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Event-Related Potentials and Reaction Times as Measures of Hemispheric Differences for Physical and Semantic Kanji Matching
EVENT-RELATED POTENTIALS AND REACTION TIMES AS MEASURES OF HEMISPHERIC DIFFERENCES FOR PHYSICAL AND SEMANTIC KANJI MATCHING Takeshi Hatta, Yumiko Honjoh, and Hideki Mito1 (Osaka University of Education, Kwansei Gakuin University, and Kinki University Medical School)
I t is well known that the syndrome referred to as Gogi (semantic-form) aphasia is demonstrated in Japanese people who rely on two different types of character (Kanji, ideographic symbols, and Kana, phonetic symbols) in their orthography (lmura, Noguchi and Asakawa, 1971; Sasanuma, 1974). In Gogi aphasia, for example, patients make more errors in Kana word recognition while making significantly fewer errors in Kanji word recognition (Sasanuma and Fujimuni, 1971). The symptoms suggest that readings of Kanji and Kana characters are neurologically distinct. Consistent with these clinical reports, behavioural experimental evidence suggests that different types of hemispheric engagement might occur between Kanji and Kana recognition. Sasanuma, Itoh, Mori and Kobayashi (1977) reported that normal subjects showed right visual field superiority (left hemisphere superiority) in nonsense Kana word reading while they showed a stronger, though not significant, tendency toward left visual field superiority (right hemisphere superiority) in nonsense Kanji reading. Hatta (1977) also found a significant left visual field superiority for single Kanji recognition. Since Sasanuma and Hatta's reports, a wealth of evidence has been accumulated with behavioural measures which indicate that the reading of Kanji and the reading of Kana call for different patterns of hemispheric contribution (Hatta, 1978; Tzeng, Hung, Cotton and Wang, 1979; Hatta, 1981a). Recent reports in laterality influenced by the Stage Model in cognitive psychology, however, show that the features of hemispheric differences in character reading are more complex and less well understood than it was originally thought (Moscovitch, Scullion and Christie, 1976; Martin 1978). I
Author's names are noted in an alphabetical order.
Cortex (1983) 19, 517-528
518
Takeshi Hatta, Yumiko Honjoh, and Hideki Mito
In the Kanji recognition task, different types of hemispheric contributions have been suggested, based upon the levels of processing (Hatta, 1979; 1981a). For example, Hatta, using identical stimulus materials in two different experiments, reported that in an early stage of Kanji processing such as physical identity matching (experiment 1), subjects showed a left visual field advantage; but a right visual field advantage was found for the same stimuli in a deeper stage of Kanji processing such as in semantic congruency decisions (experiment 3). A number of studies have shown that Event-Related Potential (ERP) is a usuful measure for examining hemispheric functional asymmetries (Buchsbaum and Fedio, 1970; Thatcher, 1977; Neville, 1977). These studies have found that relatively complex verbal and non-verbal stimuli produce differential asymmetries in ERPs. Typically, larger amplitudes of ERPs are observed in the left hemisphere when the stimuli are verbal, while a right hemisphere effect has been reported for non-verbal stimuli. Such asymmetries, however, are not always found and they are often marginal (Shelbourne, 1973). Furthermore, even if ERPs reflect hemispheric differences in function, studies are prone to be criticised because of their recording method or statistical technique (Friedman, Simpson, Ritter and Rapin, 1975; Donchin, Rosen and McCarthy, 1977). Recent research seems to suggest that studies using ERP measures of laterality might not provide meaningful information (Beaumont and Mayes, 1977; Mayes and Beaumont, 1977), though a more optimistic view has been put forward (Hink, Kaga and Suzuki, 1980). If ERPs are reliable measures as mentioned above, electrophysiological recordings from subjects performing demanding cognitive tasks might yield convincing evidence of lateral functional asymmetries if these ERP measures correlate highly with such well demonstrated indices of laterality as R T and error rate. In addition, the behavioural mechanisms may be more fully understood if described from both a physiological and a behavioural point of view. Donchin, Rosen and McCarthy (1977) hypothesized that ERPs contain two components, exogeneous and endogenous; the former strongly relates to hemisphere asymmetry which is reflected by the nature of the stimulus material (e.g., verbal or non-verbal); the latter relates to the hemispheric asymmetry which is reflected by the stimulus processing modality. The present study was addressed to the latter component. The purpose of the present study was to examine whether human ERPs can be a useful measure in the study of laterality, especially in experimental studies which are influenced by cognitive psychology, e.g., Stage Model. More concretely, we were interested in the question of whether convincingly different ERP patterns can be found under two
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519
different stages of Kanji processing. That is, can ERPs from different hemispheric sites index two different stages of Kanji processing, Physical Identity Matching and Semantic Classification Matching?
MATERIALS AND METHOD
Subjects
Seven right-handed adults, 3 females and 4 males, age 21-26 served as subjects. Their handedness was assessed by the H.N. Handedness Inventory (Hatta and Nakatsuka, 1975). Stimuli
The stimulus material employed was identical to that of Hatta (1981 b). Stimuli consisted of 40 single Kanji characters. Each Kanji character subtended a visual ailgle of 0.68° x 0.68° and was projected 5.21 ° left or right from the centre of the visual field by a three-channel projector tachistoscope. Half of the Kanji were used as standard stimuli and the other half as target stimuli. Procedure
The following two tasks were given twice in ABBA order with task order counterbalanced across subjects. Physical Identity Matching
Each subject with electrode attached to the scalp sat at a table facing a translucent screen with his/her head supported by a chin-rest. For each trial, the subject was asked to fixate on the standard Kanji stimulus presented for 2 sec. at the centre of the screen. Then, the target Kanji was presented in the left or the right side of the visual field for 160 msec. The subject's task was to judge if the target was identical or not to the standard. The subject was asked to press, as quickly as possible, the "Yes" button if both were physically identical to each other and to press the "No" button if they were not. Subjects indicated their responses by pushing one of two buttons with either the index (Yes) or the middle finger (N 0) of one hand. In each group, both responding hand and the responding finger were randomized across subjects. After the 10-20 practice trials, which continued until improvement in response speed levelled off (a mean R T of less than 1000 msec. for 10 trials), subj ects were given a 5 minute resting period.
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Takeshi Hatta, Yumiko Honjoh, and Hideki Mito
Following the rest period, each subject was given a total of 80 trials. The inter-trial interval was 5 sec. Each subject was strongly urged to keep head and arm movement to a minimum. Semantic Classification Task.
The procedure was essentially identical with the Physical Identity Matching task. The only difference was that the subject was asked to judge if both the standard and the target Kanji fell into the identical categorical class, plant or animal. Following the practice trials, each subject was given 80 test trials. Recording and analysis
The EEG was recorded from C3 and C4 sites (the international 10-20 system), references to Al and A2 respectively. The electrooculogram (EOG) was recorded from infra- and supra-orbital electrodes placed about the left eye. Beckman biopotential scalp electrodes were used at all sites. The EEG was amplified with a SANEI Medical Telemeter 271 (band-pass 0.53-100 Hz) and stored along with trigger pulses on a TEAC cas set Data Recorder R70A for off-line analysis. ERPs were averaged separately across 72 (36 per run) of the target Kanji from each task with a signal processor (SANEI 7S06), and recorded with an X-Y recorder (Watanabe CX446). The analysis period was 400 ms (sampling rate 2 ms) beginning from the stimulus onset. The trials contaminated by excessive ocular or muscle activity were discarded. The peak-to-peak amplitudes of NI - PI> PI - N 2, N2 - P2, and P2 N 3 were taken. N I was defined as the first minumum voltage from stimulus onset. PI> N I> P2and N 3 were defined as the maximum and minimum voltage after N I, P b N2 and P2 respectively.
RESULTS
Behavioural Data
Figure 1 shows the mean R Ts of each experimental condition. ANOVA (Visual field X Type of task) revealed that the main effect f task type and the interaction were significant (Type of task: F = 9.52; 11 •• = 1,6; P <0.25; Interaction: F = 6.87; dJ. = 1,6; P <.25; Visual field: F = 1.36; dJ. = 1,6). These results indicate that RTs for the Semantic Classification task were longer than those for the Physical Identit' Matching task, and subjects showed quicker decisions when the targd Kanji appeared in the right visual field than in the left visual field for the Semantic Classification task, while there was no visual field difference for the Physical Identity Matching task.
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850
800 .......... If)
E
750
700 PHYSICAL IDENTITY
SEMANTIC C LASSIFICAT ION
Fig. 1 - Mean Reaction Times for Target Kanji Presented to the Left and Right Visual Fields in the Physical Identity and Semantic Classification Matching Tasks (Solid bar: Right VF and Open bar: Left VF).
The mean error rates of each experimental condition were as follows: In the Physical Identity Matching task: 4.4% (left visual field), 4.7% (right visual field). In the Semantic Classification task: 6.8% (left visual field),
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Takeshi Batta, Yumiko Bonjoh, and Bideki Milo
7.4% (right visual field). The errors were so few that statistical analyses could not be performed. Amplitudes of ERPs to the Target Kanji
The simultaneously recorded ERPs to the target Kanji did not show significant differences between the Physical Identity and Semantic Classification tasks. A complete set of ERPs from a typical subject is presented in Figure 2.
s
p
Fig. 2 - Event-related Potentials from the Right and Left Hemispheres of Subject H. Y. for the Physical Identity (P) and Semantic Classification Matching (S) Tasks (Solid line: C4> Dotted line: C3).
Subjects, though not all, had an early negative (33.1-71.3 ms; NI)positive (78.3-128.8 ms; PI) configuration. All subjects had the prominent negative (140-179.2 ms; N 2) configuration and several subjects had sustaining positive configuration (P2 and P3). From inspection of the ERP configuration, the following may be
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pointed out: (1) in a typical case, the N2 - P2 configuration for Physical Identity Matching was greater in C4 than in C 3. However, this tendency was not congruent among the subjects. Some had a greater N2 - P2in C4 for Physical Identity Matching and a greater N2 - P2 in C 3 for Semantic Classification, (2) A majority of subjects had a greater P 2 - N3 configuration in C 3 for the Physical Identity Matching task. Mean amplitudes and standard errors are shown in Table I.
TABLE I Mean Amplitudes (pY) and Standard Errors at the Left and Right Hemispheres in the Physical Identity and Sematic Classification Matching Tasks
Task Physical identity Semantic classification
Hemisphere Left Right Left Right
Mean SE Mean SE Mean SE Mean SE
NI - PI
PI - N2
N2 - P2
P2 - N3
5.55 2.93 5.46 2.46 5.14 1.98 4.91 2.55
10.36 3.62 11.41 2.54 11.03 2.04 11.50 2.15
7.96 2.91 7.91 3.43 7.34 3.09 8.37 2.93
2.83 2.66 4.10 3.89 2.88 2.95 2.94 2.05
A two-way ANOVA (Task X Hemisphere) was conducted for each amplitude. An ANOVA for NI - PI amplitude did not show any significant differences (Task: F = 0.67, dJ. = 1,6; Hemisphere: F = 0.07, dJ. = 1, 6; Interaction: F = 0.01 dJ. = 1,6). As for the PI - N 2, again, both main effects and interaction were nonsignificant (Task: F = 0.54, d.f. = 1,6; Hemisphere: F = 2.10, dJ. = 1, 6; Interaction: F = 0.32, d.f. = 1,6). However, an ANOVA for N2 - P2 configuration revealed a significant main effect of Hemisphere (F = 13.1: dJ. = 1,6; P <.001).1 The main effect of Task and the Interaction were not significant (Task: F = 0.01, dJ. = 1,6; Interaction: F = 1.16, dJ. = 1,6). An AN OVA for P2 - N3 showed a significant main effect of Hemisphere (F = 8.85; dJ. = 1,6; P <. 025), though the Task and the Interaction were not significant (Task: F = 1.57, dJ. = 1, 6; Interaction: F = 0.42 dJ. = 1, 6). These statistical analyses showed that the amplitudes of N2 - P 2and P2N3 were greater in the right hemisphere than in the left hemisphere. 1 In order to examine the effect of motor performance, another type of ANOVA, one-between and two-within (Task X Hemisphere X Button press hand), was conducted. Only the main effect of hemisphere was significant (F = 11.1; dJ. = 1,5; P <.025). The residual main effects and the interactions did not reach the significant level.
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TABLE II Mean Latencies (ms) and Standard Errors of Each Component in the Left and the Right H emisphere in the Physical Identity and Semantic Classification Tasks
Task Physical identity Semantic classification
Hemisphere Left Mean SE Mean Right SE Mean Left SE Mean Right SE
NI
PI
N2
P2
N3
59.9 12.9 52.7 15.4
99.7 15.7 106.9 16.7
51.5 9.2 51.9 10.8
105.9 16.5 109.6 11.3
164.7 6.7 164.8 12.9 167.9 6.6 169.0 11.3
246.2 17.8 245.3 20.5 265.2 16.5 265.5 11.5
328.6 42.2 331 .6 38.7 339.8 22.4 338.1 27.6
Latency of ERPs to the Target Kanji.
The mean latency for each component is shown in Table II. ANOVAs (Task X Hemisphere) were conducted separately for each component. Main effects and the Interactions were not significant for any component except for P2 where the main effect of Task was significant (F = 5.58; dJ. = 1, 6; P <.05). This single difference indicated that the P2 component was elicited earlier during Physical Identity Matching than during Semantic Classification. DISCUSSION
In the last two decades, many investigators have looked for evidence of differential hemispheric specialization using various kinds of stimulus materials, cognitive tasks, and cognitive modes of information processing. Generally speaking, though behavioural measures such as accuracy and speed have offered much evidence concerning human hemispheric functional asymmetries, ERP measures recorded from the left and right cerebral hemisphere have not yet yielded convincing evidence of specialization of hemispheric fucntion (Neville, 1980). Several studies have obtained positive results, i.e., greater ERP amplitudes from the left than the right hemisphere when verbal material is presented, and greater ERP amplitudes for the right than the left hemisphere when non-verbal material is presented (Neville, 1974; Molfese, Freeman and Palermo 1975; Hillyard and Woods, 1979), while other studies have reported no evidence for functional specialization in ERPs from the two hemispheres (Honjoh and Okita, 1981: Friedman et aI., 1975; Marsh and Thompson, 1973; Beaumont and Mayes, 1977; Mayes and Beaumont, 1977).
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Recent technological advances, however, permit to record ERPs continually and with a non-invasive monitoring of electro-physiological activity during the performance of cognitive task. If ERPs are sensitive enough, they may bring evidence to bear on models of the nature, sequencing, and timing of cognitive processes. That is, ERPs may allow us to reveal the correlation between electro-physiological and behavioural measures as well as the temporal structure of the cognitive processes. ERPs recorded when subjects perform demanding task might bring more convincing evidence of lateral functional asymmetries. It is likely that we can get the most convincing evidence that will relate to models of human information processing if both ERPs and other known behavioural indices of hemispheric asymmetries such as R T and error rate are in close agreement for subjects performing tasks requiring different stages of cognitive processing. Thus the present study examined the relationship between ERPs and behavioural measures for subjects performing tasks which have been shown to require lateralized function, i.e., tasks which produce lateral behavioural asymmetries. Especially, we were interested in whether ERPs show different types of patterns of asymmetry corresponding to different stages of processing for identical stimulus material. As mentioned before, Donchin et al. (1977) proposed two components, exogenous and endogenous, in ERPs. Coincident with their notion, Hink et al. (1980) observed different ERP asymmetry between Kanji and Kana recognition. They examined hemisphere differences in ERPs associated with reading Kanji and Hirakana and found that the lateral distributions of PI - NI to both characters differ from each other. However, based on Donchin's term, their experiment can be deemed as examining exogenous components of ERPs, not endogenous components. Therefore, as far as we know, the present experiment is the first to examine the endogenous components in ERPs associated with Kanji script processing. In the present experiment, we prepared two different stages of Kanji processing, Physical Identity Matching and Semantic Classification. The former involved an early stage of processing and the latter a late or deeper stage of processing (Moscovitch et aI., 1976; Hatta, 1981a). The results of asymmetry pattern in ERPs did not show any difference between the two tasks, i.e., the Task by Hemisphere interaction did not appear in any component, although in both tasks later components, N 2 P2 and P 2 - N3 showed asymmetrical amplitude differences between the left and right hemisphere. More concretely, amplitudes of ERPs at N2 - P2 and P2 - N3 were significantly greater in the right than in the left hemisphere. These findings seem to be coincident with the behavioural observation that the right
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hemisphere is more strongly engaged than the left hemisphere in single Kanji recognition (Hatta, 1977, 1978; Tzeng et aI., 1979). Behavioural data, on the other hand, were consistent with our expectation and were essentially identical with the findings of Hatta (Hatta, 1981 b). Reaction times showed a strongly significant interaction between the two types of task and the two visual fields. Subjects showed faster reaction times to the target Kanji in the right visual field in the Semantic Classification task, while no visual field difference was found in the Physical Identity Matching task. A suggestion similar to that advanced by Hatta (1981 b) can be made from the present behavioural data, that is, the left hemisphere contributes more in the semantic processing of verbal material while the right hemisphere is more involved in an early stage of processing. The findings of Ledlaw, Swanson and Kinsbourne (1978) can be regarded as being similar to those of our study. They conducted a Posnertype letter matching experiment and examined hemispheric differences using both behavioural (RTs) and electro-physiological (ERP) measures. As in the Posner-type paradigm different types of cognitive processing are required for matching the identical stimuli, their study can be regarded as an examination of endogenous components. ERPs and RTs were measured while the subjects performed name identity matching (e.g., Aa) and physical identity matching (e.g., AA). The results showed that RTs for stimuli to the right visual field were significantly faster than those of the left visual field in the name matching. ERP amplitudes showed the hemispheric asymmetry in the later component, P300 • However, the expected interaction of Type of Match x Visual Field was not observed, though the Type of Match by Visual Field interaction for P300 amplitude was significant for the left hemisphere. These results are similar to the present findings. In summary, from the comparison of the results of both ERPs and RTs in the present paradigm, it seems reasonable to draw a tentative conclusion that in the present experimental paradigm, ERPs do not index different hemispheric contributions of information processing, while behavioural measures seem sensitive enough to detect the asymmetries.
ABSTRACT
Hemispheric differences associated with Physical Identity Matching and Semantic Classification of Japanese characters (Kanji) were examined using visual event-related potentials and behavioural measures. Event-related potentials to the Kanji during matching tasks revealed hemispheric differences in the
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later components. Right hemisphere responses were larger than those or the left. The interaction of Types of Matches by Hemispheres was not significant. This interaction however was significant with the behavioural measure. On Semantic Classification Matching reaction times for right-visual-field Kanji were faster than those of the left field while no visual field difference was found for Physical Identity Matching. The sensitivity of both measures as indicators of laterality is discussed from the point of view of levels of processing. REFERENCES
BEAUMONT, G., and MAYES, A Do task and sex differences influence the visual evoked potential? Psychophysiology 14: 545-550, 1977. BUCHSBAUM M., and FEOIO, P. Hemispheric differences in evoked potentials to verbal and non-verbal stimuli in the left and right visual field. Electroencephalography and clinical Neurophysiology 26: 226-272, 1970. DONCHIN, E., ROSEN, S.C., and MCCARTHY, G. Electro-cortical indices of hemispheric utilization. In S. Hamad, R.W. Doty, L. Goldstein, J. Jaynes and G. Krauthamer (Eds.) Lateralization in the Nervous System, New York: Academic Press, 1977. FRIEDMAN, D., SIMPSON R., RITTER W., and RAPIN, I. Cortical evoked potentials elicited by real speech words and human sounds. Electroencephalography and clinical Neurophysiology 38: 13-19, 1975. HATTA, T. Recognition of Japanese Kanji in the left and right visual fields. Neuropsychologia 15: 685-688, 1977. HATTA T. Recognition of Japanese Kanji and Hirakana in the left and right visual fields. Japanese Psychological Research 20: 51-59, 1978. HATTA, T. Hemisphere asymmetries for physical and semantic congruency matching of visually presented Kanji stimuli. Japanese Journal of Psychology 50: 273-278, 1979. HATTA, T. Different stages of Kanji processing and their relations to functional hemisphere asymmetries. Japanese Psychological Research 23: 27-36, 1981a. HATTA, T. Task differences in the tachstoscopic Kanji recognition and their relations to hemispheric asymmetries. Japanese Journal of Psychology 52: 139-144, 1981b. HATTA, T., and NAKATSUKA, Z. H.N. Inventory. tn S. Ohno (Ed.) Papers in celebration of 63rd birthday of Prof Ohnishi. Osaka City University, 1975. HILLYARD S.A, and WOODS, D.D. Electrophysiological analysis of human brain function. In M. S. Gazzaniga (Ed.) Handbook of behavioral neurobiology, Vol. 2. New York: Plenum Press, 1979. HINK, R.F., KAGA, K., and SUZUKI, J. An evoked potential correlate of reading ideographic and phonetic Japanese scripts. Neuropsychologia 18: 455-464, 1980. HONJOH, Y., and OKITA, T. The effects of selective attention to tone pips and speech message upon event-related potentials. Japanese Journal of Psychology 52: 23-29, 1981. IMURA, T., NOGUCHI, Y., and ASAKAWA, A Aphasia in Japanese language. Nihon University Journal of Medicine 13: 69-90, 1971. LED LAW, A, SWANSON, J.M., and KINSBOURNE, M. Reaction times and evoked potentials as indicators of hemispheric differences to laterally presented name and physical matches. Journal of Experimental Psychology: Human Perception and Performance 4: 440-454, 1978. MARSH, G.R., and THOMPSON, L. W. Effects of verbal and non-verbal psychological set on hemispheric asymmetries in CNV. In W.C. McCallum and J. R. Knott (Eds.) Eventrelated slow potentials of the brain. Amsterdam: Elsevier, 1973. MARTIN, M. Hemispheric asymmetries for physical and semantic selection of visually presented words. Neuropsychologia 16: 717-724, 1978. MAYES A, and BEAUMONT, G. Does visual evoked potential asymmetry index cognitive activity? Neuropsychologia 15: 249-256, 1977.
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MOLFESE D.L., FREEMAN, R.B. Jr., and PALERMO, D.S. The ontogeny of brain lateralization of speech and non-speech stimuli. Brain and Language 2: 356-368, 1975. MOSCOVITCH, M., SCULLION, D., and CRlSTIE, D. Early versus late stages of processing and their relation to functional hemispheric asymmetries in face recognition. Journal of Experimental Psychology: Human Perception and Performance 2: 401-416, 1976. NEVILLE, H.J. Electrographic correlates of lateral asymmetry in the processing of verbal and nonverbal auditory stimuli. Journal od Psycholinguistic Research 3: 15-22, 1974. NEVILLE, H.J. Electrographic and behavioral cerebral specialization in congenitally deaf children: A preliminary report. In S. Segalowitz (Ed.), Language Development and Neurological Theory. New York: Academic Press, 1977. NEVILLE, H.J. Event-related potentials in neuropsychological studies of language. Brain and Language 11: 303-318, 1980. SASANUMA S. Kanji versus Kana processing in alexia with transient aphasia: A case report. Cortex 10: 89-97, 1974. SASANUMA, S., and FUJIMURA, O. Selective impairment of phonetic and non-phonetic transcription of words in Japanese aphasia patients: Kana vs. Kanji in visual recognition and writing. Cortex 7: 1-18, 1971. SASANUMA, S., ITOH, M., MORl, K., and KOBAYASHI, Y. Tachistoscopic recognition of Kana and Kanji words. Neuropsychologia 15: 547-553, 1977. SHELBOURNE, S.A. Jr. Visual evoked responses to language stimuli in normal children. Electroencephalography and clinical Neurophysiology 34: 135-143, 1973. THATCHER, R.W. Evoked potential correlates of hemispheric lateralization during semantic information processing. In S. Hamard, R.W. Doty, L. Golden, J. Jaynes, and G. Krauthamer (Eds.) Lateralization in the Nervous System. New York: Academic Press, 1977. TZENG, O.J.L., HUNG, D.L., COTTON, B., and WANG, W.S.Y. Visuallateralization effect in reading Chinese characters. Nature 282: 499-501, 1979. Dr. Takeshi Hatta, Dept. Psychology, Osaka University of Education, 43 Minamikawahori-cho, Tennoji-Ku, Osaka 543. JAPAN.
I t is well known that the syndrome referred to as Gogi (semantic-form) aphasia is demonstrated in Japanese people who rely on two different types of character (Kanji, ideographic symbols, and Kana, phonetic symbols) in their orthography (lmura, Noguchi and Asakawa, 1971; Sasanuma, 1974). In Gogi aphasia, for example, patients make more errors in Kana word recognition while making significantly fewer errors in Kanji word recognition (Sasanuma and Fujimuni, 1971). The symptoms suggest that readings of Kanji and Kana characters are neurologically distinct. Consistent with these clinical reports, behavioural experimental evidence suggests that different types of hemispheric engagement might occur between Kanji and Kana recognition. Sasanuma, Itoh, Mori and Kobayashi (1977) reported that normal subjects showed right visual field superiority (left hemisphere superiority) in nonsense Kana word reading while they showed a stronger, though not significant, tendency toward left visual field superiority (right hemisphere superiority) in nonsense Kanji reading. Hatta (1977) also found a significant left visual field superiority for single Kanji recognition. Since Sasanuma and Hatta's reports, a wealth of evidence has been accumulated with behavioural measures which indicate that the reading of Kanji and the reading of Kana call for different patterns of hemispheric contribution (Hatta, 1978; Tzeng, Hung, Cotton and Wang, 1979; Hatta, 1981a). Recent reports in laterality influenced by the Stage Model in cognitive psychology, however, show that the features of hemispheric differences in character reading are more complex and less well understood than it was originally thought (Moscovitch, Scullion and Christie, 1976; Martin 1978). I
Author's names are noted in an alphabetical order.
Cortex (1983) 19, 517-528
518
Takeshi Hatta, Yumiko Honjoh, and Hideki Mito
In the Kanji recognition task, different types of hemispheric contributions have been suggested, based upon the levels of processing (Hatta, 1979; 1981a). For example, Hatta, using identical stimulus materials in two different experiments, reported that in an early stage of Kanji processing such as physical identity matching (experiment 1), subjects showed a left visual field advantage; but a right visual field advantage was found for the same stimuli in a deeper stage of Kanji processing such as in semantic congruency decisions (experiment 3). A number of studies have shown that Event-Related Potential (ERP) is a usuful measure for examining hemispheric functional asymmetries (Buchsbaum and Fedio, 1970; Thatcher, 1977; Neville, 1977). These studies have found that relatively complex verbal and non-verbal stimuli produce differential asymmetries in ERPs. Typically, larger amplitudes of ERPs are observed in the left hemisphere when the stimuli are verbal, while a right hemisphere effect has been reported for non-verbal stimuli. Such asymmetries, however, are not always found and they are often marginal (Shelbourne, 1973). Furthermore, even if ERPs reflect hemispheric differences in function, studies are prone to be criticised because of their recording method or statistical technique (Friedman, Simpson, Ritter and Rapin, 1975; Donchin, Rosen and McCarthy, 1977). Recent research seems to suggest that studies using ERP measures of laterality might not provide meaningful information (Beaumont and Mayes, 1977; Mayes and Beaumont, 1977), though a more optimistic view has been put forward (Hink, Kaga and Suzuki, 1980). If ERPs are reliable measures as mentioned above, electrophysiological recordings from subjects performing demanding cognitive tasks might yield convincing evidence of lateral functional asymmetries if these ERP measures correlate highly with such well demonstrated indices of laterality as R T and error rate. In addition, the behavioural mechanisms may be more fully understood if described from both a physiological and a behavioural point of view. Donchin, Rosen and McCarthy (1977) hypothesized that ERPs contain two components, exogeneous and endogenous; the former strongly relates to hemisphere asymmetry which is reflected by the nature of the stimulus material (e.g., verbal or non-verbal); the latter relates to the hemispheric asymmetry which is reflected by the stimulus processing modality. The present study was addressed to the latter component. The purpose of the present study was to examine whether human ERPs can be a useful measure in the study of laterality, especially in experimental studies which are influenced by cognitive psychology, e.g., Stage Model. More concretely, we were interested in the question of whether convincingly different ERP patterns can be found under two
Hemispheric differences in classification of Kanji characters
519
different stages of Kanji processing. That is, can ERPs from different hemispheric sites index two different stages of Kanji processing, Physical Identity Matching and Semantic Classification Matching?
MATERIALS AND METHOD
Subjects
Seven right-handed adults, 3 females and 4 males, age 21-26 served as subjects. Their handedness was assessed by the H.N. Handedness Inventory (Hatta and Nakatsuka, 1975). Stimuli
The stimulus material employed was identical to that of Hatta (1981 b). Stimuli consisted of 40 single Kanji characters. Each Kanji character subtended a visual ailgle of 0.68° x 0.68° and was projected 5.21 ° left or right from the centre of the visual field by a three-channel projector tachistoscope. Half of the Kanji were used as standard stimuli and the other half as target stimuli. Procedure
The following two tasks were given twice in ABBA order with task order counterbalanced across subjects. Physical Identity Matching
Each subject with electrode attached to the scalp sat at a table facing a translucent screen with his/her head supported by a chin-rest. For each trial, the subject was asked to fixate on the standard Kanji stimulus presented for 2 sec. at the centre of the screen. Then, the target Kanji was presented in the left or the right side of the visual field for 160 msec. The subject's task was to judge if the target was identical or not to the standard. The subject was asked to press, as quickly as possible, the "Yes" button if both were physically identical to each other and to press the "No" button if they were not. Subjects indicated their responses by pushing one of two buttons with either the index (Yes) or the middle finger (N 0) of one hand. In each group, both responding hand and the responding finger were randomized across subjects. After the 10-20 practice trials, which continued until improvement in response speed levelled off (a mean R T of less than 1000 msec. for 10 trials), subj ects were given a 5 minute resting period.
520
Takeshi Hatta, Yumiko Honjoh, and Hideki Mito
Following the rest period, each subject was given a total of 80 trials. The inter-trial interval was 5 sec. Each subject was strongly urged to keep head and arm movement to a minimum. Semantic Classification Task.
The procedure was essentially identical with the Physical Identity Matching task. The only difference was that the subject was asked to judge if both the standard and the target Kanji fell into the identical categorical class, plant or animal. Following the practice trials, each subject was given 80 test trials. Recording and analysis
The EEG was recorded from C3 and C4 sites (the international 10-20 system), references to Al and A2 respectively. The electrooculogram (EOG) was recorded from infra- and supra-orbital electrodes placed about the left eye. Beckman biopotential scalp electrodes were used at all sites. The EEG was amplified with a SANEI Medical Telemeter 271 (band-pass 0.53-100 Hz) and stored along with trigger pulses on a TEAC cas set Data Recorder R70A for off-line analysis. ERPs were averaged separately across 72 (36 per run) of the target Kanji from each task with a signal processor (SANEI 7S06), and recorded with an X-Y recorder (Watanabe CX446). The analysis period was 400 ms (sampling rate 2 ms) beginning from the stimulus onset. The trials contaminated by excessive ocular or muscle activity were discarded. The peak-to-peak amplitudes of NI - PI> PI - N 2, N2 - P2, and P2 N 3 were taken. N I was defined as the first minumum voltage from stimulus onset. PI> N I> P2and N 3 were defined as the maximum and minimum voltage after N I, P b N2 and P2 respectively.
RESULTS
Behavioural Data
Figure 1 shows the mean R Ts of each experimental condition. ANOVA (Visual field X Type of task) revealed that the main effect f task type and the interaction were significant (Type of task: F = 9.52; 11 •• = 1,6; P <0.25; Interaction: F = 6.87; dJ. = 1,6; P <.25; Visual field: F = 1.36; dJ. = 1,6). These results indicate that RTs for the Semantic Classification task were longer than those for the Physical Identit' Matching task, and subjects showed quicker decisions when the targd Kanji appeared in the right visual field than in the left visual field for the Semantic Classification task, while there was no visual field difference for the Physical Identity Matching task.
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850
800 .......... If)
E
750
700 PHYSICAL IDENTITY
SEMANTIC C LASSIFICAT ION
Fig. 1 - Mean Reaction Times for Target Kanji Presented to the Left and Right Visual Fields in the Physical Identity and Semantic Classification Matching Tasks (Solid bar: Right VF and Open bar: Left VF).
The mean error rates of each experimental condition were as follows: In the Physical Identity Matching task: 4.4% (left visual field), 4.7% (right visual field). In the Semantic Classification task: 6.8% (left visual field),
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7.4% (right visual field). The errors were so few that statistical analyses could not be performed. Amplitudes of ERPs to the Target Kanji
The simultaneously recorded ERPs to the target Kanji did not show significant differences between the Physical Identity and Semantic Classification tasks. A complete set of ERPs from a typical subject is presented in Figure 2.
s
p
Fig. 2 - Event-related Potentials from the Right and Left Hemispheres of Subject H. Y. for the Physical Identity (P) and Semantic Classification Matching (S) Tasks (Solid line: C4> Dotted line: C3).
Subjects, though not all, had an early negative (33.1-71.3 ms; NI)positive (78.3-128.8 ms; PI) configuration. All subjects had the prominent negative (140-179.2 ms; N 2) configuration and several subjects had sustaining positive configuration (P2 and P3). From inspection of the ERP configuration, the following may be
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pointed out: (1) in a typical case, the N2 - P2 configuration for Physical Identity Matching was greater in C4 than in C 3. However, this tendency was not congruent among the subjects. Some had a greater N2 - P2in C4 for Physical Identity Matching and a greater N2 - P2 in C 3 for Semantic Classification, (2) A majority of subjects had a greater P 2 - N3 configuration in C 3 for the Physical Identity Matching task. Mean amplitudes and standard errors are shown in Table I.
TABLE I Mean Amplitudes (pY) and Standard Errors at the Left and Right Hemispheres in the Physical Identity and Sematic Classification Matching Tasks
Task Physical identity Semantic classification
Hemisphere Left Right Left Right
Mean SE Mean SE Mean SE Mean SE
NI - PI
PI - N2
N2 - P2
P2 - N3
5.55 2.93 5.46 2.46 5.14 1.98 4.91 2.55
10.36 3.62 11.41 2.54 11.03 2.04 11.50 2.15
7.96 2.91 7.91 3.43 7.34 3.09 8.37 2.93
2.83 2.66 4.10 3.89 2.88 2.95 2.94 2.05
A two-way ANOVA (Task X Hemisphere) was conducted for each amplitude. An ANOVA for NI - PI amplitude did not show any significant differences (Task: F = 0.67, dJ. = 1,6; Hemisphere: F = 0.07, dJ. = 1, 6; Interaction: F = 0.01 dJ. = 1,6). As for the PI - N 2, again, both main effects and interaction were nonsignificant (Task: F = 0.54, d.f. = 1,6; Hemisphere: F = 2.10, dJ. = 1, 6; Interaction: F = 0.32, d.f. = 1,6). However, an ANOVA for N2 - P2 configuration revealed a significant main effect of Hemisphere (F = 13.1: dJ. = 1,6; P <.001).1 The main effect of Task and the Interaction were not significant (Task: F = 0.01, dJ. = 1,6; Interaction: F = 1.16, dJ. = 1,6). An AN OVA for P2 - N3 showed a significant main effect of Hemisphere (F = 8.85; dJ. = 1,6; P <. 025), though the Task and the Interaction were not significant (Task: F = 1.57, dJ. = 1, 6; Interaction: F = 0.42 dJ. = 1, 6). These statistical analyses showed that the amplitudes of N2 - P 2and P2N3 were greater in the right hemisphere than in the left hemisphere. 1 In order to examine the effect of motor performance, another type of ANOVA, one-between and two-within (Task X Hemisphere X Button press hand), was conducted. Only the main effect of hemisphere was significant (F = 11.1; dJ. = 1,5; P <.025). The residual main effects and the interactions did not reach the significant level.
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TABLE II Mean Latencies (ms) and Standard Errors of Each Component in the Left and the Right H emisphere in the Physical Identity and Semantic Classification Tasks
Task Physical identity Semantic classification
Hemisphere Left Mean SE Mean Right SE Mean Left SE Mean Right SE
NI
PI
N2
P2
N3
59.9 12.9 52.7 15.4
99.7 15.7 106.9 16.7
51.5 9.2 51.9 10.8
105.9 16.5 109.6 11.3
164.7 6.7 164.8 12.9 167.9 6.6 169.0 11.3
246.2 17.8 245.3 20.5 265.2 16.5 265.5 11.5
328.6 42.2 331 .6 38.7 339.8 22.4 338.1 27.6
Latency of ERPs to the Target Kanji.
The mean latency for each component is shown in Table II. ANOVAs (Task X Hemisphere) were conducted separately for each component. Main effects and the Interactions were not significant for any component except for P2 where the main effect of Task was significant (F = 5.58; dJ. = 1, 6; P <.05). This single difference indicated that the P2 component was elicited earlier during Physical Identity Matching than during Semantic Classification. DISCUSSION
In the last two decades, many investigators have looked for evidence of differential hemispheric specialization using various kinds of stimulus materials, cognitive tasks, and cognitive modes of information processing. Generally speaking, though behavioural measures such as accuracy and speed have offered much evidence concerning human hemispheric functional asymmetries, ERP measures recorded from the left and right cerebral hemisphere have not yet yielded convincing evidence of specialization of hemispheric fucntion (Neville, 1980). Several studies have obtained positive results, i.e., greater ERP amplitudes from the left than the right hemisphere when verbal material is presented, and greater ERP amplitudes for the right than the left hemisphere when non-verbal material is presented (Neville, 1974; Molfese, Freeman and Palermo 1975; Hillyard and Woods, 1979), while other studies have reported no evidence for functional specialization in ERPs from the two hemispheres (Honjoh and Okita, 1981: Friedman et aI., 1975; Marsh and Thompson, 1973; Beaumont and Mayes, 1977; Mayes and Beaumont, 1977).
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Recent technological advances, however, permit to record ERPs continually and with a non-invasive monitoring of electro-physiological activity during the performance of cognitive task. If ERPs are sensitive enough, they may bring evidence to bear on models of the nature, sequencing, and timing of cognitive processes. That is, ERPs may allow us to reveal the correlation between electro-physiological and behavioural measures as well as the temporal structure of the cognitive processes. ERPs recorded when subjects perform demanding task might bring more convincing evidence of lateral functional asymmetries. It is likely that we can get the most convincing evidence that will relate to models of human information processing if both ERPs and other known behavioural indices of hemispheric asymmetries such as R T and error rate are in close agreement for subjects performing tasks requiring different stages of cognitive processing. Thus the present study examined the relationship between ERPs and behavioural measures for subjects performing tasks which have been shown to require lateralized function, i.e., tasks which produce lateral behavioural asymmetries. Especially, we were interested in whether ERPs show different types of patterns of asymmetry corresponding to different stages of processing for identical stimulus material. As mentioned before, Donchin et al. (1977) proposed two components, exogenous and endogenous, in ERPs. Coincident with their notion, Hink et al. (1980) observed different ERP asymmetry between Kanji and Kana recognition. They examined hemisphere differences in ERPs associated with reading Kanji and Hirakana and found that the lateral distributions of PI - NI to both characters differ from each other. However, based on Donchin's term, their experiment can be deemed as examining exogenous components of ERPs, not endogenous components. Therefore, as far as we know, the present experiment is the first to examine the endogenous components in ERPs associated with Kanji script processing. In the present experiment, we prepared two different stages of Kanji processing, Physical Identity Matching and Semantic Classification. The former involved an early stage of processing and the latter a late or deeper stage of processing (Moscovitch et aI., 1976; Hatta, 1981a). The results of asymmetry pattern in ERPs did not show any difference between the two tasks, i.e., the Task by Hemisphere interaction did not appear in any component, although in both tasks later components, N 2 P2 and P 2 - N3 showed asymmetrical amplitude differences between the left and right hemisphere. More concretely, amplitudes of ERPs at N2 - P2 and P2 - N3 were significantly greater in the right than in the left hemisphere. These findings seem to be coincident with the behavioural observation that the right
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hemisphere is more strongly engaged than the left hemisphere in single Kanji recognition (Hatta, 1977, 1978; Tzeng et aI., 1979). Behavioural data, on the other hand, were consistent with our expectation and were essentially identical with the findings of Hatta (Hatta, 1981 b). Reaction times showed a strongly significant interaction between the two types of task and the two visual fields. Subjects showed faster reaction times to the target Kanji in the right visual field in the Semantic Classification task, while no visual field difference was found in the Physical Identity Matching task. A suggestion similar to that advanced by Hatta (1981 b) can be made from the present behavioural data, that is, the left hemisphere contributes more in the semantic processing of verbal material while the right hemisphere is more involved in an early stage of processing. The findings of Ledlaw, Swanson and Kinsbourne (1978) can be regarded as being similar to those of our study. They conducted a Posnertype letter matching experiment and examined hemispheric differences using both behavioural (RTs) and electro-physiological (ERP) measures. As in the Posner-type paradigm different types of cognitive processing are required for matching the identical stimuli, their study can be regarded as an examination of endogenous components. ERPs and RTs were measured while the subjects performed name identity matching (e.g., Aa) and physical identity matching (e.g., AA). The results showed that RTs for stimuli to the right visual field were significantly faster than those of the left visual field in the name matching. ERP amplitudes showed the hemispheric asymmetry in the later component, P300 • However, the expected interaction of Type of Match x Visual Field was not observed, though the Type of Match by Visual Field interaction for P300 amplitude was significant for the left hemisphere. These results are similar to the present findings. In summary, from the comparison of the results of both ERPs and RTs in the present paradigm, it seems reasonable to draw a tentative conclusion that in the present experimental paradigm, ERPs do not index different hemispheric contributions of information processing, while behavioural measures seem sensitive enough to detect the asymmetries.
ABSTRACT
Hemispheric differences associated with Physical Identity Matching and Semantic Classification of Japanese characters (Kanji) were examined using visual event-related potentials and behavioural measures. Event-related potentials to the Kanji during matching tasks revealed hemispheric differences in the
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later components. Right hemisphere responses were larger than those or the left. The interaction of Types of Matches by Hemispheres was not significant. This interaction however was significant with the behavioural measure. On Semantic Classification Matching reaction times for right-visual-field Kanji were faster than those of the left field while no visual field difference was found for Physical Identity Matching. The sensitivity of both measures as indicators of laterality is discussed from the point of view of levels of processing. REFERENCES
BEAUMONT, G., and MAYES, A Do task and sex differences influence the visual evoked potential? Psychophysiology 14: 545-550, 1977. BUCHSBAUM M., and FEOIO, P. Hemispheric differences in evoked potentials to verbal and non-verbal stimuli in the left and right visual field. Electroencephalography and clinical Neurophysiology 26: 226-272, 1970. DONCHIN, E., ROSEN, S.C., and MCCARTHY, G. Electro-cortical indices of hemispheric utilization. In S. Hamad, R.W. Doty, L. Goldstein, J. Jaynes and G. Krauthamer (Eds.) Lateralization in the Nervous System, New York: Academic Press, 1977. FRIEDMAN, D., SIMPSON R., RITTER W., and RAPIN, I. Cortical evoked potentials elicited by real speech words and human sounds. Electroencephalography and clinical Neurophysiology 38: 13-19, 1975. HATTA, T. Recognition of Japanese Kanji in the left and right visual fields. Neuropsychologia 15: 685-688, 1977. HATTA T. Recognition of Japanese Kanji and Hirakana in the left and right visual fields. Japanese Psychological Research 20: 51-59, 1978. HATTA, T. Hemisphere asymmetries for physical and semantic congruency matching of visually presented Kanji stimuli. Japanese Journal of Psychology 50: 273-278, 1979. HATTA, T. Different stages of Kanji processing and their relations to functional hemisphere asymmetries. Japanese Psychological Research 23: 27-36, 1981a. HATTA, T. Task differences in the tachstoscopic Kanji recognition and their relations to hemispheric asymmetries. Japanese Journal of Psychology 52: 139-144, 1981b. HATTA, T., and NAKATSUKA, Z. H.N. Inventory. tn S. Ohno (Ed.) Papers in celebration of 63rd birthday of Prof Ohnishi. Osaka City University, 1975. HILLYARD S.A, and WOODS, D.D. Electrophysiological analysis of human brain function. In M. S. Gazzaniga (Ed.) Handbook of behavioral neurobiology, Vol. 2. New York: Plenum Press, 1979. HINK, R.F., KAGA, K., and SUZUKI, J. An evoked potential correlate of reading ideographic and phonetic Japanese scripts. Neuropsychologia 18: 455-464, 1980. HONJOH, Y., and OKITA, T. The effects of selective attention to tone pips and speech message upon event-related potentials. Japanese Journal of Psychology 52: 23-29, 1981. IMURA, T., NOGUCHI, Y., and ASAKAWA, A Aphasia in Japanese language. Nihon University Journal of Medicine 13: 69-90, 1971. LED LAW, A, SWANSON, J.M., and KINSBOURNE, M. Reaction times and evoked potentials as indicators of hemispheric differences to laterally presented name and physical matches. Journal of Experimental Psychology: Human Perception and Performance 4: 440-454, 1978. MARSH, G.R., and THOMPSON, L. W. Effects of verbal and non-verbal psychological set on hemispheric asymmetries in CNV. In W.C. McCallum and J. R. Knott (Eds.) Eventrelated slow potentials of the brain. Amsterdam: Elsevier, 1973. MARTIN, M. Hemispheric asymmetries for physical and semantic selection of visually presented words. Neuropsychologia 16: 717-724, 1978. MAYES A, and BEAUMONT, G. Does visual evoked potential asymmetry index cognitive activity? Neuropsychologia 15: 249-256, 1977.
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MOLFESE D.L., FREEMAN, R.B. Jr., and PALERMO, D.S. The ontogeny of brain lateralization of speech and non-speech stimuli. Brain and Language 2: 356-368, 1975. MOSCOVITCH, M., SCULLION, D., and CRlSTIE, D. Early versus late stages of processing and their relation to functional hemispheric asymmetries in face recognition. Journal of Experimental Psychology: Human Perception and Performance 2: 401-416, 1976. NEVILLE, H.J. Electrographic correlates of lateral asymmetry in the processing of verbal and nonverbal auditory stimuli. Journal od Psycholinguistic Research 3: 15-22, 1974. NEVILLE, H.J. Electrographic and behavioral cerebral specialization in congenitally deaf children: A preliminary report. In S. Segalowitz (Ed.), Language Development and Neurological Theory. New York: Academic Press, 1977. NEVILLE, H.J. Event-related potentials in neuropsychological studies of language. Brain and Language 11: 303-318, 1980. SASANUMA S. Kanji versus Kana processing in alexia with transient aphasia: A case report. Cortex 10: 89-97, 1974. SASANUMA, S., and FUJIMURA, O. Selective impairment of phonetic and non-phonetic transcription of words in Japanese aphasia patients: Kana vs. Kanji in visual recognition and writing. Cortex 7: 1-18, 1971. SASANUMA, S., ITOH, M., MORl, K., and KOBAYASHI, Y. Tachistoscopic recognition of Kana and Kanji words. Neuropsychologia 15: 547-553, 1977. SHELBOURNE, S.A. Jr. Visual evoked responses to language stimuli in normal children. Electroencephalography and clinical Neurophysiology 34: 135-143, 1973. THATCHER, R.W. Evoked potential correlates of hemispheric lateralization during semantic information processing. In S. Hamard, R.W. Doty, L. Golden, J. Jaynes, and G. Krauthamer (Eds.) Lateralization in the Nervous System. New York: Academic Press, 1977. TZENG, O.J.L., HUNG, D.L., COTTON, B., and WANG, W.S.Y. Visuallateralization effect in reading Chinese characters. Nature 282: 499-501, 1979. Dr. Takeshi Hatta, Dept. Psychology, Osaka University of Education, 43 Minamikawahori-cho, Tennoji-Ku, Osaka 543. JAPAN.