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Left-hemisphere language lateralization in bilinguals: Use of the concurrent activities paradigm
BRAIN
AND
LANGUAGE
23, 86-96 (1984)
Left-Hemisphere Language Lateralization in Bilinguals: Use of the Concurrent Activities Paradigm CARLOS SOARES Northeastern
University
Previous visual and auditory lateralization studies have demonstrated that the languages of bilinguals are laterahzed to the left hemisphere to the same extent as in monolingual controls (C. Soares & F. Grosjean, 1981, Perception and Psychophysics, 29, 599-604; C. Soares, 1982, Neuropsychologia, 20, 653-659). The present study tested the same group of Portuguese-English bilinguals and a group of English-speaking monolinguals on a series of concurrent activity, or time-sharing, tasks. Greater levels of disruption in finger tapping with the right hand than with the left hand occurred during the performance of those tasks which required overt speech production, and this for both bilinguals and monolinguals. As in the previous studies, there were no lateralization differences across the bilinguals’ two languages or between bilinguals and monolinguals. Thus, further evidence for equal levels of left-hemisphere dominance for language in bilinguals and monolinguals was provided by the use of the concurrent activities paradigm.
INTRODUCTION Evidence from a number of studies of hemispheric specialization in normal subjects and from reviews of case studies of brain-damaged patients has suggested that there may be a greater level of right-hemisphere participation in the language functions of bilinguals than that typically found in monolinguals [see Albert and Obler (1978), Galloway (1981, 1982), Vaid (1983), and Vaid and Genesee (1980) for reviews]. However, This research was part of the author’s doctoral dissertation. The author wishes to thank Linda Galloway, Francois Grosjean, Steve Harkins, Marcel Kinsboume, Harlan Lane, Joanne Miller, Harvey Sussman, Michael Terman, Joytsna Vaid, and Robert Zatorre for their comments on earlier drafts of this manuscript. Special thanks to Kerry Green for developing a computer program to analyze the data. Part of this research was supported by grants from The Department of Health and Human Services Biomedical Research Support (RR07143) and NIH (NS14923). Requests for reprints should be sent to Carlos Soares, Marketing Education, M.S.lD, Data General, 2400 Computer Drive, Westboro, MA 01581. 86 0093-934X/84 Copyright Au rights
$3.00
0 1984 by Academic Press, Inc. of reproduction in any form reserved.
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both of these sources of evidence are problematic. First, the case studies of bilingual aphasics often lack information regarding such critical factors as the site and extent of brain damage, the patient’s handedness, and pre- and postinjury levels of language proficiency (Galloway, 1981). It is also likely that the published studies constitute a biased sample of “unusual” cases (Galloway, 1981; Vaid & Genesee, 1980). Furthermore, a number of nonneurological factors, such as language fluency, frequency and recency of language usage, social and affective value of each of the languages, etc., may account for the differential effects of brain damage on the bilingual’s language during the aphasic stage as well as during the recovery process (Galloway, 1981; Kinsboume, 1982; Paradis, 1977). Second, the results of studies of hemispheric specialization for language in normal bilinguals have been mixed: Some show the typical left-hemisphere advantage, while others have found greater levels of right-hemisphere contribution to language processing in bilinguals than in monolinguals. One plausible explanation for this set of conflicting results may be that a number of factors have not been properly controlled for. As Obler, Zatorre, Galloway, and Vaid (1982) have pointed out, the sex and handedness of the subjects have often not been controlled. In addition, the bilinguals’ proficiency in their two languages has usually not been determined, and neither has a group of monolingual controls been included in order to provide a direct comparison of monolingual and bilingual performance. Soares and Grosjean (1981) and Soares (1982) controlled for these variables and obtained identical levels of left-hemisphere advantage in a group of bilinguals and monolingual control group across visual and auditory lateralization tasks. Thus converging evidence was provided for left-hemisphere dominance for language in bilinguals. Aside from tachistoscopic and auditory lateralization techniques for assessing hemispheric specialization for language, a third method has been used widely-the concurrent activities, or time-sharing, paradigm developed by Kinsbourne and Cook (1971). In a typical experiment using this technique, subjects are asked to read aloud or speak spontaneously while simultaneously finger tapping as fast as possible. The results show that, as compared to a baseline measure, there is a greater level of disruption in finger tapping when subjects attempt to read or speak aloud and concurrently tap with their right hand than when tapping with their left hand. These results are interpreted as providing evidence for the left hemisphere’s specialization for language since greater levels of interference occur when the concurrent activities are controlled by the left hemisphere (Kinsbourne & Hiscock, 1977). It should be noted that the language processing involved in the concurrent activities paradigm is linguistically more complex than that in tachistoscopic and auditory lateralization tasks. In the latter tasks, the processing only involves words, digits,
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letters, or nonsense syllables whereas in the concurrent activities paradigm at least sentence-level processing is involved. In the bilingual lateralization literature, there are two studies that used the concurrent activities paradigm and contradictory results were obtained. In the first study, Hynd, Teeter, and Stewart (1980) tested a group of Navajo-English bilinguals and found left-hemisphere dominance for both languages. Furthermore, they found that the level of left-right hemisphere asymmetry for the bilinguals in English (their second language, or L2) did not differ from the level obtained for a matched group of Englishspeaking monolinguals. For Navajo, the bilinguals’ first language (Ll), the level of left-hemisphere lateralization obtained was greater than that for L2, which might indicate that L2 receives greater input from the right hemisphere than LI. However, this difference in lateralization levels between Ll and L2 can most likely be explained by the fact that the bilinguals did not use Navajo on a regular basis and, therefore, had some difficulty performing the verbal tasks in that language. In the second study, Sussman, Franklin, and Simon (1982) used righthanded male bilinguals fluent in a number of different pairs of languages, one of which was always English, and a monolingual control group. Their results showed, first, that while both of the bilinguals’ languages were lateralized to the left hemisphere, they were significantly less lateralized than was English for the monolingual controls. Second, they found that the bilinguals’ L2 was less lateralized than their Ll. And, third, they divided the bilinguals into those who had acquired both languages before 6 years of age (early bilinguals) and those who had acquired one of their languages after that age (late bilinguals) and found that the early bilinguals had low but similar levels of left-hemisphere advantage for both of their languages. The late bilinguals, on the other hand, showed left-hemisphere advantage only for Ll; symmetrical hemispheric involvement was found for L2, demonstrating bilateral control over that language. Therefore, Sussman et al. propose that there is a greater level of righthemisphere contribution to language functions in bilinguals, especially for L2 when it is acquired late. The present study has two aims. The first aim is to determine language lateralization in bilinguals and monolinguals using the concurrent activities paradigm and, perhaps, extend our previous findings with visual and auditory techniques for assessing hemispheric specialization. As in our previous studies, the sex, handedness, and language fluency of the bilinguals was controlled, and a monolingual control group was included. In addition, natural language contexts were provided for the bilinguals’ verbal tasks. The second, and more minor, aim is to determine the processing level at which the interference between speaking and finger tapping occurs. To do this, silent reading and thinking were added as concurrent tasks to the usual tasks included in this paradigm: talking, reading aloud, and
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reciting automatisms (i.e., counting, saying the days of the week, or any other well-learned saying). If lateralized interference occurs in silent reading and thinking for which no speech output is required, then the observed interference probably occurs at a central level. However, if no lateralized interference is found for silent reading and thinking, then the interference between speech output and finger tapping is most likely due to overlap in motor programming during language production and finger tapping. METHOD Subjects. Thirty-two subjects participated in this study. Sixteen of the subjects were Portuguese-English male bilinguals whose first language was Portuguese and who first came into contact with English after 12 years of age (range 12-18). Their ages ranged from 20-35, with a mean of 24.2. The other 16 subjects were male English-speaking monolinguals (ages 20-24; mean of 21.3). All subjects were strong right-handers, as determined by a short questionnaire developed from Bryden (1977) and Oldfield (1971), with no left-handers in the immediate family. The bilinguals, who had all participated in the previous visual and auditory laterality studies (Soares & Grosjean, 1981; Soares, 1982), were selected for approximately equal and high fluency in Portuguese and English. Fluency was assessed by a questionnaire in which the subjects rated their fluency in reading, writing, speaking, and understanding Portuguese and English; a reading test in which subjects were timed while reading aloud passages of equal length in Portuguese and English; and a naming task in which subjects named objects found in various settings in 1 min. In order to participate in the study, the bilinguals had to rate their overall fluency in Portuguese and English equally, read the passages in approximately the same time (2 lo%), and name approximately the same number of objects (-r- 15%). In addition, care was taken to ensure that the bilinguals used both languages on a regular basis. All of the bilinguals moved to the United States in their adolescence and, therefore, learned English in school and through their interactions with English-speaking friends and in the community in general. The bilinguals reported using each of their languages about 50% of the time. Portuguese was used primarily in the home, with friends, and at Portuguese social events. English was used primarily at work and/or school. Procedure. Five tasks were used concurrently with finger tapping in order to assess hemispheric specialization for language. The bilinguals performed two sets of tasks, one in Portuguese and one in English. The monolinguals performed only one set, in English. Tusk I: T&ing-The monolinguals talked to the experimenter about the courses they were taking at the time, some school project they were working on, work performed at their jobs, or sporting events they had attended or watched on television. For the bilinguals, it was necessary to respect the domains of Portuguese and English language usage. Therefore, when speaking English to the experimenter (who was a Portuguese-English bilingual), they talked about topics for which English would be the natural language of communication, such as school activities or work situations. And, when speaking Portuguese to the experimenter, the bilinguals described events or activities which took place in the town where they had lived in Portugal. Tasks 2 and3: Reading Aloud and Silent Reading-Two different passages which had been translated from Portuguese into English were used in these two tasks. Subjects read different portions of one of the passages aloud or silently. The bilinguals read from one of the passages during the English set, and from the Portuguese version of the other passage for the Portuguese set. Across language sets, half of the bilinguals started with one passage, and half started with the other. The monolinguals read only the English versions of the passages. Half of the monolinguals read one passage, and half read the
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other passage. Task 4: Reciting Automatisms-Subjects were asked to name the days of the week, the months of the year, count from 1 to 20 and recite the alphabet. Since each of these tasks did not take 20 set to perform, they were repeated until 20 set had elapsed. The bilinguals recited each of the automatisms in Portuguese and in English in the appropriate language set. The monolinguals, as in the other tasks, recited only in English. Task 5: Thinking-In this task, the monolinguals were asked to think about what they were planning to do during the next weekend or on a vacation they were about to have. The bilinguals were asked to think in the appropriate language depending on the set. Again, as in the Talking Task, it was important to ensure that the respective domains of language usage were respected. Therefore, during the English set, the bilinguals were asked to think about their plans for the following weekend, or a vacation they were about to take in the United States. On the other hand, during the Portuguese set, they were asked to think about their plans for their next visit to Portugal. Subjects performed each of the tasks described above four times--twice while simultaneously finger tapping with the index and middle fingers of the right hand, and twice while simultaneously finger tapping with the corresponding fingers of the left hand. Each of the two task-hand combinations was performed for a 20-set trial. Finger tapping consisted of alternating taps with the index and middle fingers on two nonadjacent keys (spaced 3.5 cm apart) of a Visual 200 computer terminal (Visual Technology, Inc.) The order of hands and tasks was random for each subject, with the following restrictions: no more than three consecutive concurrent tasks were performed with the same hand and the same concurrent task was not performed consecutively with the same hand. In addition to the concurrent task trials, there were 10 control trials for each hand. Control trials consisted of finger tapping alone for 20 sec. The control trials were interspersed with the concurrent task trials according to the following rules: (1) when two or three concurrent tasks were performed consecutively with the same hand, control trials both preceded and followed the concurrent task trials; (2) when only one concurrent task trial was performed with one hand before switching to the other, a control trial either preceded or followed the concurrent task trial as determined by a coin flip. These limitations on a truly random order of trials and hand and the rules for inserting control trials were implemented in order to control for any effects due to fatigue. There was a 5- to IO-min rest period halfway through the session. Subjects were allowed 15-20 min to practice alternating finger tapping until they could perform adequately with each hand. Instructions were given to the subjects at the beginning as well as during the experiment to alternate finger taps as fast as possible in all trials. The bilinguals performed two sets of concurrent and control trials, one in Portuguese and one in English, each with a different random order. In one set all of the verbal materials and instructions were in English, and in the other the verbal materials and instructions were in Portuguese. Half of the bilinguals performed the English set first, and half performed the Portuguese set first. There was a 45-min rest period between language sets, during which the bilinguals participated in an unrelated experiment. The monolingual controls performed only one set of concurrent task and control trials in English. Key taps were tabulated directly by a PDP-11 computer.
RESULTS AND DISCUSSION The percentage change in finger tapping for each hand during each concurrent task was computed for each subject using the formula (from Kinsboume and Hiscock, 1977) % Change = c--v c
x 100
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where c is the average number of finger taps on the control trials, and v is the average number of finger taps in the concurrent task. The resulting values were analyzed in two analyses of variance. One compared the performance of the bilinguals in the English set with the monolinguals, and the other compared the performance of the bilinguals in the English and the Portuguese sets. Monolinguals
vs. Bilinguals-English
The mean percentage reduction in finger tapping for the right and for the left hand for each group and for each concurrent task within each group is shown in Fig. 1. Several observations can be made based on this figure. First, there is a greater overall reduction in finger tapping for the right hand when compared to the left hand, indicating that more interference was found in the left hemisphere during the performance of the concurrent tasks. This result is typically obtained in experiments using this paradigm (Kinsbourne & Hiscock, 1977). Second, the overall performance of the bilinguals and monolinguals was very similar, as had been found in our previous studies of visual and auditory laterality tasks MONOLINGUALS-
q q
ENGLISH I
Talking
Reciting Automatlams
BILI
Talking
Reciting A”tomatlsms
Reading Aloud
NGUALS
Reading Aloud
SII*nt Reading
-
x
Thinking
Group Meall
Thlnklng
Grwp Meall
x
Right Left
Hand Hand
Slgnllicant IP~.O11
ENGLISH
SlIerIt Read Ing
FIG. 1. Percentage reduction in finger tapping for right and left hand for each group (averaged across tasks) and for each of the concurrent tasks. Monolinguals are shown at the top, and Bilinguals in the English set are shown at the bottom of the figure. Significant right-hand/left-hand differences in finger tapping reduction are indicated by asterisks (p < .Ol).
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(Soares & Grosjean, 1981; Soares, 1982). Third, the degree of reduction in finger tapping and in asymmetrical interference varied with the task. Talking, Reading Aloud, Silent Reading, and Reciting Automatisms showed greater overall reduction than Thinking. And, both Silent Reading and Thinking demonstrated less lateralized interference than the other concurrent tasks. A Group(2) x Hands(2) x Tasks(S) analysis of variance confirmed these observations. Of the main effects, Hand and Task were significant while Group was not. The Hand main effect [F(l, 30) = 29.60, p < .OOl] shows that there was significantly more reduction in finger tapping with the right hand (8.68%) than with the leit hand (4.69%) during concurrent tasks. This result is interpreted as suggesting a greater level of lefthemisphere interference overall as is typically reported in studies using this laterality paradigm (Kinsbourne & Hiscock, 1977). Of the results critical to the bilingualism issue, neither the Group main effect nor any of its interactions reached significance. This demonstrates that overall performance and laterality levels were similar for the bilinguals in the English set and for the monolinguals, in agreement with the results of our previous visual and auditory lateralization studies. A second aim of this study was to determine the processing level at which the interference occurs in the performance of the concurrent tasks. In answering this question, it should be noted first that the Task main effect was signiticant [F(l, 120) = 4.64, p < .Ol]. A Neuman-Keuls test showed that overall finger tapping during Thinking (3.88%) was significantly less reduced than during the performance of the other concurrent tasks (p < .05; Talking = 7.72%; Reading Aloud = 7.08%; Silent Reading = 6.23%; Reciting Automatisms = 8.52%). Second, the Hand x Task interaction was also significant [F(4, 120) = 3.27, p < .05]. A NeumanKeuls test showed that while there was significantly more disruption of finger tapping with the right hand than with the left hand during Talking, Reading Aloud, and Reciting Automatisms, those differences were not significant for Silent Reading and Thinking (p < .05). A series of planned contrasts on the Group x Hand x Task interaction revealed that this pattern of results was true for both bilinguals and monolinguals,’ again demonstrating the similarity of lateralized performance for these two groups of subjects. Since greater levels of right-hand vs. left-hand disruption were found for Talking, Reading Aloud, and Reciting Automatisms, left’ For the monolinguals: Talking [F(l, 120) = 8.03, p < ,011; Reading Aloud [F(l, 120) = 10.55, p < ,011; Silent Reading [F(l, 120) = 1.86, n.s.1; Thinking [F(l, 120) = 0.32, n.s.1; and Reciting Automatisms [F(l, 120) = 10.33, p < .Ol]. For the Bilinguals in the English set: Talking [F(l, 120) = 9.70, p < .Ol]; Reading Aloud [F(l, 120) = 11.70, p < .Ol]; Silent Reading [F(l, 120) = 1.77, n.s.1; Thinking [F(l, 120) = 0.44, n.s.1; and Reciting Automatisms [F(l, 120) = 8.42, p < .Ol].
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hemisphere control over speech production is clearly demonstrated. This implies that the interference between finger tapping and speech production is due to overlap either at the planning or the execution level of the movements required for the production of speech and finger tapping, rather than at a more central or cognitive level. These results are predicted by the “cerebral space” model proposed by Kinsbourne and Hicks (1978) to account for such intertask interferences. We should be cautious in the interpretation of these results, however, as there is no independent evidence that the subjects were actually following the experimenter’s instructions in the Silent Reading and Thinking tasks. Bilinguals-English
and Portuguese
The mean percentage reduction in finger tapping for the right and for the left hand for each language and for each of the concurrent tasks within each language is shown in Fig. 2. As can be seen, these results parallel those shown in Fig. 1 in which the performance of the monolinguals and the bilinguals in English was compared. First, there was a greater reduction in right-hand finger tapping than left-hand finger tapping during the performance of the concurrent tasks. Second, the levels of lateralization across languages are very similar. Third, the degree of reduction in finger tapping as well as the lateralized performance varied across tasks. A Languages(2) x Hands(2) x Tasks(S) analysis of variance confirmed these observations. As in the previous analysis of variance, two main effects were significant: Hand and Task, while Language was not. The Hand main effect [F(l, IS)= 33.24, p < .OOl] indicates that there was significantly more reduction in finger tapping with the right hand (8.24%) than with the left hand (3.46%) during the performance of the concurrent tasks. Again, this result is interpreted as providing evidence for greater involvement of the left hemisphere in the tasks used in this laterality paradigm (Kinsbourne & Hiscock, 1977). The Task main effect [F(4, 60) = 4.28, p < .Ol] was analyzed with the Neuman-Keuls test. This analysis showed that the overall reduction in finger tapping for Silent Reading (3.69%) and Thinking (4.17%) was significantly lower (p < .05) than that for Talking (6.73%), Reading Aloud (6.11%), and Reciting Automatisms (8.55%). Neither the Language main effect nor any of its interactions reached significance demonstrating that the bilinguals’ two languages are left-lateralized to the same extent. This finding of similar left-hemisphere lateralization levels for the bilinguals’ Ll and L2 is consistent with the results previously obtained in the visual (Soares & Grosjean, 1981) and auditory (Soares, 1982) laterality studies with the same group of bilingual subjects. In addition, planned comparisons of right-hand/left-hand reductions in finger tapping for each of the tasks in the Portuguese set revealed a pattern of results similar to those obtained for the monolinguals
94
CARLOS SOARES EILINGUALS
-
ENGLISH Ll
14
Right
Hand
12 X
10
Signiticant IPc.Oll
6 6 4 2 0 Talking
Recltlng Automatlsms
BILI 12-
NGUALS
-
Thinking
Group Mean
PORTUGUESE
x
I
P
lo8-
x
x
Silent Readlng
Reading Aloud
x
I
-
I
i, i
s4-
00 -2-
Talking
Reciting Automatisma
Reading Aloud
Silent Readlng
Thinking
G ro”p Mean
FIG. 2. Percentage reduction in finger tapping for right and left hand for bilinguals (averaged across tasks) and for each of the concurrent tasks. Bilinguals in the English set are shown at the top, and in the Portuguese set are shown at the bottom of the figure. Significant right-hand/left-hand differences in finger tapping reduction are indicated by asterisks (p < .Ol).
and the bilinguals in the English set.* That is, significant right-hand/lefthand disruption differences were found for Talking, Reading Aloud, and Reciting Automatisms, but not for Silent Reading and Thinking. An analysis of lateralization for individual subjects further demonstrates the similarity of monolingual and bilingual performance in this experimental paradigm. The number of subjects in each group with left-hemisphere dominance (Ll in monolinguals; Ll and L2 in bilinguals) was compared with the number of subjects with other dominance patterns. Since some of the cells contained a small number of subjects, the Fisher Exact Probability Test (Bradley, 1968; Siegel, 1956) was used and the results showed that the individual laterality patterns for the two groups were not statistically different (E, = .26). Our previous visual and auditory laterality studies yielded similar results. * For the Bilinguals in the Portuguese set: Talking [F(l, 60) = 14.27, p < .Ol]; Reading Aloud [F(l, 60) = 14.01, p < .Ol]; Silent Reading [F(l, 60) = 2.10, n.s.1; Thinking [F(l, 60) = 1.75, n.s.1; and Reciting Automatisms [F(l, 60) = 12.16, p < ,011.
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GENERAL DISCUSSION Two main points can be made regarding language lateralization in bilinguals. The first is that bilinguals, as a group, do not differ from monolingual controls in terms of overall level of left-hemisphere dominance for language. The second point is that the bilinguals’ Ll (Portuguese) and L2 (English) do not differ in terms of overall left-hemisphere lateralization even though this group of bilinguals learned L2 in their adolescence, and hence are late bilinguals. These results together with those of our previous visual and auditory laterality tasks provide strong evidence for similar levels of left-hemisphere dominance for language in bilinguals and monolinguals . These findings are in agreement with those reported by Hynd et al., (1980) in that similar levels of left-hemisphere lateralization for the bilinguals’ L2 and monolinguals were found. On the other hand, the present results are quite different from those obtained by Sussman et al. (1982), who found that bilinguals showed weaker levels of left-hemisphere lateralization than monolinguals for both Ll and L2. In addition, while early bilinguals in their study demonstrated similar levels of weak lefthemisphere advantage for Ll and L2, late bilinguals showed left-hemisphere advantage for Ll, but bilateral control for L2. There are a number of differences between the present study and that of Sussman et al. which may well account for the contradictory results. First, the experimenters in Sussman et al. did not always speak the bilinguals’ language other than English and hence when the bilinguals performed verbal tasks they did so in an unnatural sociolinguistic context. In the present study, the experimenter spoke both the bilinguals’ languages and the topics chosen were appropriate to those languages. Second, in Sussman et al. half of the bilinguals were over 30 years old, and over 20% were 40 years old. The monolingual control group did not cover this same age range. In the present study, the bilinguals and monolinguals were matched for age. And, third, in Sussman et al., some 70% of the late bilinguals were American-born English speakers who learned their second language in an English-speaking environment. In contrast, the bilinguals in the present study learned each of their languages in their respective natural environments. In summary, the present study using the concurrent activities paradigm and our previous experiments using visual and auditory language laterality tasks provide converging evidence for a level of left-hemisphere language processing in bilinguals that is the same as in monolinguals. Recent studies using the dichotic listening technique (Galloway, 1981; Gordon, 1980; Gordon 8z Zatorre, 1981) extend the present findings to include adult bilinguals of varying degrees of fluency, varying degrees of second language usage, and to bilingual children. All of these studies show that
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left-hemisphere lateralization for language is the prevalent pattern in bilinguals as it is in monolinguals. REFERENCES Albert, M. L., & Obler, L. K. 1978. The bilingual brain. New York: Academic Press. Bradley, J. V. 1968. Distribution-free stutisrical tests. Englewood Cliffs, NJ: PrenticeHall. Pp. 199-201. Bryden, M. P. 1977. Measuring handedness with questionnaires. Neuropyschologia, 15, 617-624. Galloway, L. 1981. Contributions of the right cerebral hemisphere to language and communication: Issues on cerebral dominance with special emphasis on bilingualism, second language acquisition, sex differences, and certain ethnic groups. Doctoral dissertation, Department of Linguistics, University of California, Los Angeles. Galloway, L. 1982. The convolutions of second language learning: Towards a neuropsychological model of bilingualism and second language performance, a theoretical article with a critical review of current research and some new hypotheses. Language Learning, 31, 439-464.
Gordon, H. W. 1980. Cerebral organization in bilinguals. I. Lateralization. Bruin and Language, 9, 255-268. Gordon, D. P., & Zatorre, R. J. 1981. A right-ear advantage for dichotic listening in bilingual children. Brain and Language, 13, 389-396. Hynd, G. W., Teeter, A., & Stewart, J. 1980. Acculturation and the lateralization of speech in the bilingual Native American. International Journal of Neuroscience, 11, l-7. Kinsboume, M. 1982. Neuropsychological aspects of bilingualism. In H. Winitz (Ed.), Native language and foreign language acquisition. Annals of the New York Academy of Sciences,
379,
50-58.
Kinsboume, M., & Cook, J. 1971. Generalized and lateralized effects of concurrent verbalization on a unimanual skill. Quarterly Journal of Experimental Psychology, 23, 341-345. Kinsboume, M., & Hicks, R. F. 1978. Functional cerebral space: A model for overflow, transfer, and interference effects in human performance. In J. Requin (Ed.), Attention and performance, VIZ. Hillsdale, NJ: Erlbaum. Pp. 345-362. Kinsboume, M., & Hiscock, M. 1977. Does cerebral dominance develop? In S. J. Segalowitz & F. A. Gruber (Eds.), Language development and neurological theory. New York: Academic Press. Pp. 171-191. Obler, L., Zatorre, R., Galloway, L., & Vaid, J. 1982. Cerebral lateralization in bilinguals: Methodological issues. Brain and Language, 15, 40-54. Oldfield, R. C. 1971. The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, 97-113. Paradis, M. Bilingualism and aphasia. 1977. In H. Whitaker & H. A. Whitaker (Eds.), Studies in neurolinguistics, New York: Academic Press. Vol. 3, pp. 65-121. Siegel, S. 1956. Nonparametric statistics. New York: McGraw-Hill. Pp. 96-101. Soares, C. 1982.Converging evidence for left hemisphere language lateralization in bilinguals. Neuropsychologia, 20, 653-659. Soares, C., & Grosjean, F. 1981. Left hemisphere language lateralization in bilinguals and monolinguals. Perception and Psychophysics, 29, 599404. Sussman, H. M., Franklin, P., & Simon, T. 1982. Bilingual speech: Bilateral control? Bruin and Language, 15, 125-142. Vaid, J. 1983. Bilingualism and brain lateralization. In S. J. Segalowitz (Ed.), Language functions and brain organization. New York: Academic Press. Vaid, J., & Genesee, F. 1980. Neuropsychological approaches to bilingualism: A critical review. Canadian Journal of Psychology, 34, 419-447.
AND
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Left-Hemisphere Language Lateralization in Bilinguals: Use of the Concurrent Activities Paradigm CARLOS SOARES Northeastern
University
Previous visual and auditory lateralization studies have demonstrated that the languages of bilinguals are laterahzed to the left hemisphere to the same extent as in monolingual controls (C. Soares & F. Grosjean, 1981, Perception and Psychophysics, 29, 599-604; C. Soares, 1982, Neuropsychologia, 20, 653-659). The present study tested the same group of Portuguese-English bilinguals and a group of English-speaking monolinguals on a series of concurrent activity, or time-sharing, tasks. Greater levels of disruption in finger tapping with the right hand than with the left hand occurred during the performance of those tasks which required overt speech production, and this for both bilinguals and monolinguals. As in the previous studies, there were no lateralization differences across the bilinguals’ two languages or between bilinguals and monolinguals. Thus, further evidence for equal levels of left-hemisphere dominance for language in bilinguals and monolinguals was provided by the use of the concurrent activities paradigm.
INTRODUCTION Evidence from a number of studies of hemispheric specialization in normal subjects and from reviews of case studies of brain-damaged patients has suggested that there may be a greater level of right-hemisphere participation in the language functions of bilinguals than that typically found in monolinguals [see Albert and Obler (1978), Galloway (1981, 1982), Vaid (1983), and Vaid and Genesee (1980) for reviews]. However, This research was part of the author’s doctoral dissertation. The author wishes to thank Linda Galloway, Francois Grosjean, Steve Harkins, Marcel Kinsboume, Harlan Lane, Joanne Miller, Harvey Sussman, Michael Terman, Joytsna Vaid, and Robert Zatorre for their comments on earlier drafts of this manuscript. Special thanks to Kerry Green for developing a computer program to analyze the data. Part of this research was supported by grants from The Department of Health and Human Services Biomedical Research Support (RR07143) and NIH (NS14923). Requests for reprints should be sent to Carlos Soares, Marketing Education, M.S.lD, Data General, 2400 Computer Drive, Westboro, MA 01581. 86 0093-934X/84 Copyright Au rights
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0 1984 by Academic Press, Inc. of reproduction in any form reserved.
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both of these sources of evidence are problematic. First, the case studies of bilingual aphasics often lack information regarding such critical factors as the site and extent of brain damage, the patient’s handedness, and pre- and postinjury levels of language proficiency (Galloway, 1981). It is also likely that the published studies constitute a biased sample of “unusual” cases (Galloway, 1981; Vaid & Genesee, 1980). Furthermore, a number of nonneurological factors, such as language fluency, frequency and recency of language usage, social and affective value of each of the languages, etc., may account for the differential effects of brain damage on the bilingual’s language during the aphasic stage as well as during the recovery process (Galloway, 1981; Kinsboume, 1982; Paradis, 1977). Second, the results of studies of hemispheric specialization for language in normal bilinguals have been mixed: Some show the typical left-hemisphere advantage, while others have found greater levels of right-hemisphere contribution to language processing in bilinguals than in monolinguals. One plausible explanation for this set of conflicting results may be that a number of factors have not been properly controlled for. As Obler, Zatorre, Galloway, and Vaid (1982) have pointed out, the sex and handedness of the subjects have often not been controlled. In addition, the bilinguals’ proficiency in their two languages has usually not been determined, and neither has a group of monolingual controls been included in order to provide a direct comparison of monolingual and bilingual performance. Soares and Grosjean (1981) and Soares (1982) controlled for these variables and obtained identical levels of left-hemisphere advantage in a group of bilinguals and monolingual control group across visual and auditory lateralization tasks. Thus converging evidence was provided for left-hemisphere dominance for language in bilinguals. Aside from tachistoscopic and auditory lateralization techniques for assessing hemispheric specialization for language, a third method has been used widely-the concurrent activities, or time-sharing, paradigm developed by Kinsbourne and Cook (1971). In a typical experiment using this technique, subjects are asked to read aloud or speak spontaneously while simultaneously finger tapping as fast as possible. The results show that, as compared to a baseline measure, there is a greater level of disruption in finger tapping when subjects attempt to read or speak aloud and concurrently tap with their right hand than when tapping with their left hand. These results are interpreted as providing evidence for the left hemisphere’s specialization for language since greater levels of interference occur when the concurrent activities are controlled by the left hemisphere (Kinsbourne & Hiscock, 1977). It should be noted that the language processing involved in the concurrent activities paradigm is linguistically more complex than that in tachistoscopic and auditory lateralization tasks. In the latter tasks, the processing only involves words, digits,
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letters, or nonsense syllables whereas in the concurrent activities paradigm at least sentence-level processing is involved. In the bilingual lateralization literature, there are two studies that used the concurrent activities paradigm and contradictory results were obtained. In the first study, Hynd, Teeter, and Stewart (1980) tested a group of Navajo-English bilinguals and found left-hemisphere dominance for both languages. Furthermore, they found that the level of left-right hemisphere asymmetry for the bilinguals in English (their second language, or L2) did not differ from the level obtained for a matched group of Englishspeaking monolinguals. For Navajo, the bilinguals’ first language (Ll), the level of left-hemisphere lateralization obtained was greater than that for L2, which might indicate that L2 receives greater input from the right hemisphere than LI. However, this difference in lateralization levels between Ll and L2 can most likely be explained by the fact that the bilinguals did not use Navajo on a regular basis and, therefore, had some difficulty performing the verbal tasks in that language. In the second study, Sussman, Franklin, and Simon (1982) used righthanded male bilinguals fluent in a number of different pairs of languages, one of which was always English, and a monolingual control group. Their results showed, first, that while both of the bilinguals’ languages were lateralized to the left hemisphere, they were significantly less lateralized than was English for the monolingual controls. Second, they found that the bilinguals’ L2 was less lateralized than their Ll. And, third, they divided the bilinguals into those who had acquired both languages before 6 years of age (early bilinguals) and those who had acquired one of their languages after that age (late bilinguals) and found that the early bilinguals had low but similar levels of left-hemisphere advantage for both of their languages. The late bilinguals, on the other hand, showed left-hemisphere advantage only for Ll; symmetrical hemispheric involvement was found for L2, demonstrating bilateral control over that language. Therefore, Sussman et al. propose that there is a greater level of righthemisphere contribution to language functions in bilinguals, especially for L2 when it is acquired late. The present study has two aims. The first aim is to determine language lateralization in bilinguals and monolinguals using the concurrent activities paradigm and, perhaps, extend our previous findings with visual and auditory techniques for assessing hemispheric specialization. As in our previous studies, the sex, handedness, and language fluency of the bilinguals was controlled, and a monolingual control group was included. In addition, natural language contexts were provided for the bilinguals’ verbal tasks. The second, and more minor, aim is to determine the processing level at which the interference between speaking and finger tapping occurs. To do this, silent reading and thinking were added as concurrent tasks to the usual tasks included in this paradigm: talking, reading aloud, and
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reciting automatisms (i.e., counting, saying the days of the week, or any other well-learned saying). If lateralized interference occurs in silent reading and thinking for which no speech output is required, then the observed interference probably occurs at a central level. However, if no lateralized interference is found for silent reading and thinking, then the interference between speech output and finger tapping is most likely due to overlap in motor programming during language production and finger tapping. METHOD Subjects. Thirty-two subjects participated in this study. Sixteen of the subjects were Portuguese-English male bilinguals whose first language was Portuguese and who first came into contact with English after 12 years of age (range 12-18). Their ages ranged from 20-35, with a mean of 24.2. The other 16 subjects were male English-speaking monolinguals (ages 20-24; mean of 21.3). All subjects were strong right-handers, as determined by a short questionnaire developed from Bryden (1977) and Oldfield (1971), with no left-handers in the immediate family. The bilinguals, who had all participated in the previous visual and auditory laterality studies (Soares & Grosjean, 1981; Soares, 1982), were selected for approximately equal and high fluency in Portuguese and English. Fluency was assessed by a questionnaire in which the subjects rated their fluency in reading, writing, speaking, and understanding Portuguese and English; a reading test in which subjects were timed while reading aloud passages of equal length in Portuguese and English; and a naming task in which subjects named objects found in various settings in 1 min. In order to participate in the study, the bilinguals had to rate their overall fluency in Portuguese and English equally, read the passages in approximately the same time (2 lo%), and name approximately the same number of objects (-r- 15%). In addition, care was taken to ensure that the bilinguals used both languages on a regular basis. All of the bilinguals moved to the United States in their adolescence and, therefore, learned English in school and through their interactions with English-speaking friends and in the community in general. The bilinguals reported using each of their languages about 50% of the time. Portuguese was used primarily in the home, with friends, and at Portuguese social events. English was used primarily at work and/or school. Procedure. Five tasks were used concurrently with finger tapping in order to assess hemispheric specialization for language. The bilinguals performed two sets of tasks, one in Portuguese and one in English. The monolinguals performed only one set, in English. Tusk I: T&ing-The monolinguals talked to the experimenter about the courses they were taking at the time, some school project they were working on, work performed at their jobs, or sporting events they had attended or watched on television. For the bilinguals, it was necessary to respect the domains of Portuguese and English language usage. Therefore, when speaking English to the experimenter (who was a Portuguese-English bilingual), they talked about topics for which English would be the natural language of communication, such as school activities or work situations. And, when speaking Portuguese to the experimenter, the bilinguals described events or activities which took place in the town where they had lived in Portugal. Tasks 2 and3: Reading Aloud and Silent Reading-Two different passages which had been translated from Portuguese into English were used in these two tasks. Subjects read different portions of one of the passages aloud or silently. The bilinguals read from one of the passages during the English set, and from the Portuguese version of the other passage for the Portuguese set. Across language sets, half of the bilinguals started with one passage, and half started with the other. The monolinguals read only the English versions of the passages. Half of the monolinguals read one passage, and half read the
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other passage. Task 4: Reciting Automatisms-Subjects were asked to name the days of the week, the months of the year, count from 1 to 20 and recite the alphabet. Since each of these tasks did not take 20 set to perform, they were repeated until 20 set had elapsed. The bilinguals recited each of the automatisms in Portuguese and in English in the appropriate language set. The monolinguals, as in the other tasks, recited only in English. Task 5: Thinking-In this task, the monolinguals were asked to think about what they were planning to do during the next weekend or on a vacation they were about to have. The bilinguals were asked to think in the appropriate language depending on the set. Again, as in the Talking Task, it was important to ensure that the respective domains of language usage were respected. Therefore, during the English set, the bilinguals were asked to think about their plans for the following weekend, or a vacation they were about to take in the United States. On the other hand, during the Portuguese set, they were asked to think about their plans for their next visit to Portugal. Subjects performed each of the tasks described above four times--twice while simultaneously finger tapping with the index and middle fingers of the right hand, and twice while simultaneously finger tapping with the corresponding fingers of the left hand. Each of the two task-hand combinations was performed for a 20-set trial. Finger tapping consisted of alternating taps with the index and middle fingers on two nonadjacent keys (spaced 3.5 cm apart) of a Visual 200 computer terminal (Visual Technology, Inc.) The order of hands and tasks was random for each subject, with the following restrictions: no more than three consecutive concurrent tasks were performed with the same hand and the same concurrent task was not performed consecutively with the same hand. In addition to the concurrent task trials, there were 10 control trials for each hand. Control trials consisted of finger tapping alone for 20 sec. The control trials were interspersed with the concurrent task trials according to the following rules: (1) when two or three concurrent tasks were performed consecutively with the same hand, control trials both preceded and followed the concurrent task trials; (2) when only one concurrent task trial was performed with one hand before switching to the other, a control trial either preceded or followed the concurrent task trial as determined by a coin flip. These limitations on a truly random order of trials and hand and the rules for inserting control trials were implemented in order to control for any effects due to fatigue. There was a 5- to IO-min rest period halfway through the session. Subjects were allowed 15-20 min to practice alternating finger tapping until they could perform adequately with each hand. Instructions were given to the subjects at the beginning as well as during the experiment to alternate finger taps as fast as possible in all trials. The bilinguals performed two sets of concurrent and control trials, one in Portuguese and one in English, each with a different random order. In one set all of the verbal materials and instructions were in English, and in the other the verbal materials and instructions were in Portuguese. Half of the bilinguals performed the English set first, and half performed the Portuguese set first. There was a 45-min rest period between language sets, during which the bilinguals participated in an unrelated experiment. The monolingual controls performed only one set of concurrent task and control trials in English. Key taps were tabulated directly by a PDP-11 computer.
RESULTS AND DISCUSSION The percentage change in finger tapping for each hand during each concurrent task was computed for each subject using the formula (from Kinsboume and Hiscock, 1977) % Change = c--v c
x 100
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where c is the average number of finger taps on the control trials, and v is the average number of finger taps in the concurrent task. The resulting values were analyzed in two analyses of variance. One compared the performance of the bilinguals in the English set with the monolinguals, and the other compared the performance of the bilinguals in the English and the Portuguese sets. Monolinguals
vs. Bilinguals-English
The mean percentage reduction in finger tapping for the right and for the left hand for each group and for each concurrent task within each group is shown in Fig. 1. Several observations can be made based on this figure. First, there is a greater overall reduction in finger tapping for the right hand when compared to the left hand, indicating that more interference was found in the left hemisphere during the performance of the concurrent tasks. This result is typically obtained in experiments using this paradigm (Kinsbourne & Hiscock, 1977). Second, the overall performance of the bilinguals and monolinguals was very similar, as had been found in our previous studies of visual and auditory laterality tasks MONOLINGUALS-
q q
ENGLISH I
Talking
Reciting Automatlams
BILI
Talking
Reciting A”tomatlsms
Reading Aloud
NGUALS
Reading Aloud
SII*nt Reading
-
x
Thinking
Group Meall
Thlnklng
Grwp Meall
x
Right Left
Hand Hand
Slgnllicant IP~.O11
ENGLISH
SlIerIt Read Ing
FIG. 1. Percentage reduction in finger tapping for right and left hand for each group (averaged across tasks) and for each of the concurrent tasks. Monolinguals are shown at the top, and Bilinguals in the English set are shown at the bottom of the figure. Significant right-hand/left-hand differences in finger tapping reduction are indicated by asterisks (p < .Ol).
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(Soares & Grosjean, 1981; Soares, 1982). Third, the degree of reduction in finger tapping and in asymmetrical interference varied with the task. Talking, Reading Aloud, Silent Reading, and Reciting Automatisms showed greater overall reduction than Thinking. And, both Silent Reading and Thinking demonstrated less lateralized interference than the other concurrent tasks. A Group(2) x Hands(2) x Tasks(S) analysis of variance confirmed these observations. Of the main effects, Hand and Task were significant while Group was not. The Hand main effect [F(l, 30) = 29.60, p < .OOl] shows that there was significantly more reduction in finger tapping with the right hand (8.68%) than with the leit hand (4.69%) during concurrent tasks. This result is interpreted as suggesting a greater level of lefthemisphere interference overall as is typically reported in studies using this laterality paradigm (Kinsbourne & Hiscock, 1977). Of the results critical to the bilingualism issue, neither the Group main effect nor any of its interactions reached significance. This demonstrates that overall performance and laterality levels were similar for the bilinguals in the English set and for the monolinguals, in agreement with the results of our previous visual and auditory lateralization studies. A second aim of this study was to determine the processing level at which the interference occurs in the performance of the concurrent tasks. In answering this question, it should be noted first that the Task main effect was signiticant [F(l, 120) = 4.64, p < .Ol]. A Neuman-Keuls test showed that overall finger tapping during Thinking (3.88%) was significantly less reduced than during the performance of the other concurrent tasks (p < .05; Talking = 7.72%; Reading Aloud = 7.08%; Silent Reading = 6.23%; Reciting Automatisms = 8.52%). Second, the Hand x Task interaction was also significant [F(4, 120) = 3.27, p < .05]. A NeumanKeuls test showed that while there was significantly more disruption of finger tapping with the right hand than with the left hand during Talking, Reading Aloud, and Reciting Automatisms, those differences were not significant for Silent Reading and Thinking (p < .05). A series of planned contrasts on the Group x Hand x Task interaction revealed that this pattern of results was true for both bilinguals and monolinguals,’ again demonstrating the similarity of lateralized performance for these two groups of subjects. Since greater levels of right-hand vs. left-hand disruption were found for Talking, Reading Aloud, and Reciting Automatisms, left’ For the monolinguals: Talking [F(l, 120) = 8.03, p < ,011; Reading Aloud [F(l, 120) = 10.55, p < ,011; Silent Reading [F(l, 120) = 1.86, n.s.1; Thinking [F(l, 120) = 0.32, n.s.1; and Reciting Automatisms [F(l, 120) = 10.33, p < .Ol]. For the Bilinguals in the English set: Talking [F(l, 120) = 9.70, p < .Ol]; Reading Aloud [F(l, 120) = 11.70, p < .Ol]; Silent Reading [F(l, 120) = 1.77, n.s.1; Thinking [F(l, 120) = 0.44, n.s.1; and Reciting Automatisms [F(l, 120) = 8.42, p < .Ol].
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hemisphere control over speech production is clearly demonstrated. This implies that the interference between finger tapping and speech production is due to overlap either at the planning or the execution level of the movements required for the production of speech and finger tapping, rather than at a more central or cognitive level. These results are predicted by the “cerebral space” model proposed by Kinsbourne and Hicks (1978) to account for such intertask interferences. We should be cautious in the interpretation of these results, however, as there is no independent evidence that the subjects were actually following the experimenter’s instructions in the Silent Reading and Thinking tasks. Bilinguals-English
and Portuguese
The mean percentage reduction in finger tapping for the right and for the left hand for each language and for each of the concurrent tasks within each language is shown in Fig. 2. As can be seen, these results parallel those shown in Fig. 1 in which the performance of the monolinguals and the bilinguals in English was compared. First, there was a greater reduction in right-hand finger tapping than left-hand finger tapping during the performance of the concurrent tasks. Second, the levels of lateralization across languages are very similar. Third, the degree of reduction in finger tapping as well as the lateralized performance varied across tasks. A Languages(2) x Hands(2) x Tasks(S) analysis of variance confirmed these observations. As in the previous analysis of variance, two main effects were significant: Hand and Task, while Language was not. The Hand main effect [F(l, IS)= 33.24, p < .OOl] indicates that there was significantly more reduction in finger tapping with the right hand (8.24%) than with the left hand (3.46%) during the performance of the concurrent tasks. Again, this result is interpreted as providing evidence for greater involvement of the left hemisphere in the tasks used in this laterality paradigm (Kinsbourne & Hiscock, 1977). The Task main effect [F(4, 60) = 4.28, p < .Ol] was analyzed with the Neuman-Keuls test. This analysis showed that the overall reduction in finger tapping for Silent Reading (3.69%) and Thinking (4.17%) was significantly lower (p < .05) than that for Talking (6.73%), Reading Aloud (6.11%), and Reciting Automatisms (8.55%). Neither the Language main effect nor any of its interactions reached significance demonstrating that the bilinguals’ two languages are left-lateralized to the same extent. This finding of similar left-hemisphere lateralization levels for the bilinguals’ Ll and L2 is consistent with the results previously obtained in the visual (Soares & Grosjean, 1981) and auditory (Soares, 1982) laterality studies with the same group of bilingual subjects. In addition, planned comparisons of right-hand/left-hand reductions in finger tapping for each of the tasks in the Portuguese set revealed a pattern of results similar to those obtained for the monolinguals
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-
ENGLISH Ll
14
Right
Hand
12 X
10
Signiticant IPc.Oll
6 6 4 2 0 Talking
Recltlng Automatlsms
BILI 12-
NGUALS
-
Thinking
Group Mean
PORTUGUESE
x
I
P
lo8-
x
x
Silent Readlng
Reading Aloud
x
I
-
I
i, i
s4-
00 -2-
Talking
Reciting Automatisma
Reading Aloud
Silent Readlng
Thinking
G ro”p Mean
FIG. 2. Percentage reduction in finger tapping for right and left hand for bilinguals (averaged across tasks) and for each of the concurrent tasks. Bilinguals in the English set are shown at the top, and in the Portuguese set are shown at the bottom of the figure. Significant right-hand/left-hand differences in finger tapping reduction are indicated by asterisks (p < .Ol).
and the bilinguals in the English set.* That is, significant right-hand/lefthand disruption differences were found for Talking, Reading Aloud, and Reciting Automatisms, but not for Silent Reading and Thinking. An analysis of lateralization for individual subjects further demonstrates the similarity of monolingual and bilingual performance in this experimental paradigm. The number of subjects in each group with left-hemisphere dominance (Ll in monolinguals; Ll and L2 in bilinguals) was compared with the number of subjects with other dominance patterns. Since some of the cells contained a small number of subjects, the Fisher Exact Probability Test (Bradley, 1968; Siegel, 1956) was used and the results showed that the individual laterality patterns for the two groups were not statistically different (E, = .26). Our previous visual and auditory laterality studies yielded similar results. * For the Bilinguals in the Portuguese set: Talking [F(l, 60) = 14.27, p < .Ol]; Reading Aloud [F(l, 60) = 14.01, p < .Ol]; Silent Reading [F(l, 60) = 2.10, n.s.1; Thinking [F(l, 60) = 1.75, n.s.1; and Reciting Automatisms [F(l, 60) = 12.16, p < ,011.
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GENERAL DISCUSSION Two main points can be made regarding language lateralization in bilinguals. The first is that bilinguals, as a group, do not differ from monolingual controls in terms of overall level of left-hemisphere dominance for language. The second point is that the bilinguals’ Ll (Portuguese) and L2 (English) do not differ in terms of overall left-hemisphere lateralization even though this group of bilinguals learned L2 in their adolescence, and hence are late bilinguals. These results together with those of our previous visual and auditory laterality tasks provide strong evidence for similar levels of left-hemisphere dominance for language in bilinguals and monolinguals . These findings are in agreement with those reported by Hynd et al., (1980) in that similar levels of left-hemisphere lateralization for the bilinguals’ L2 and monolinguals were found. On the other hand, the present results are quite different from those obtained by Sussman et al. (1982), who found that bilinguals showed weaker levels of left-hemisphere lateralization than monolinguals for both Ll and L2. In addition, while early bilinguals in their study demonstrated similar levels of weak lefthemisphere advantage for Ll and L2, late bilinguals showed left-hemisphere advantage for Ll, but bilateral control for L2. There are a number of differences between the present study and that of Sussman et al. which may well account for the contradictory results. First, the experimenters in Sussman et al. did not always speak the bilinguals’ language other than English and hence when the bilinguals performed verbal tasks they did so in an unnatural sociolinguistic context. In the present study, the experimenter spoke both the bilinguals’ languages and the topics chosen were appropriate to those languages. Second, in Sussman et al. half of the bilinguals were over 30 years old, and over 20% were 40 years old. The monolingual control group did not cover this same age range. In the present study, the bilinguals and monolinguals were matched for age. And, third, in Sussman et al., some 70% of the late bilinguals were American-born English speakers who learned their second language in an English-speaking environment. In contrast, the bilinguals in the present study learned each of their languages in their respective natural environments. In summary, the present study using the concurrent activities paradigm and our previous experiments using visual and auditory language laterality tasks provide converging evidence for a level of left-hemisphere language processing in bilinguals that is the same as in monolinguals. Recent studies using the dichotic listening technique (Galloway, 1981; Gordon, 1980; Gordon 8z Zatorre, 1981) extend the present findings to include adult bilinguals of varying degrees of fluency, varying degrees of second language usage, and to bilingual children. All of these studies show that
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left-hemisphere lateralization for language is the prevalent pattern in bilinguals as it is in monolinguals. REFERENCES Albert, M. L., & Obler, L. K. 1978. The bilingual brain. New York: Academic Press. Bradley, J. V. 1968. Distribution-free stutisrical tests. Englewood Cliffs, NJ: PrenticeHall. Pp. 199-201. Bryden, M. P. 1977. Measuring handedness with questionnaires. Neuropyschologia, 15, 617-624. Galloway, L. 1981. Contributions of the right cerebral hemisphere to language and communication: Issues on cerebral dominance with special emphasis on bilingualism, second language acquisition, sex differences, and certain ethnic groups. Doctoral dissertation, Department of Linguistics, University of California, Los Angeles. Galloway, L. 1982. The convolutions of second language learning: Towards a neuropsychological model of bilingualism and second language performance, a theoretical article with a critical review of current research and some new hypotheses. Language Learning, 31, 439-464.
Gordon, H. W. 1980. Cerebral organization in bilinguals. I. Lateralization. Bruin and Language, 9, 255-268. Gordon, D. P., & Zatorre, R. J. 1981. A right-ear advantage for dichotic listening in bilingual children. Brain and Language, 13, 389-396. Hynd, G. W., Teeter, A., & Stewart, J. 1980. Acculturation and the lateralization of speech in the bilingual Native American. International Journal of Neuroscience, 11, l-7. Kinsboume, M. 1982. Neuropsychological aspects of bilingualism. In H. Winitz (Ed.), Native language and foreign language acquisition. Annals of the New York Academy of Sciences,
379,
50-58.
Kinsboume, M., & Cook, J. 1971. Generalized and lateralized effects of concurrent verbalization on a unimanual skill. Quarterly Journal of Experimental Psychology, 23, 341-345. Kinsboume, M., & Hicks, R. F. 1978. Functional cerebral space: A model for overflow, transfer, and interference effects in human performance. In J. Requin (Ed.), Attention and performance, VIZ. Hillsdale, NJ: Erlbaum. Pp. 345-362. Kinsboume, M., & Hiscock, M. 1977. Does cerebral dominance develop? In S. J. Segalowitz & F. A. Gruber (Eds.), Language development and neurological theory. New York: Academic Press. Pp. 171-191. Obler, L., Zatorre, R., Galloway, L., & Vaid, J. 1982. Cerebral lateralization in bilinguals: Methodological issues. Brain and Language, 15, 40-54. Oldfield, R. C. 1971. The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, 97-113. Paradis, M. Bilingualism and aphasia. 1977. In H. Whitaker & H. A. Whitaker (Eds.), Studies in neurolinguistics, New York: Academic Press. Vol. 3, pp. 65-121. Siegel, S. 1956. Nonparametric statistics. New York: McGraw-Hill. Pp. 96-101. Soares, C. 1982.Converging evidence for left hemisphere language lateralization in bilinguals. Neuropsychologia, 20, 653-659. Soares, C., & Grosjean, F. 1981. Left hemisphere language lateralization in bilinguals and monolinguals. Perception and Psychophysics, 29, 599404. Sussman, H. M., Franklin, P., & Simon, T. 1982. Bilingual speech: Bilateral control? Bruin and Language, 15, 125-142. Vaid, J. 1983. Bilingualism and brain lateralization. In S. J. Segalowitz (Ed.), Language functions and brain organization. New York: Academic Press. Vaid, J., & Genesee, F. 1980. Neuropsychological approaches to bilingualism: A critical review. Canadian Journal of Psychology, 34, 419-447.