate movement to lateralized activity one must first establish with as much certainty as possible the focus of cognicive processing, e.g., left versus right hemisphere, that is elicited by the task. The dichotic listening technique might be a more effective method chan thac used in previous studies since the dichotic listening procedure can be used to establish empirically the locus of cerebral processing, at least with respect to the left versus right hemisphere distinction. The dichotic presentation of sequential pairs of spoken digits typically activates the processing faculties of the left hemisphere just as the dichotic presentation of sequential pairs of environmental sounds or of melodies activates the faculties of the right hemisphere. This asymmetric hemispheric involvement in verbal and nonverbal processes is reflected in superiority of the right-ear performance, both in terms of priority and accuracy, in the recall of verbal scimuli and a superioricy of the left-ear performance in the recognition

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and recall of environmental sounds and melodies, i.e., nonverbal stimuli (Bryden, 1963; Curry, 1967; Curry 8: Rutherford, 1967; Kimura, 1961, 1964, 1967). The purpose of the present study was to determine whether the direction of lateral eye movement is related to asymmetrical hemispheric activity as indicated by a conventional mode of indexing cerebral lateralization, i.e., the dichotic listening paradigm. Ic was hypothesized that, if the predominant activation of one hemisphere results in lateral eye movement contralateral to the activated hemisphere, then the dichotic presentation of verbal stimuli should produce a predominance of rightward eye movements while the dichotic presentation of nonverbal stimuli should produce a predominance of leftward eye movements. ~ T H O D

Subjects Two groups of 20 subjects each were tested, one with a verbal (digits) dichotic listening task and the second with a nonverbal (environmental sounds) dichotic listening task. Each group induded 10 male and 10 female Englishspeaking right-handed undergraduates with normal hearing. Appa~atusand Terting Muter& The verbal tape was comprised of 10 sets of numbers, three pairs to a set. To prepare the tape, 5 three-pair sets of numbers were recorded on a tape in an IAC 11-148 soundtreated room, using a Sony TC-654-4 quadriadic tape recorder. Each stimulus pair was matched for intensity and stimulus onset by passing each pair of numbers through a Tekuonix type Rm-564 calibrated storage oscilloscope. There was a .5-sec. intra-stimulus interval between each pair and a 10-sec. intertrial interval between three-pair sets. Using a Dolby recording system, the two channels of the tape were crossed and the five sets of triple pairs were recorded again, but this time on opposite channels. Thus, a total of 10 sets of triple pairs was included on the verbal tape. The stimulus words were monosyllabic numbers, 1 through 10 excluding the digit 7. These were so combined that each pair consisted of two different numbers; all numbers occurred on the tape with equal frequency; and each number occurred equally often in each ear. A nonverbal dichotic tape consisting of 10 single pairs of environmental sounds was composed in the same manner. Each sound was of 4-sec. duration with a 10-sec. intertrial interval. The 10 single pairs of environmental sounds were recorded on tape and then recorded once more but on opposite channels, making a total of 20 single pairs of matched environmental sounds. The Dolby recording system was used to cross the two channels as previously described. The stimuli included the following types of sounds: a crow, a train whistle, bird song, applause, telephone dialing, dock ticking, dog barking, sawing, cat meowing, laughter, hammering, door creaking, thunder, children at play, horses galloping, coughing, cow, footsteps, car engine rewing, and motorized bicycle.

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Procedure Subjects were tested individually in a private experimental room seated at a table 3 ft. from the experimenter. For the verbal dichocic listening task, subjects were told that they would be listening through earphones to 10 three-pair sets of numbers with two different numbers presented simultaneously, one to each ear. They were to listen to all three pairs of numbers in each set and to repeat out loud as many of the six digits as possible in any order in the 10-sec. intertrial interval following each set. For the nonverbal task, subjects were informed that they would be hearing 20 single pairs of environmental sounds, each pair separated by a 10-sec. intertrial interval during which they were to identify the two sounds they had just heard. A two-channel stereo tape recorder with stereophonic earphones was used to present the stimuli. All verbal responses given during the 10-sec. intertrial interval were recorded on a cassette tape recorder. Headset position was counterbalanced across subjects so that half had the earphones in the "normal" position, i.e., channel 1 in the right ear, and half had them in the "reversed" position, i.e., channel 1 in the left ear. T o facilitate the experimenter's observation of eye movements the subjects' head movements were restricted: they were instructed to place their elbows on the table and to support their heads on their hands; they were not to move their heads but to face directly toward the experimenter. N o explanation was given for this procedure. At the end of the experimental session the subjects were questioned about its purpose, and none had guessed the real reason. The experimenter monitored the presentation of stimuli through earphones which facilitated the observation and recording of the direction of eye movements. For the verbal task only the initial movement, that following immediately after the onset of the first stimulus pair, was recorded for each of the 10 sets of digits. For the nonverbal task a record was kept of initial movements following the immediate onset of each of the 20 sets of single pairs of environmental sounds. Thus the presentation of each set of single pairs comprised one trial for the nonverbal task while the presentation of each set of triple pairs comprised one trial for the verbal task. An eye movement was defined as any lateral saccadic sweep of the eyes, i.e., gaze shift, made in either a leftward or rightward direction, regardless of where the subject's eyes were fixated (in the left, center, or right visual field) prior to the time of movement. Movements were clear in direction and easily distinguished from nonmovements. Trials in which the subject's eyes did not move following stimulus presentation were scored with a zero. W e decided against having subjects fixate their eyes straight ahead prior to each trial since previous studies have shown that asking subjects to fixate their gaze on some central point decreased substantially the number of lateral eye movements (Kinsbourne, 1974; Van Mastrigt & Sutter,

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1975 ) . Kinsbourne ( 1974) also suggests that making subjects consciously aware that their eye movements are being observed may confound results. Calcalation of Eye-mouement Scores By paying attention to initial eye movements only, there were 10 possible lateral movements for the verbal dichotic listening task and 20 possible movements for the nonverbal dichotic listening task. Percentage scores were calculated for the number of rightward, leftward or no movements made out of the total possible. Because there were few cases of no movement, the more left movements there were the fewer right movements there could be. Thus left and right movements were not independent, and for statistical analyses, the percentage of leftward movements only was used. These scores could range from 0 if only rightward movements occurred to 100 if only leftward movements occurred. Calculation of Scorer for Ear Performance Two measures of ear of input dominance were taken: accuracy of recall and order of recall. Accuracy of performance on each task was determined by calculating, independently for each ear of input, the proportion of stimuli accurately recalled out of the total number of stimuli presented to that ear. These proportion scores were then transformed into percentages. For order of recall there were 10 verbal trials and 20 nonverbal. Accordingly, order of recall scores on the nonverbal task were determined by calculating the number of left ear and right ear input stimuli mentioned first, providing us with a proportion of the total number of input stimuli correctly recalled "first." This procedure yielded separate right-ear and left-ear scores but unlike the two accuracy of recall scores the order of recall scores for the nonverbal task were not independent of one another, i.e., the two percentage scores add to 100%. Thus for purposes of statistical analysis, only one score was used. On the verbal task the order of recall measure was based on the first three stimuli which were correctly reported on each trial. The proportion of these stimuli which had been presented to the left ear and to the right ear were calculated separately. Only "right-ear scores" were analyzed statistically. All scores, eye movement and ear, were transformed using an arc sine transformation in order to normalize their distributions.

RESULTS Ear Preferences Independent analyses of variance were performed on the accuracy and order of recall scores. There were four factors involved in the accuracy of recall scores: task (verbal, nonverbal), sex (male, female), headset position (normal, reversed), and ear of input (right, left). A significant interaction of task by ear was found: on the verbal task, accuracy of recall was greater for right-ear

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( M = 2.39k.34) than left-ear inputs ( M = 2.16+-.do), while on the nonverbal task, accuracy of recall was greater for left-ear ( M = 2.32k.43) than right-ear inputs ( M = 2.20k.36; F1.32= 7.31, P < .05). A three-way analysis of variance was performed on the order of recall scores for right-ear preference. The independent variables in this analysis were: task (verbal, nonverbal), sex (male, female), and headset position (normal, reversed). A significant main effect was found for the task variable: stimuli presented to the right ear were recalled first more often during the verbal ( M = 1 . 6 8 k.26) than the nonverbal ( M = 1.38k.34) dichotic listening tasks (F1,32 = 9.85, p .01). Since the scores for left- and right-ear orders of recall were not independent, it follows that stimuli presented to the left ear were recalled first more often during the nonverbal task than during the verbal task. A calculation of the average left-ear order-of-recall scores for the verbal and nonverbal tasks substantiates this, verbal: 1.47 and nonverbal: 1.76. There were no other significant main effects or interactions in either of these analyses.

Lateral eye movements during verbal and nonverbal dichotic listening.

Perceptual and Motor Skills, 1977,44, 1115-1122. @ Perceptual and Motor Skills 1977 LATERAL EYE MOVEMENTS DURING VERBAL A N D NONVERBAL DICHOTIC LIS...
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