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The inferential interference effects of environmental sounds on spoken speech in Japanese and British people
BRAIN
AND
13, 241-249 (1981)
LANGUAGE
The Inferential Interference Effects of Environmental Sounds on Spoken Speech in Japanese and British People TAKESHI Department
of Psychology,
HATTA
Osaka University
of Education,
Japan
AND STUART Department
of Psychology,
J. DIMOND
University College, United Kingdom
Cardiff,
Wales University,
Spoken speech was paired with several kinds of environmental sounds and presented dichotically to both native Japanese and British subjects to compare the direction and degree of ear advantage. Results suggest that environmental sounds interfere in a similar manner for both groups of subjects but that there are highly significant differences in the degree of ear advantage between the Japanese and British subjects which might be due to some linguistic influences.
Cultural influences upon cerebral functional asymmetry, especially linguistic differences, have been examined in a number of studies. Walters and Zatorre (1978) examined laterality differences for word identification in bilinguals and reported that although Spanish-English bilinguals showed a right-visual-field advantage for the processing of both languages, more bilinguals as compared to monolinguals showed wide individual differences. From this, they suggested less unilaterality of language function in bilinguals than in monolinguals. Lhermitte, Hecaen, Dubois, Cullioli, and Tabouret-Keller (1966) also presented evidence indicating less marked hemisphere lateralization in polyglots, and Bever (1974) This study was conducted at the Department of Psychology, Osaka University of Education, Osaka, Japan, and the Department of Psychology University College, Cardiff, Cardiff, U. K. while the first author was working as an overseas research fellow supported by the Ministry of Education in Japan. Reprint requests should be sent to Takeshi Hatta, Department of Psychology, Osaka University of Education, 43 Minamikawahori-cho, Tennoji-ku, Osaka City 543, Japan. 241 0093-934X18l/O4024I -09$02.00/O Copyright 0 1981 by Academic Press, Inc. All rights of reprodwtkn in any form reserved.
242
HATTA AND DIMOND
reported a dichotic listening study with young Hispanic children in which the children showed a right-ear (left-hemisphere) advantage with respect to the first language whereas the second language did not exhibit any ear asymmetry. Scott, Hynd, Hunt, and Weed (1979) also reported that native American Navajo subjects showed a left-ear advantage while the wellknown right-ear effect was found in the Anglo subjects. Further, Van Lanker and Fromkin (1973) demonstrated in results from 22 native Thai (tone language) speakers that tone words and consonant words are better heard in the right ear, whereas English speakers showed no ear differences for tone words. All of these results suggest the possibility that linguistic differences may have an effect upon cerebral functioning, especially in the pattern and degree of interhemispheric functional asymmetry. The purpose of the present study therefore was to make cross-cultural comparison and to examine whether Japanese people have the same pattern of functional cerebral asymmetry for speech recognition as Westerners. Tsunoda (1975, 1977) reported several studies of laterality differences showing some functional differences between speakers of Indo-European language and speakers of Japanese. According to Tsunoda, animal sounds such as the songs of a bird, a dog barking, a cat mewing, or the croaking and chirping of a cricket were recognized dominantly in the right ear in the Japanese, but in the left ear in the Westerners. Although his method is a somewhat special one and does have some weakness in it (e.g., ambiguity of index definition of interference effect on tapping rhythms), this hypothesis is unique and is certainly one with deep implications. Therefore this experiment aimed to examine the appropriateness of Tsunoda’s proposal. To carry out the examination, spoken speech in the form of digit sequences was paired with several kinds of environmental sounds and presented dichotically to both Japanese and British subjects. The essential paradigm took the form of a cross-cultural comparison, half the experiment being conducted in the U. K. using native English speakers and other half in Japan using native Japanese speakers. METHOD
Subjects Forty-two volunteers from Osaka University of Education in Japan and University College, Cardiff in the U. K. participated in this experiment. Twenty-one (10 males and 11 females) were native Japanese speakers and another twenty-one (11 males and 10 females) were native English speakers. All were right-handed.
Stimuli Two categories of stimuli were employed: the first consisted of a six-digit random sequence spoken in English by a female voice and the second consisted of four kinds of environmental sounds or white noise. Six digits in each trial were spoken sequentially at the
CROSS-CULTURAL
COMPARISON
243
rate of one per second. The intertrial interval was about 10 sec. The second category of stimuli consisted of bird songs, a dog barking, insect sounds, traffic noise, and white noise. Stimuli from each category were recorded on a separate channel of a stereo tape recorder (Tandberg Model 12-41). Thirty trials of digit sequences and thirty of each kinds of sounds were recorded separately on each channel. The environmental sound channel was left on continuously during the trial. The two stimulus categories were delivered separately, one to each ear through a stereo tape recorder (Tandberg Model 12-41in U. K. and Sony stereo cassete coder TC 30000 SD in Japan). The qualities of the stimuli were as follows as determined using a Parsonal FFT Analyzer (Ono Sokki, Model CF-400): the intensity of the first category (speech) was 52.3 t 1.Odb SPL and frequency ranged from 100to 800 Hz. The intensities of the second category: of bird songs, a dog barking, insect sounds, traffic noise, and white noise were 43.6 ? 1.Odb, 48.9 t 1.0 db, 50.1 2 1.0 db, 50.0 + I.0 db, and 51.3 db, respectively. The frequencies of these stimuli ranged from 50 to 820 Hz with a peak of 190.5 Hz for bird songs, from 50 to 1400Hz with a peak of 522.5 Hz for dog barking, from 45 to 990 Hz with a peak of 130.0 Hz for insect sounds, and from 10 to 4600 Hz with a peak of 175 Hz for traffic noise.
Procedure The subjects were instructed that the experiment was designed to examine the effects of the interference of noise. They were informed that they would hear a digit sequence in one ear and noise in the opposite ear simultaneously. The task of the subjects was to write down the digit sequence they heard after each digit sequence presentation. The test session began with 10 practice trials. Each subject heard 15 digit sequences in each ear in each session of different environmental sounds. In the first 15 trials, spoken stimuli were delivered to one ear and in another 15 trials they were delivered to the opposite ear. Half the subjects heard spoken stimuli in the right ear first, and half in the left ear first. In the first test session, spoken stimuli were paired with white noise and in the second with bird songs. In the third session, spoken speech was paired with the sound of a dog barking and in the fourth session with insect sounds. In the final session spoken speech was paired with traffic noise. The order of the presentation of these sessions was identical in all subjects. Rest pauses of 5 min were given during the intersessional intervals. Overall, each subject heard 150 stimuli. For every subject, the headphones were reversed after the first half of the trial in each session to control for any disparity in the volume of the two channels. The experiment for British subjects was conducted from September to December 1977at the Department of Psychology, University College, Cardiff and for Japanese subjects during November and December 1978 at the Department of Psychology, Osaka University of Education.
RESULTS
The mean percentages of correctly recognized digit sequences in each presentation condition for Japanese and British students are shown in Table 1. Correct response refers to report all digits correctly in the correct order. An analysis of variance with repeated measures was conducted on these results with nationality of subjects as the between-subject factor, and digit presentation ear and the kinds of interference sounds as the within-subject factors. First, the main factors of digits presentation ear and the kind of interference sounds were both significant (F( 1,360) = 26.06, p < .OOl; F(4,160) = 14.37, p < .OOl, respectively), while the nationality of the subjects was
244
HATTA AND DIMOND TABLE 1
MEAN PERCENTAGE OF CORRECT RESPONSES IN EACH PRESENTATION CONDITION OF JAPANESE AND ENGLISH SUBJECTS
Spoken speech paired with
Nationality of subjects: Digit presentation:
White noise Bird song Dog barking Insect sound Traffic noise
Japanese
English
Left ear
Right ear
Left ear
Right ear
68.00 (13.79) 65.80 (13.51) 66.22 (18.42) 77.50 (17.27) 78.80 (15.50)
72.10 (14.99) 68.80 (16.29) 73.60 (17.06) 76.90 (17.88) 80.70 (16.20)
47.38 (13.84) 69.71 (12.88) 67.38 (12.52) 80.43 (10.80) 67.10 (14.62)
66.95 (22.40) 80.90 (14.18) 79.67 (13.44) 83.19 (14.47) 77.43 (14.80)
a SD are given in parentheses.
not significant (F( 1,40) = .006). The interaction of digit presentation ear X nationality of subjects was, however, highly significant (F(1,360) = 32.00, p < .OOl), whereas none of the other interactions reached a level of significance. Second, the results indicate that where spoken digits are presented to the right ear and environmental sounds to the left ear, performance is superior to that for the condition where these are reversed. Third, the mean correct responses were not similar for each different environmental sound. In other words, the interference effects of the various sounds differ depending upon their nature. Although the Japanese were less affected than the British by white noise, the performances under the condition in which spoken speech was paired with white noise taken overall were inferior in the sense of showing a greater amount of interference than did those under the other conditions (bird songs, t(166) = 2.91,~ < .Ol; dog barking, t(166) = 2.99,~ < .Ol; insect sounds, t(166) = 6.09, p < .OOl; traffic noise, t(166) = 4.59, p < .OOl) and the performances in the insect sounds condition were superior to those under the other conditions (white noise, t(166) = 6.09, p < .OOl; bird songs, t(166) = 3.57,~ < .OOl; dog barking, t(166) = 3.29,~ < .Ol), except that for traffic noise. Figure 1 shows these differences. Fourth, the significant interaction of digit presentation ear x nationality of the subjects indicates that the British students showed a strong right-ear digit presentation advantage (t(208) = 4.82, p < .OOl), whereas the Japanese did not show a significant asymmetry between the right- and left-ear digit presentation condition (t(208) = 1.41). DISCUSSION
In this experiment, spoken digits were paired with environmental sounds and presented dichotically to the subjects of the different cultures.
CROSS-CULTURAL
COMPARISON
245
90 : z
BO-
JAPANESE
ENGLISH
n r
? LR E BIRD SE SONG
[ LR DOG BARK
LR L R INSECT TRAFFIC SOUND NOISE
FIG. 1. Mean percentage of correct responses in each experimental conditions for Japanese and English subjects. (L: speech presented to the left ear; R: speech presented to the right ear).
To conduct these cross-cultural comparison strictly, it is essential to employ identical stimuli and conduct the experiment under the same experimental conditions with plural native populations who belong to different cultures. In this study spoken digits were employed because we deemed that digits spoken in English are used as a common language equally by British and Japanese students. There might be slight differences in the pronunciation but this we did not regard as a crucial factor. Japanese students are well accustomed to digits spoken in English and they easily recognize each digit spoken in English. This is apparent from the results of the study represented here, for the mean performance levels of both British and Japanese students did not differ. We can therefore regard this experiment as one which satisfies the essential conditions of cross-cultural comparison. The results of this experiment also are thought to reflect the intrinsic nature of the cerebral function of both groups of subjects. As shown in Fig. 1, the sounds interfered differentially with the recognition of spoken speech. The performance level overall with white noise was inferior to that under all other conditions; the performance with insect sounds was better than that under the other conditions. White noise covered all frequency bands, while the other sounds covered only limited bands of frequency. This might reflect the strongest interference effects
246
HATTA AND DIMOND
upon spoken-digit recognition. Insect sounds ranged from 45 to 990 Hz in frequency and have a monopolar peak at 130.0 Hz, while other environmental sounds have a multipolar frequency distribution. The band of frequency of speech ranged from 100 Hz with several peaks. These different properties of sounds might explain the various interference effects. According to the proposal of Tsunoda, Japanese people should show dominant recognition for animal sounds in the right ear and the Westerners dominant recognition in the left ear; it can be hypothesized therefore that for the Japanese, where spoken speech was presented from the right ear and environmental sounds presented from the left, both streams of information have to be processed in the left hemisphere. Then blocks to function should occur because each stream of information mutually interferes with the other, resulting in poor performance. For the British, on the other hand, the situation is different and here there should be a righthemisphere advantage in listening to environmental sounds and a lefthemisphere advantage in listening to verbal material. Under the condition where spoken speech was presented to the right ear and environmental sounds presented to the left, each hemisphere should be occupied with the processing of information to which it is best suited, and the performance should be better than that of the Japanese subjects. If the hypothesis of Tsunoda is correct, performance by the British subjects should be superior to that of the Japanese subjects in the animal sounds conditions. Furthermore, for the Japanese subjects, the interference effects of white noise and traffic noise should differ from those for animal sounds. Thus a significant interaction of digit presentation ear x kind of environmental sound and nationality of subjects was expected. As apparent from the results, the interaction of digit presentation ear x kind of environmental sounds x nationality of subjects was not significant (F(4,160) = 0.55) and this result did not support Tsunoda’s proposal. Again the fact that the performance of Japanese and British subjects under the condition where spoken digits were presented to the right ear did not differ significantly under any animal sounds conditions (bird song, t(20) = 0.94; dog barking, ~(20) = 0.23; insect sounds, t(20) = 0.64) does not support his proposal. Knox and Kimura (1970) demonstrated a left-ear (right-hemisphere) advantage in the recognition of environmental sounds with Westerners using dichotic listening. The present results suggest that both Japanese and British subjects processed environmental sounds and spoken speech in a similar manner because the Japanese as well as the British showed significantly superior recognition of spoken digits presented to the right ear than to the left ear (F(1,130) = 26.06, p < .OOl). This presumably reflects the fact that in right-ear speech presentation, the left hemisphere receives information about speech and the right-hemisphere receives other information about noise simultaneously; that is, each hemisphere
CROSS-CULTURAL
COMPARISON
247
must be occupied with the processing of information to which it is best suited. On the other hand, in the left-ear speech presentation condition, the left hemisphere receives the noise stimuli and the right hemisphere receives the spoken speech. Here each hemisphere must be occupied with the processing of information to which it is not so suited, then some interhemispheric transfer of both types of information might be necessary. Therefore, something like mutual interference of the two kinds of information and a decline of the signal to noise ratio in the course of interhemispheric transfer might occur. This might be the interpretation for the lower performance under the latter condition. The interaction of digit presentation ear x nationality of subjects revealed a highly significant effect (F( 1,360) = 32.00,~ < .OOl). As shown in Fig. 2, the mean percentage of correct recognition in the right-ear presentation condition of British subject was 77.6%, and 66.4% in the left-ear digit presentation. This right-ear digit presentation advantage was statistically significant (t(208) = 4.82,~ < .OOl). On the other hand, the Japanese subjects’ right-ear digit presentation condition was 74.4%, and 71.3% in the left-ear digit presentation. Though the trend toward right-ear digit presentation advantage was apparent, the difference did not. reach a significant level (t(208) = 1.41). This strongly suggests that the asymmetric specialization of hemisphere function of the British in the task where spoken speech was presented dichotically with simultaneous environmental noise is more marked than that of the Japanese. These results apparently support the notion that linguistic differences have an effect upon the cerebral functioning in the pattern and degree of interhemispheric functional asymmetry as well as in the results of dichotic-listening studies with polyglots (Lhermitte et al., 1966; Bever, 1974)and also in tachistoscopic studies (Orbach, 1967; Walters & Zattore, 1978). Recently, we conducted an experiment (Hatta & Dimond, 1980)
‘60 f LEFT
RIGHT DIGIT
FIG. 2. Mean percentage function of digit presentation
of correct ear.
PRESENTATION
EAR
responses of Japanese and English subjects as a
248
HATTA
AND DIMOND
which attempted to compare the pattern and degree of cerebral asymmetries in visual-recognition tasks between Japanese and British students. Verbal and nonverbal visual materials were presented to the left or the right visual field using Japanese and British students as subjects. The results with verbal materials indicated the same direction of laterality and a similar degree of specialization in both groups of subject; however, the results with nonverbal materials demonstrated that British students showed a highly significant left-visual-field superiority while the Japanese showed nonsignificant asymmetry. From these results, we proposed more bilateral hemisphere functioning in the Japanese. This significant interaction of digit presentation ear x nationality of subjects is in accordance with this proposal because the performance in the left-ear digit presentation condition of Japanese subjects was significantly superior to that of the British (t(208) =2.14, p < .OS), while no such differences appeared in the right-ear digit presentation condition between both groups of subject (t(208) = 1.40). The superior performance under the left-ear digit presentation condition of the Japanese subjects must be referred to the fact that the right hemisphere of the Japanese may contribute more in the processing of spoken speech than that of the British. The Japanese language is more vowel dependent than English, because vowels form meaningful monosyllabic words such as /a/ (mute, quasi), /i/ (stomach, medicine), /u/ (cormorant), /e/ (picture, food, handle), /o/ (tail, cord). It is said that consonants are significantly perceived dominantly in the left hemisphere while the right hemispl.?re contributes more in the processing of vowels (Shankweiler & Studdert-Kennedy, 1967). The Japanese language therefore could well demand stronger language representation in the right hemisphere than does the English language. Processing the Japanese language requires a more integrated action of both hemispheres than does processing English, and this might influence the different degree of ear asymmetry as shown in these results. This interpretation is a tentative one and we have to seek more germane evidence. However, from this experiment, we suggest first that environmental sounds are processed predominantly in the right hemisphere for both Japanese and British, unlike the proposal of Tsunoda (1975, 1977), and second that there are differences in cerebral asymmetry of auditory function, especially in degree rather than in direction, between the Japanese and British, and this might be due to some linguistic differences. REFERENCES Bever, T. 1974. The relation of language development to cognitive development. In E. Lenneburg (Ed.), Language and the bruin. Jamaica Plain, MA: Neuroscience Research Progress Bulletin. Curry, F. K. W. 1967. A comparison of left-handed and right-handed subjects on a verbal and nonverbal dichotic listening task. Correx, 3, 343-342.
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COMPARISON
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Hatta, T., & Dimond, S. J. 1980.Comparison of lateral differences for digit and random form recognition in Japanese and Westerners. Journal of Experimental Psychology: Human perception
and performance,
6, 368-374.
Knox, D., & Kimura, D. 1970. Cerebral processing of nonverbal sounds in boys and girls. Neuropsychologia,
8, 227-237.
Lhermitte, R., Hicaen, H., Dubois, J., Cullioli, A., & Tabouret-Keller, A. 1966. Le probleme de l’aphasie des polyglottes: Remarques sur quelques observation. Neuropsychologia, 4, 315-329. Orbach, J. 1967.Differential recognition of Hebrew and English words in right and left visual 5, fields as a function of cerebral dominance and reading habits. Neuropsychologia, 127-134. Scott, S., Hynd, G. W., Hunt, L., & Weed, W. 1979. Cerebral speech lateralization in the native American Navajo. Neuropsychologia, 17, 89-92. Shankweiler, D., & Studdert-Kennedy, M. 1967. Identification of consonants and vowels presented to left and right ears. Quarterly Journal of Experimental Psychology, 19, 59-63. Tsunoda, T. 1975. Functional differences between right and left cerebral hemispheres detected by the key-tapping method. Brain and Language, 2, 152-170. Tsunoda, T. 1977. Brain and language. In Y. Tanaka, S. Omori, & N. Sawada (Eds.), Languuge, consciousness and life, pp. l-3 1. Tokyo: Kyoritsu-syuppan. Van Lanker, D., & Fromkin, V. A. 1973. Hemispheric specialization for pitch and “tone”: Evidence from Thai. Journal of Phonetics, I, 101-109. Walters, J., & Zatorre, R. J. 1978. Laterality differences for words identification in bilinguals. Brain and Language, 6, 158-167.
AND
13, 241-249 (1981)
LANGUAGE
The Inferential Interference Effects of Environmental Sounds on Spoken Speech in Japanese and British People TAKESHI Department
of Psychology,
HATTA
Osaka University
of Education,
Japan
AND STUART Department
of Psychology,
J. DIMOND
University College, United Kingdom
Cardiff,
Wales University,
Spoken speech was paired with several kinds of environmental sounds and presented dichotically to both native Japanese and British subjects to compare the direction and degree of ear advantage. Results suggest that environmental sounds interfere in a similar manner for both groups of subjects but that there are highly significant differences in the degree of ear advantage between the Japanese and British subjects which might be due to some linguistic influences.
Cultural influences upon cerebral functional asymmetry, especially linguistic differences, have been examined in a number of studies. Walters and Zatorre (1978) examined laterality differences for word identification in bilinguals and reported that although Spanish-English bilinguals showed a right-visual-field advantage for the processing of both languages, more bilinguals as compared to monolinguals showed wide individual differences. From this, they suggested less unilaterality of language function in bilinguals than in monolinguals. Lhermitte, Hecaen, Dubois, Cullioli, and Tabouret-Keller (1966) also presented evidence indicating less marked hemisphere lateralization in polyglots, and Bever (1974) This study was conducted at the Department of Psychology, Osaka University of Education, Osaka, Japan, and the Department of Psychology University College, Cardiff, Cardiff, U. K. while the first author was working as an overseas research fellow supported by the Ministry of Education in Japan. Reprint requests should be sent to Takeshi Hatta, Department of Psychology, Osaka University of Education, 43 Minamikawahori-cho, Tennoji-ku, Osaka City 543, Japan. 241 0093-934X18l/O4024I -09$02.00/O Copyright 0 1981 by Academic Press, Inc. All rights of reprodwtkn in any form reserved.
242
HATTA AND DIMOND
reported a dichotic listening study with young Hispanic children in which the children showed a right-ear (left-hemisphere) advantage with respect to the first language whereas the second language did not exhibit any ear asymmetry. Scott, Hynd, Hunt, and Weed (1979) also reported that native American Navajo subjects showed a left-ear advantage while the wellknown right-ear effect was found in the Anglo subjects. Further, Van Lanker and Fromkin (1973) demonstrated in results from 22 native Thai (tone language) speakers that tone words and consonant words are better heard in the right ear, whereas English speakers showed no ear differences for tone words. All of these results suggest the possibility that linguistic differences may have an effect upon cerebral functioning, especially in the pattern and degree of interhemispheric functional asymmetry. The purpose of the present study therefore was to make cross-cultural comparison and to examine whether Japanese people have the same pattern of functional cerebral asymmetry for speech recognition as Westerners. Tsunoda (1975, 1977) reported several studies of laterality differences showing some functional differences between speakers of Indo-European language and speakers of Japanese. According to Tsunoda, animal sounds such as the songs of a bird, a dog barking, a cat mewing, or the croaking and chirping of a cricket were recognized dominantly in the right ear in the Japanese, but in the left ear in the Westerners. Although his method is a somewhat special one and does have some weakness in it (e.g., ambiguity of index definition of interference effect on tapping rhythms), this hypothesis is unique and is certainly one with deep implications. Therefore this experiment aimed to examine the appropriateness of Tsunoda’s proposal. To carry out the examination, spoken speech in the form of digit sequences was paired with several kinds of environmental sounds and presented dichotically to both Japanese and British subjects. The essential paradigm took the form of a cross-cultural comparison, half the experiment being conducted in the U. K. using native English speakers and other half in Japan using native Japanese speakers. METHOD
Subjects Forty-two volunteers from Osaka University of Education in Japan and University College, Cardiff in the U. K. participated in this experiment. Twenty-one (10 males and 11 females) were native Japanese speakers and another twenty-one (11 males and 10 females) were native English speakers. All were right-handed.
Stimuli Two categories of stimuli were employed: the first consisted of a six-digit random sequence spoken in English by a female voice and the second consisted of four kinds of environmental sounds or white noise. Six digits in each trial were spoken sequentially at the
CROSS-CULTURAL
COMPARISON
243
rate of one per second. The intertrial interval was about 10 sec. The second category of stimuli consisted of bird songs, a dog barking, insect sounds, traffic noise, and white noise. Stimuli from each category were recorded on a separate channel of a stereo tape recorder (Tandberg Model 12-41). Thirty trials of digit sequences and thirty of each kinds of sounds were recorded separately on each channel. The environmental sound channel was left on continuously during the trial. The two stimulus categories were delivered separately, one to each ear through a stereo tape recorder (Tandberg Model 12-41in U. K. and Sony stereo cassete coder TC 30000 SD in Japan). The qualities of the stimuli were as follows as determined using a Parsonal FFT Analyzer (Ono Sokki, Model CF-400): the intensity of the first category (speech) was 52.3 t 1.Odb SPL and frequency ranged from 100to 800 Hz. The intensities of the second category: of bird songs, a dog barking, insect sounds, traffic noise, and white noise were 43.6 ? 1.Odb, 48.9 t 1.0 db, 50.1 2 1.0 db, 50.0 + I.0 db, and 51.3 db, respectively. The frequencies of these stimuli ranged from 50 to 820 Hz with a peak of 190.5 Hz for bird songs, from 50 to 1400Hz with a peak of 522.5 Hz for dog barking, from 45 to 990 Hz with a peak of 130.0 Hz for insect sounds, and from 10 to 4600 Hz with a peak of 175 Hz for traffic noise.
Procedure The subjects were instructed that the experiment was designed to examine the effects of the interference of noise. They were informed that they would hear a digit sequence in one ear and noise in the opposite ear simultaneously. The task of the subjects was to write down the digit sequence they heard after each digit sequence presentation. The test session began with 10 practice trials. Each subject heard 15 digit sequences in each ear in each session of different environmental sounds. In the first 15 trials, spoken stimuli were delivered to one ear and in another 15 trials they were delivered to the opposite ear. Half the subjects heard spoken stimuli in the right ear first, and half in the left ear first. In the first test session, spoken stimuli were paired with white noise and in the second with bird songs. In the third session, spoken speech was paired with the sound of a dog barking and in the fourth session with insect sounds. In the final session spoken speech was paired with traffic noise. The order of the presentation of these sessions was identical in all subjects. Rest pauses of 5 min were given during the intersessional intervals. Overall, each subject heard 150 stimuli. For every subject, the headphones were reversed after the first half of the trial in each session to control for any disparity in the volume of the two channels. The experiment for British subjects was conducted from September to December 1977at the Department of Psychology, University College, Cardiff and for Japanese subjects during November and December 1978 at the Department of Psychology, Osaka University of Education.
RESULTS
The mean percentages of correctly recognized digit sequences in each presentation condition for Japanese and British students are shown in Table 1. Correct response refers to report all digits correctly in the correct order. An analysis of variance with repeated measures was conducted on these results with nationality of subjects as the between-subject factor, and digit presentation ear and the kinds of interference sounds as the within-subject factors. First, the main factors of digits presentation ear and the kind of interference sounds were both significant (F( 1,360) = 26.06, p < .OOl; F(4,160) = 14.37, p < .OOl, respectively), while the nationality of the subjects was
244
HATTA AND DIMOND TABLE 1
MEAN PERCENTAGE OF CORRECT RESPONSES IN EACH PRESENTATION CONDITION OF JAPANESE AND ENGLISH SUBJECTS
Spoken speech paired with
Nationality of subjects: Digit presentation:
White noise Bird song Dog barking Insect sound Traffic noise
Japanese
English
Left ear
Right ear
Left ear
Right ear
68.00 (13.79) 65.80 (13.51) 66.22 (18.42) 77.50 (17.27) 78.80 (15.50)
72.10 (14.99) 68.80 (16.29) 73.60 (17.06) 76.90 (17.88) 80.70 (16.20)
47.38 (13.84) 69.71 (12.88) 67.38 (12.52) 80.43 (10.80) 67.10 (14.62)
66.95 (22.40) 80.90 (14.18) 79.67 (13.44) 83.19 (14.47) 77.43 (14.80)
a SD are given in parentheses.
not significant (F( 1,40) = .006). The interaction of digit presentation ear X nationality of subjects was, however, highly significant (F(1,360) = 32.00, p < .OOl), whereas none of the other interactions reached a level of significance. Second, the results indicate that where spoken digits are presented to the right ear and environmental sounds to the left ear, performance is superior to that for the condition where these are reversed. Third, the mean correct responses were not similar for each different environmental sound. In other words, the interference effects of the various sounds differ depending upon their nature. Although the Japanese were less affected than the British by white noise, the performances under the condition in which spoken speech was paired with white noise taken overall were inferior in the sense of showing a greater amount of interference than did those under the other conditions (bird songs, t(166) = 2.91,~ < .Ol; dog barking, t(166) = 2.99,~ < .Ol; insect sounds, t(166) = 6.09, p < .OOl; traffic noise, t(166) = 4.59, p < .OOl) and the performances in the insect sounds condition were superior to those under the other conditions (white noise, t(166) = 6.09, p < .OOl; bird songs, t(166) = 3.57,~ < .OOl; dog barking, t(166) = 3.29,~ < .Ol), except that for traffic noise. Figure 1 shows these differences. Fourth, the significant interaction of digit presentation ear x nationality of the subjects indicates that the British students showed a strong right-ear digit presentation advantage (t(208) = 4.82, p < .OOl), whereas the Japanese did not show a significant asymmetry between the right- and left-ear digit presentation condition (t(208) = 1.41). DISCUSSION
In this experiment, spoken digits were paired with environmental sounds and presented dichotically to the subjects of the different cultures.
CROSS-CULTURAL
COMPARISON
245
90 : z
BO-
JAPANESE
ENGLISH
n r
? LR E BIRD SE SONG
[ LR DOG BARK
LR L R INSECT TRAFFIC SOUND NOISE
FIG. 1. Mean percentage of correct responses in each experimental conditions for Japanese and English subjects. (L: speech presented to the left ear; R: speech presented to the right ear).
To conduct these cross-cultural comparison strictly, it is essential to employ identical stimuli and conduct the experiment under the same experimental conditions with plural native populations who belong to different cultures. In this study spoken digits were employed because we deemed that digits spoken in English are used as a common language equally by British and Japanese students. There might be slight differences in the pronunciation but this we did not regard as a crucial factor. Japanese students are well accustomed to digits spoken in English and they easily recognize each digit spoken in English. This is apparent from the results of the study represented here, for the mean performance levels of both British and Japanese students did not differ. We can therefore regard this experiment as one which satisfies the essential conditions of cross-cultural comparison. The results of this experiment also are thought to reflect the intrinsic nature of the cerebral function of both groups of subjects. As shown in Fig. 1, the sounds interfered differentially with the recognition of spoken speech. The performance level overall with white noise was inferior to that under all other conditions; the performance with insect sounds was better than that under the other conditions. White noise covered all frequency bands, while the other sounds covered only limited bands of frequency. This might reflect the strongest interference effects
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HATTA AND DIMOND
upon spoken-digit recognition. Insect sounds ranged from 45 to 990 Hz in frequency and have a monopolar peak at 130.0 Hz, while other environmental sounds have a multipolar frequency distribution. The band of frequency of speech ranged from 100 Hz with several peaks. These different properties of sounds might explain the various interference effects. According to the proposal of Tsunoda, Japanese people should show dominant recognition for animal sounds in the right ear and the Westerners dominant recognition in the left ear; it can be hypothesized therefore that for the Japanese, where spoken speech was presented from the right ear and environmental sounds presented from the left, both streams of information have to be processed in the left hemisphere. Then blocks to function should occur because each stream of information mutually interferes with the other, resulting in poor performance. For the British, on the other hand, the situation is different and here there should be a righthemisphere advantage in listening to environmental sounds and a lefthemisphere advantage in listening to verbal material. Under the condition where spoken speech was presented to the right ear and environmental sounds presented to the left, each hemisphere should be occupied with the processing of information to which it is best suited, and the performance should be better than that of the Japanese subjects. If the hypothesis of Tsunoda is correct, performance by the British subjects should be superior to that of the Japanese subjects in the animal sounds conditions. Furthermore, for the Japanese subjects, the interference effects of white noise and traffic noise should differ from those for animal sounds. Thus a significant interaction of digit presentation ear x kind of environmental sound and nationality of subjects was expected. As apparent from the results, the interaction of digit presentation ear x kind of environmental sounds x nationality of subjects was not significant (F(4,160) = 0.55) and this result did not support Tsunoda’s proposal. Again the fact that the performance of Japanese and British subjects under the condition where spoken digits were presented to the right ear did not differ significantly under any animal sounds conditions (bird song, t(20) = 0.94; dog barking, ~(20) = 0.23; insect sounds, t(20) = 0.64) does not support his proposal. Knox and Kimura (1970) demonstrated a left-ear (right-hemisphere) advantage in the recognition of environmental sounds with Westerners using dichotic listening. The present results suggest that both Japanese and British subjects processed environmental sounds and spoken speech in a similar manner because the Japanese as well as the British showed significantly superior recognition of spoken digits presented to the right ear than to the left ear (F(1,130) = 26.06, p < .OOl). This presumably reflects the fact that in right-ear speech presentation, the left hemisphere receives information about speech and the right-hemisphere receives other information about noise simultaneously; that is, each hemisphere
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must be occupied with the processing of information to which it is best suited. On the other hand, in the left-ear speech presentation condition, the left hemisphere receives the noise stimuli and the right hemisphere receives the spoken speech. Here each hemisphere must be occupied with the processing of information to which it is not so suited, then some interhemispheric transfer of both types of information might be necessary. Therefore, something like mutual interference of the two kinds of information and a decline of the signal to noise ratio in the course of interhemispheric transfer might occur. This might be the interpretation for the lower performance under the latter condition. The interaction of digit presentation ear x nationality of subjects revealed a highly significant effect (F( 1,360) = 32.00,~ < .OOl). As shown in Fig. 2, the mean percentage of correct recognition in the right-ear presentation condition of British subject was 77.6%, and 66.4% in the left-ear digit presentation. This right-ear digit presentation advantage was statistically significant (t(208) = 4.82,~ < .OOl). On the other hand, the Japanese subjects’ right-ear digit presentation condition was 74.4%, and 71.3% in the left-ear digit presentation. Though the trend toward right-ear digit presentation advantage was apparent, the difference did not. reach a significant level (t(208) = 1.41). This strongly suggests that the asymmetric specialization of hemisphere function of the British in the task where spoken speech was presented dichotically with simultaneous environmental noise is more marked than that of the Japanese. These results apparently support the notion that linguistic differences have an effect upon the cerebral functioning in the pattern and degree of interhemispheric functional asymmetry as well as in the results of dichotic-listening studies with polyglots (Lhermitte et al., 1966; Bever, 1974)and also in tachistoscopic studies (Orbach, 1967; Walters & Zattore, 1978). Recently, we conducted an experiment (Hatta & Dimond, 1980)
‘60 f LEFT
RIGHT DIGIT
FIG. 2. Mean percentage function of digit presentation
of correct ear.
PRESENTATION
EAR
responses of Japanese and English subjects as a
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AND DIMOND
which attempted to compare the pattern and degree of cerebral asymmetries in visual-recognition tasks between Japanese and British students. Verbal and nonverbal visual materials were presented to the left or the right visual field using Japanese and British students as subjects. The results with verbal materials indicated the same direction of laterality and a similar degree of specialization in both groups of subject; however, the results with nonverbal materials demonstrated that British students showed a highly significant left-visual-field superiority while the Japanese showed nonsignificant asymmetry. From these results, we proposed more bilateral hemisphere functioning in the Japanese. This significant interaction of digit presentation ear x nationality of subjects is in accordance with this proposal because the performance in the left-ear digit presentation condition of Japanese subjects was significantly superior to that of the British (t(208) =2.14, p < .OS), while no such differences appeared in the right-ear digit presentation condition between both groups of subject (t(208) = 1.40). The superior performance under the left-ear digit presentation condition of the Japanese subjects must be referred to the fact that the right hemisphere of the Japanese may contribute more in the processing of spoken speech than that of the British. The Japanese language is more vowel dependent than English, because vowels form meaningful monosyllabic words such as /a/ (mute, quasi), /i/ (stomach, medicine), /u/ (cormorant), /e/ (picture, food, handle), /o/ (tail, cord). It is said that consonants are significantly perceived dominantly in the left hemisphere while the right hemispl.?re contributes more in the processing of vowels (Shankweiler & Studdert-Kennedy, 1967). The Japanese language therefore could well demand stronger language representation in the right hemisphere than does the English language. Processing the Japanese language requires a more integrated action of both hemispheres than does processing English, and this might influence the different degree of ear asymmetry as shown in these results. This interpretation is a tentative one and we have to seek more germane evidence. However, from this experiment, we suggest first that environmental sounds are processed predominantly in the right hemisphere for both Japanese and British, unlike the proposal of Tsunoda (1975, 1977), and second that there are differences in cerebral asymmetry of auditory function, especially in degree rather than in direction, between the Japanese and British, and this might be due to some linguistic differences. REFERENCES Bever, T. 1974. The relation of language development to cognitive development. In E. Lenneburg (Ed.), Language and the bruin. Jamaica Plain, MA: Neuroscience Research Progress Bulletin. Curry, F. K. W. 1967. A comparison of left-handed and right-handed subjects on a verbal and nonverbal dichotic listening task. Correx, 3, 343-342.
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Hatta, T., & Dimond, S. J. 1980.Comparison of lateral differences for digit and random form recognition in Japanese and Westerners. Journal of Experimental Psychology: Human perception
and performance,
6, 368-374.
Knox, D., & Kimura, D. 1970. Cerebral processing of nonverbal sounds in boys and girls. Neuropsychologia,
8, 227-237.
Lhermitte, R., Hicaen, H., Dubois, J., Cullioli, A., & Tabouret-Keller, A. 1966. Le probleme de l’aphasie des polyglottes: Remarques sur quelques observation. Neuropsychologia, 4, 315-329. Orbach, J. 1967.Differential recognition of Hebrew and English words in right and left visual 5, fields as a function of cerebral dominance and reading habits. Neuropsychologia, 127-134. Scott, S., Hynd, G. W., Hunt, L., & Weed, W. 1979. Cerebral speech lateralization in the native American Navajo. Neuropsychologia, 17, 89-92. Shankweiler, D., & Studdert-Kennedy, M. 1967. Identification of consonants and vowels presented to left and right ears. Quarterly Journal of Experimental Psychology, 19, 59-63. Tsunoda, T. 1975. Functional differences between right and left cerebral hemispheres detected by the key-tapping method. Brain and Language, 2, 152-170. Tsunoda, T. 1977. Brain and language. In Y. Tanaka, S. Omori, & N. Sawada (Eds.), Languuge, consciousness and life, pp. l-3 1. Tokyo: Kyoritsu-syuppan. Van Lanker, D., & Fromkin, V. A. 1973. Hemispheric specialization for pitch and “tone”: Evidence from Thai. Journal of Phonetics, I, 101-109. Walters, J., & Zatorre, R. J. 1978. Laterality differences for words identification in bilinguals. Brain and Language, 6, 158-167.