Newopsychologio, Vol. 20, No. 6, Pp. 653459, 1982. Printed in Great Britain.

C028-3932/82/06065347$03.00/0 Q 1982 Pergamon Press Ltd.

CONVERGING EVIDENCE FOR LEFT HEMISPHERE LANGUAGE LATERALIZATION IN BILINGUALS*

CARLOS SOARES?

Psychology Department, 282 NI, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, U.S.A.

(Received 24 June 1982)

Abstract-A previous study [l] demonstrated that when subject and experimental variables are controlled, similar levels of left hemisphere language lateralization are obtained in bilinguals and monohnguals. The present study used the same group of bilinguals (adult, late acquirers of their second language) in an auditory lateralization task. A similar degree of left hemisphere asymmetry was again obtained for the bihnguals’ two languages and for the monolinguals. Furthermore, the individual performances of the bilinguals-within the present task and across visual and auditory tasks-paralleled those of monohnguals. Thus, converging evidence is provided for equal levels of left hemisphere language dominance in bilinguals and monolinguals.

INTRODUCTION

RECENT reviews of case reports of brain-damaged patients and of experimental studies obtained with normal subjects suggest that there may be a greater degree of right hemisphere involvement in the language processing of bilinguals than the level typically found in monolinguals [24]. If this were the case, theories of neuropsychology would have to postulate the emergence, or existence, of right hemisphere mechanisms which could be activated when learning and using a second language. However, the evidence cited in support of greater right hemisphere involvement in the language processing of bilinguals is open to criticism at several levels.

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 post- injury levels oflanguage proficiency [S]. It is also likely that the published studies constitute a biased sample of “unusual” cases [3, 63. Finally, a number of non-neurological factors may account for the differential effects of brain damage on the bilingual’s languages during the aphasic stage as well as during the recovery process. These factors include language fluency, frequency and recency of language usage, language used in recovery setting, language used during therapy, social and affective value of the languages, written form of the language, etc.

C3, 7, 81. Secondly, the experimental studies of normal bilinguals using auditory lateralization

paradigms have yielded mixed results. Some studies show right hemisphere advantage for one or both languages, especially in late bilinguals-those who acquire a second language after 12 yr of age [9915]. At the same time, other research provides evidence for left

*This research is part of the author’s Ph.D dissertation. tRequests for reprints should be sent to the author at the Department of Psychology and Social Relations, 1202

William James Hall, Harvard University, 33 Kirkland St., Cambridge, MA 02138, U.S.A.

653

654 CARLOS SOARES

hemisphere lateralization for language in bilinguals similar to that found in monolinguals [3, 16-191. However, in general, these experimental studies have not controlled for potentially confounding variables such as the sex and the language proficiency of the subjects, have failed to include a monolingual comparison group, and have committed errors in statistical analysis [20].

SOARES and GROSJEAN [ 11, using a tachistoscopic lateralization task, demonstrated that when the potential confounding variables are controlled, similar levels of left hemisphere advantage are obtained in the language processing of bilinguals and monolinguals. They found a right visual field effect for both bilinguals and monolinguals and observed that the

degree of left hemisphere asymmetry in bilinguals held up across mixed-language and separate-language presentation blocks. Finally, they found that the bilinguals in the separate-languages group did not differ from the monolinguals in overall reaction time.

The purpose of the present study was to replicate these results in an auditory lateralization task. To do this, the same stimuli, the same languages, and the same bilingual subjects were used as in the previous tachistoscopic study [l]. Apparently, this the first time that the same group of bilinguals has been tested in visual and auditory lateralization tasks. Research with

monolinguals has found that while main effects can be replicated for the same group of subjects across visual and auditory lateralization tasks, the patterns of lateralization for individual subjects can vary across tasks [21&24]. However, no comparable data are available so far for bilingual subjects. If the results obtained in the tachistoscopic study were to be replicated here, converging evidence would be provided for the position that bilinguals and monolinguals are similarly left lateralized for language.

Subjects

METHOD

Eighteen male Portuguese English bilinguals (ages 20 35 yr; mean=24.2 yr) whose first language was Portuguese and who first came into contact with English after the age of 12 yr, and nine male English-speaking monohnguals (ages 20.-24 yr; mean = 21.3 yr) participated in this study. All subjects were strong righthanders. as determined by a short questionnaire developed from BRYDEK [25] and OLDFILI.D [26], with no lefthanders in the immediate family. The bilinguals, who had all taken part in the SOARES and GROSJEAN visual lateralization study [ 11, were selected for approximately equal and high fluency in Portuguese and English. Their fluency was assessed by a questionnaire in which the subjects rated their fluency in reading, writing, speaking and understanding of Portuguese and English; a reading test in which subjects were timed while reading aloud Portuguese and English passages of equal length; 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 English and Portuguese equally, read the passages in approximately the same time (i lo”,,), and name approximately the same number of objects (+ 15”,,). In addition, care was taken to ensure that the bilinguals used both languages on a nearly daily basis. All of the bilmguals moved to the United States in their adolescence and, therefore, learned English in school and through their mteractions with English-speaking friends and the community in general.

Stimuli

The words used as stimuli---the same as those in SOARES and GROSJEAN [ l]+were forty English nouns of medium to high frequency (mean= 100.5; range, 10 371 according to the analysis by KLTC‘ERA and FRANCIS [27], and their Portuguese translations. The words (one to three syllables long) were spoken by a female bilingual fluent in both Portuguese and English and recorded on a Crown SS800 tape recorder using an AKG D200F microphone in a sound attenuating booth. The stimuli were then dubbed onto either the right or the left channel of the stimulus tape with a 10 set interval of white noise between words.

The bilingual subjects weredivided into two groups, as in the previous tachistoscopic study. For onegroup ofnine bilinguals, the Portuguese and the English words and ear ofpresentation were randomly mixed (BiMix group), This group received a series of 36 practice trials with an equal number of Portuguese and English words and an equal

LEFT HEMISPHERE LANGUAGE LATERALIZATION IN BILINGUALS 655

number of presentations to the left and to the right ear. For the second group of bilinguals, the Portuguese and the English words were presented in separate blocks (BiSep group), but within each language block ear presentation was random. Preceding each language block there were 18 practice trials in the appropriate language with an equal number of presentations to the right and to the left ear. Five of the subjects heard the English words first and the remaining subjects heard the Portuguese words first. The monolingual subjects (Mono group) were exposed only to the English words and received 18 practice trials with an equal number of presentations to the right and to the left ear. For half of the subjects the headphones were reversed in order to balance out any channel differences.

Each word was presented monaurally, once to the right ear and once to the left ear by a Revox B77 tape recorder through Koss K/6ALC headphones at 80 dB SPL against 65 dB background noise. Order of word presentation to right and left ears was random. All subjects were instructed to say the word presented on the stimulus tape as fast as possible. Reaction times were measured by a PDPl 1 computer as the time from the onset of the stimulus word triggered by a voice-operated relay to the onset ofthe subject’s vocalization which triggered a second voice-operated relay.

RESULTS AND DISCUSSION

The results for the two bilingual groups were analyzed separately. Figure 1 (top) presents the mean reaction times (RTs) for the words presented to each ear for the Mono controls and for the BiMix group. RTs to correct responses were analyzed in two analyses of variance. In one analysis, RTs to the English words for the two groups were examined (2 Groups [monolingual and bilingual] by 2 Ears [right and left], with Subjects and Words as random variables [28]). Both Group and Ear main effects were significant. First, the Mono controls

1150 1

RE LE RE LE RE LE MONOLINGUALS BILINGUALS

Mixed Language Presentation

s 950 -5 :: 900

g 850

m BOO .c

; 750

2

i RE LE RE LE LE az MONOLINGUALS BILINGU~:

Separate Language Presentation

FIG. 1. (Top) Mean reaction time (+ 1 SE.) to words presented to the right or to the left ear for monolinguals and bilinguals in the mixed-languages group. (Bottom) Same but for bilinguals in the separate-languages group. Reaction time was measured from the onset of the stimulus word to the

onset of the subject’s repetition of that word.

656 CARLOS SOARES

were significantly faster than the BiMix group in overall RT [F’ (1,16) = 4.75, P < 0.051. This longer latency in responding is apparently due to the subjects’ not knowing on any one trial the language of the stimuli. When the languages are presented separately (below), RTs for bilinguals and monolinguals are identical. And, second, responses were significantly faster to words presented to the right ear [F’ (1, 34) = 12.99, P < O.OOl]. This is taken to indicate left hemisphere superiority in this task. The Group by Ear interaction was not significant showing that although the bilinguals responded slower than the monolinguals in this isolated word task, the degree of left hemisphere advantage for language processing is identical for the two groups. Indeed, ratios of the mean RTs for right and left ear (R RT RE/X RT LE) clearly illustrate this point: Mono = 0.94; BiMix (English) = 0.94.

The performance of the bilinguals in their two languages was examined in a second analysis of variance [2 Languages (Portuguese and English) by two Ears (right and left), with Subjects and Words as random variables]. Only the Ear main effect was significant. Responses were significantly faster to words presented to the right ear [F’ (1, 35)= 10.53, P<O.Ol], again indicating left hemisphere superiority. Neither the language main effect nor the Language by Ear interaction reached significance demonstrating that the bilinguals as a group were equally fluent in both languages and had similar levels of left hemisphere dominance for their two languages. RE/LE ratios of mean RTs again illustrate this point: English = 0.94; Portuguese = 0.93.

The mean RTs for responses to words presented to each ear for the BiSep group and the Mono controls are shown at the bottom of Fig. 1. This set of results was analyzed in the same manner as those for the BiMix group. The analysis of variance comparing the Mono with the BiSep RTs for English words yielded only a significant Ear main effect. Once again, faster RTs were obtained for words presented to the right ear [F’ (1,34) = 16.02, P <O.OOl]. Neither the Group main effect nor the Group by Ear interaction reached significance indicating that: (1) when the bilinguals’ two languages were presented separately, the bilinguals performed essentially as monolinguals and, (2) identical levels of left hemisphere superiority were found for bilinguals and monolinguals. The RE/LE ratios for both groups were 0.94. The analysis of variance examining the performance of the BiSep group in Portuguese and English yielded the same pattern of results as that found in the BiMix group: only the Ear main effect was significant [F’ (1,32)= 11.95, P<O.Ol], with faster responses to words presented to the right ear. The failure of the Language main effect and of the Language by Ear interaction to reach significance indicates that listeners in this group of bilinguals, as those in the BiMix group, were equally fluent in the two languages and that both oftheir languages are lateralized to the same extent (RE/LE ratios: Portuguese=0.95; English=0.94).

Overall, this pattern of results replicates the main effects obtained in the visual

lateralization study by SOARES and GROSJEAN [l] where it was found that the responses of both the BiMix and the BiSep groups were faster to words presented to the right visual field. indicating left hemisphere superiority, and that the responses of the BiSep group did not differ from those of the Mono group. The converging evidence reached in the earlier study adds further support to the conclusion reached in the earlier study that when experimental variables are appropriately controlled, language processing in bilinguals is lateralized to the left hemisphere to the same extent as in monolinguals.

Analysis of individual performance showed that in the monolingual group one out of nine

subjects had essentially no hemispheric differences in the auditory-verbal task, while for the bilinguals two of the 18 subjects exhibited no hemispheric asymmetry in English and in Portuguese. Thus, the hemispheric dominance patterns for individual subjects are similar in

LETT HEMISPHERE LANciUAGE LATERALIZATION IN BILINGUALS 657

the two groups. Comparison of the performance of the bilinguals in the visual and the auditory lateralization tasks revealed that 72% of the subjects maintained lateralization patterns across tasks. This result is in line with those obtained in monolinguals where the percentage of subjects maintaining lateralization patterns across visual and auditory tasks has been found to range from around 60% [21,23] to 81% [22]. Taken together, these two analyses of individual performance demonstrate that the patterns for bilinguals across lateralization tasks are similar to those found in monolingual groups.

In summary, this study provides converging evidence for LH dominance in the processing of the bilinguals’ two languages. Further evidence comes from a new study that has just been completed [29]. As tachistoscopic and auditory methods of assessing hemispheric specialization only tap language processing at the word level, the same bilinguals were run on a concurrent activities, or time-sharing, paradigm which requires sentence-level processing. Identical results were again found for monolinguals and bilinguals. It appears, therefore,

that left hemisphere specialization for language is the prevalent pattern in groups of bilinguals, just as it is in monolinguals.

Acknowled,qements~ The author wishes to thank LINDA GALLOWAY, FRANCIS GROSJEAN, STEVE HARKINS. HARLAN LANE, JOANNE MILLER. L~RAINE OBLER. MICHAEL TERMAN and JOYTSNA VAID for their comments on earlier drafts of this manuscript, and HARTMUT TEUBER for assistance in computer programming. Part of this research was supported by grants from The Department of Health and Human Services Biomedical Research Support (RR07143) and from NIH (NS14923).

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1 I. HYND, G. W. and SCOTT, S. A. Propositional and appositional modes of thought and differential speech lateralization in Navajo Indian and Anglo children. Chi/d Der. 5, 909 -9 I I, 1980.

12. ROGERS, L., TENHOUTEN, W., KAPLAN, C. D. and GARDINER, M. Hemispheric specialization of language: an EEG study of bilingual Hopi Indian children. Int. J. Neurasci. 8, I-6. 1977.

13. SCOT-~, S., HYND, G. W., HUNT, L. and WEED, W. Cerebral speech lateralization in the native American Navajo. Neuropsycholoyia 17, 89-92, 1979.

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14. SCt~NEIDERMAN. E. and WESCHE, M. B. Right hemisphere participation in second language acquisition. Paper presented at the Third Los Angeles Second Language Research Forum, University ofcalifornia, Los Angeles. 19x0.

15. VAID. J. and LAMBERT. W. E. Cerebral involvement In the cognitive functiomng of bilinguals. Bruin Lcrrrc/. 8, 92-l IO. 1979.

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activities paradigm. Working Paper. Northeastern University. 19X2.

Une etude pr6alable wait montr6 que lorsque les variables li6eS au sujet et les variables experimentales sent contr616eS. on obtient des degr6s de latkalisation du langage dans 1'hCmisphPre gauche identiques pour les sujets parlant une seule langue et les sujets bilingues. Le travail actuel a port6 sur le m&w groupe de sujets bilingues (des adultes ayant acquis leur seconde langue tardivement), soumis i une tHche de latkalisation auditive. Un degr& semblable d'asym6trie en faveur de 1'hGmisphPre gauche a 6t6 obtenu de nouveau pour les deux langues chez les sujets bilinques, et aussi chez les sujets ne parlant qu'une seule lanque. En outre, les performances individuelle; des sujets bilingues dans cette tiche et dans d'autres tdches visuelles ou auditi- "es Se sent trouv6es voisines de celles des sujets ne parlant qu'une seule lanque. I1 existe done des preuves convergerites d'un 8aal dear6 de dominance de l'hEmisoh6re qauche DOW le langage' chez -1es sujets bilinques comme ch& ceux qui ne parlent qu'une settle lanque.

LEFT HEMISPHERE LANGUAGE LATERALIZATION IN RILINGI’ALS 659

Zusammenfassung:

Eine friihere Arbeit hatte gezelgt, da13 dam. wenn Versuchspersonen

und experimentelle Variable” kontrolliert sind, ein gleichartiges Niveau

van 1inkshemisphXrischer Sprachlateralisierung bei bilingualen und

monolingualen Sprechern gefunden wird. Die hier vorgelegte Unter-

suchung stiltetc sich auf dieselbe Gruppe van Bilingualen (Erwachsene,

welche die zwelte Sprache spBt erworben hatten) bei einer akustischen

Lateralisierungsaufgabe. Ein gleichartiges AusmaO linkshemisphlrischer

Asymmetric wurde wieder fiir die zwei Sprachen der Bilingualen und fiir

die Monolingualen gefunden. AuBerdem ware” die Leistungen der Bilingualen

bei der hier verwendeten Aufgabe und Uber visuelle und akustische Aufgaben -

denen der Monolmgualen gleich. Es werden also erneut Date” vorgelegt, die

gleiches Niveau der linkshemisphiirischen Sprachdominanz fiir bilinguale und

monolinguale Sprecher zeigen.