Visual Field Asymmetries for Rhyme and Semantic Tasks in Fluent and Nonfluent Bilinguals

Visual Field Asymmetries for Rhyme and Semantic Tasks in Fluent and Nonfluent Bilinguals

Brain and Language 78, 53–61 (2001) doi:10.1006/brln.2000.2443, available online at http://www.idealibrary.com on Visual Field Asymmetries for Rhyme ...

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Brain and Language 78, 53–61 (2001) doi:10.1006/brln.2000.2443, available online at http://www.idealibrary.com on

Visual Field Asymmetries for Rhyme and Semantic Tasks in Fluent and Nonfluent Bilinguals A. Karapetsas and G. Andreou Laboratory of Neuropsychology, University of Thessaly, Volos, Greece Published online April 2, 2001

A tachistoscopic study investigated hemispheric specialization among fluent and nonfluent bilinguals for rhyme and semantic tasks in both their languages. Fluent bilinguals gave faster responses and made fewer errors in their responses to the words presented in the RVF(LH) while the opposite happened for nonfluent, which indicates greater RH participation in the first stages of a second language. Fluent bilinguals performed better not only in the second but also in their native language, suggesting superior language skills on the part of fluent bilinguals. A LVF(RH) superiority was obtained for semantic tasks, indicating RH participation in semantic judgments. Another finding was a high ratio of first-born children among fluent bilinguals, potentially explained in terms of parental attitudes toward first- versus later born children.  2001 Academic Press

It is by now a well-established finding that for most people, all right-handers and most left-handers, the left cerebral hemisphere (LH) is dominant for language. However, recent investigations suggest right-hemisphere (RH) involvement in certain components of language processing. Evidence for differential lateralization of language derives from clinical populations (Baynes, Funnel, & Fowler, 1994; Baynes, Tramo, & Gazzaniga, 1992; Reuter-Lorenz & Baynes, 1992; Zaidel, 1990) but studies with brain-intact individuals (Beeman & Chiarello, 1998; Chiarello, Senehi, & Soulier, 1986; Marsolek, Kosslyn, & Squire, 1992; Rodel, Cook, Regard, & Landis, 1992) concur with the clinical reports in suggesting that the left hemisphere is predominantly specialized for syntactic and phonetic component processes of language, while orthographic and semantic components are more bilaterally mediated. When one considers individuals who know more than one language, things are more complicated. A number of recent studies on bilinguals have explained the lateralization patterns for their two languages. So far, such studies have yielded contradictory results, probably because different languages might have different anatomical representations which would be determined by factors such as age of second language acquisition, level of second language proficiency, and manner of second language acquisition. Some studies point to greater left lateralization for second language when acquired during childhood (Genesee, 1983; Hynd, Teeter, & Stewart, 1980; Sussman, Franklin, & Simon, 1982; Vaid, 1983, 1987) while some others claim the opposite (Galloway & Krashen, 1980; Gordon, 1980; Silverberg, Gordon, Pollack, & Bentin, 1980). Address correspondence and reprint requests to An. Karapetsas, Laboratory of Neuropsychology, University of Thessaly, Argonafton-Filellinon Str., 38221 Volos, Greece. Fax: ⫹ 41 627853. 53 0093-934X/01 $35.00 Copyright  2001 by Academic Press All rights of reproduction in any form reserved.

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Some researchers have found that lateralization patterns for first and second languages do not differ significantly, irrespective of age (Ojemann, 1983, 1991; Paradis, 1981; Walters & Zatorre, 1978). Age of onset of bilingualism seems to enhance the sensitivity of the hemispheres to certain characteristics of the language. It has been proven that early bilinguals are better at making semantic comparisons while late bilinguals are better at making surface comparisons such as rhyme judgments (Eling, Marshall, & Van Galen, 1981; Vaid, 1983, 1987). Since the data concerning the role of age in second language lateralization were contradictory, some researchers claimed that proficiency in second language plays a more important role than age in differential involvement of the hemispheres in the processing of a second language (Cutler, Mehler, Norris, & Segui, 1989; Dehaene, Dupoux, & Mehler, 1997; Perani, Dehaene, Grassi, Cohen, Cappa, & Dupoux, 1996; Perani, Paulesu, Galles, Dupoux, Dehaene, Bettinardi, Cappa, Fazio, & Mehler, 1998; Schneiderman & Wesche, 1980). These studies suggest greater right-hemisphere (RH) processing of a second language at the early stages of language acquisition with decreasing RH participation with increased exposure to or acquisition of the second language. This is in agreement with previous studies that underline the role of the RH in the first stages of a new skill in general (Goldberg & Costa, 1981; Raichle, Fiez, Videen, MacLead, Pardo, Fox, & Petersen, 1994; Ross-Kossak & Turkewitz, 1986; Rourke, 1982). Proficiency in a second language has also been associated with cognitive development. Threshold theory (Cummins, 1976) maintains that bilinguals who achieve high levels of proficiency in both of their languages are cognitively more advanced than those with low level in one language or monolinguals. This theory has been proven by various researchers (Green, 1986; Karapetsas & Andreou, 1999; Ricciardelli, 1992; Tao & Healy, 1996). The manner of second language acquisition has also been found to play a role in the processing of the second language by the two hamispheres (Albert & Obler, 1978; Carroll, 1980; Gordon, 1980; Krashen, 1982). These studies claim that when the acquisition of the second language is done in an informal way, for example, at home by the parents, it depends more on the holistic capabilities of the RH. On the contrary, when the acquisition is done in a formal way, for example, at school, it depends more on the analytic capabilities of the LH. Sex has also been proven to have an effect on neurological organization of both first and second languages. Females as a group show weaker patterns of lateralization concerning both their first and second languages (Bryden & Mondor, 1992; Inglis, Ruckman, Lawson, Maclean, & Monga, 1982; McGlone, 1980). In addition, both sex and birth order seem to influence performance on tests of language and cognitive ability. It has been proven that females perform better than males on native and second language tests (Berninger & Fuller, 1992; Farhady, 1982; Halpern, 1986) and only- or first-born children perform better on reading tests and are generally superior to later born children on tests of language and cognitive ability (Beitchman & Inglis, 1991; Dowdney, Skuse, Morris, & Pickles, 1998; Glass, Neulinger, & Brim, 1974; Rosenblum & Dorman, 1978). Better language skills on the part of females is based on anatomical differences in the cerebral hemispheres of the two sexes but better performance of only- or first-born children on language tests can only be interpreted in terms of parental attitudes toward rearing only- or first- versus later born children, since there is more concern about children’s achievement for only- or first- versus later borns. Apart from other variables, task variables appear to influence patterns of lateralization. A LH superiority was obtained for rhyme tasks while the ability of the RH to find semantic relations between pairs of words was proven superior to that of the LH (Ardal, Donald, Meuter, Muldrew, & Luce, 1990; Beeman & Chiarello, 1998;

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Chiarello, 1991; Rayman & Zaidel, 1991; Roberts, 1997; Vaid, 1983, 1987). It has also been found that rhyme judgments, to the extent they are performed with recourse to phonetic cues, yield a LH superiority while, when the rhyme pairs are matched visually, a RH superiority can be obtained (Eling, Marshall, & Van Galen, 1981; Vaid, 1983; Zaidel & Peters, 1981). A number of different experimental techniques have been used to investigate functional asymmetries between the cerebral hemispheres. One of them is the technique of brief tachistoscopic presentation of stimuli to the left(LVF) or right(RVF) visual fields, which has been extensively used over the past several years (Chiarello, Maxfield, Richards, & Kahan, 1995; Faust & Babcoff, 1997; Magaro & Moss, 1989; Ortells, Tudela, Noguera, & Abab, 1998; Vaid, 1983, 1987; Young & Ellis, 1985). This technique relies on the structure of the afferent pathways within the visual system, which ensures that the material presented to either the LVF or RVF is delivered to the contralateral hemisphere. To ensure lateralized stimulus presentation, subjects are required to fixate on a central point with both their eyes or one eye covered in order to better control eye movements. Stimuli are then presented to either side of this point for short periods of time (e.g., 200–250 ms). In the above studies concerning lateralization in bilinguals, most researchers took into account the age of onset of bilingualism, others the manner of second language acquisition alone or in combination with age, and the fewest of them investigated the role that the level the subject has reached in second language plays in cerebral lateralization. The aim of the present study is to examine further the role of the level of the subject’s second language in cerebral lateralization.

METHOD

Subjects A total of 60 native Greek students (30 fluent and 30 nonfluent in English) from the University of Thessaly participated. All subjects had normal or corrected-to-normal vision. They were strongly righthanded as assessed by the Edinburgh Handedness Inventory (Oldfield, 1971) in its abridged version. The questionnaire comprised items pertaining to hand preference in writing, drawing, use of scissors, striking a match, and opening a box. The five items listed are sufficient for safe dichotomous classification into right-versus left-hand group according to Coren (1993). Subjects were divided into two groups according to language background. One group included 30 fluent English speakers (mean age of 23.2 years) and the other 30 nonfluent English speakers (mean age of 22.9). There was an equal number of males and females per group and all subjects from both groups acquired their second language formally (at school). Measure of fluency. Bilingual fluency was assessed by a combination of subjective and objective measures. We examined the subjects’ ability to speak and understand each language through a variety of tasks. We interviewed them and gave them instructions in both languages measuring the speed of response. The mean difference in performing our instructions between the two languages was not to exceed 10 s. We also counted how many words in both languages they could come up with when presented with pictures showing animals and various kinds of food, two word categories which are considered to assess verbal fluency. These word categories were previously used by researchers to assess bilingual fluency (Roberts, 1997) but also by researchers who wanted to assess the linguistic capacities in patients with RH damage (Chiarello & Church, 1986; Joanette & Goulet, 1988; Joanette, Goulet, & LeDorse, 1990). The mean difference in the number of words given per language was not to exceed 3. Bilingual fluency was also assessed by the subjects’ responses on a detailed questionnaire concerning their language background that included a school rating of their abilities in the native and second language and by the certificates they had obtained in the foreign language. Those who belonged to the fluent bilinguals had very good grades (mean: 19 of 20) in the Greek language at school and had obtained a professional degree in English (the Cambridge Certificate of Proficiency, the Michigan Certificate of Proficiency, or both) in the past 3 years. Nonfluent bilinguals had poor or medium grades (mean: 16 of 20) in the Greek language at school, never managed to take a degree in English, and had no English

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lessons in the past 3 years. The average age at which the subjects belonging to both groups reported beginning their study of their second language was 9 years, 4 months.

Materials and Procedure One ZETT ROYAL AFS 150 tach-projector (10 ms) was used to present the stimuli at a viewing distance of 57 cm. Each subject participated in 16 trials. A total of 240 words, half in Greek, half in English, were presented per visual field. Words per language were classified into 6 sets per visual field, each set containing a target word and 5 test words. The words were displayed horizontally to the right or to the left of the center of the screen, which was marked by a black circle. The gap between the fixation point and the inner edge of the word was 3 cm. The visual angle subtended by the gap was 2.86°. Subjects had either their right or left eye fixed on the circle while the other was covered. Their head was rested on a chin rest. Each trial began with instructions by the experimenter explaining the experimental task. Subjects were tested on both rhyme and semantic category matching conditions. They heard a target word and 1 s later there was a hearing signal, after which a test word was presented in either the left or right visual hemifield for a constant exposure of 200 ms. They placed their right index finger on the middle of a keyboard and were instructed to press the ‘‘1’’ key if the word presented on the screen rhymed with the word they had heard by the experimenter and the ‘‘2’’ key if the word did not rhyme. We followed the same procedure for the semantic task, in which the subject pressed the ‘‘1’’ key if the word presented on the screen had a semantic relationship with the one they heard by the experimenter and the ‘‘2’’ key if the word did not have a semantic relationship. Before the beginning of the actual trials, there were 10 training trials during which different stimuli were presented. These trials were not included in the statistical analysis.

Data Analysis Data were initially analyzed by a mixed-design analysis of variance (ANOVA) using language (Greek vs English), level (fluent vs nonfluent bilinguals), type of task (rhyme vs semantic), sex (males vs females), and visual field (left visual field-LVF vs right visual field-RVF) as factors. The dependent variables were reaction time (RT) and errors of lexical decisions to the target stimuli. Statistically significant interactions (p ⬍ .05) were further evaluated by post hoc Scheffe F test. A ⫻2 analysis was performed to compare birth order with fluency in foreign language. The SPSS statistical programme was used to analyse the data.

RESULTS

A within-subjects 2 (language: Greek vs English) ⫻ 2 (level: fluent vs nonfluent bilinguals) ⫻ 2 (type of task: rhyme vs semantic) ⫻ 2 (sex: males vs females) ⫻ 2 (VF: LVF vs RVF) mixed-design ANOVA revealed statistically significant (p ⬍ .05) main effects for type of task [F(2.000) ⫽ 39.909], visual field [F(2.000) ⫽ 11.335], and level [F(2.000) ⫽ 23.117], which interacted significantly with visual field [F(2.000) ⫽ 4.009], and a three-way interaction of level ⫻ language ⫻ type of task [F(2.000) ⫽ 7.497] was also obtained. No statistically significant main effect for language alone was found but there was a statistically significant interaction of language with type of task [F(2.000) ⫽ 22.812] and with sex [F(2.000) ⫽ 3.144]. Furthermore, a within-subjects mixed-design ANOVA (language ⫻ level ⫻ type of task ⫻ sex ⫻ visual field) was performed on both reaction time (RT) and errors. Mean reaction times and errors for all factors are presented in Table 1. The only statistically main effect for both errors and RT was obtained for level [errors: F(1) ⫽ 22.683, RT: F(1) ⫽ 33.495], indicating that fluent bilinguals generally made fewer errors than nonfluent bilinguals (2.51 vs 3.23) and were faster in giving their responses (1.00 vs 1.36 ms). A statistically main effect for errors was obtained for type of task [F(1) ⫽ 78.715], indicating that fewer errors were made for rhyme than semantic lexical judgments (2.20 vs 3.54) and for visual field [F(1) ⫽ 22.683], indicating that fewer errors were made for the words presented in the RVF than for those presented in the LVF (2.51 vs 3.23). No statistically significant main ef-

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TABLE 1 Mean RTs and Errors for Language Type of Task, Sex, and Visual Field in Fluent and Nonfluent Bilinguals

Fluent Bilinguals RT a Errors Nonfluent RT a Errors a

Greek

English

Rhyme

Semantic

Males

Females

LVF

RVF

1.00 2.76

1.03 2.25

1.03 2.20

1.09 2.29

1.02 2.42

1.06 2.60

1.08 2.98

1.00 2.03

1.36 3.18

1.45 3.27

1.14 2.26

1.17 2.31

1.17 3.49

1.46 2.97

1.14 3.00

1.17 3.45

Reaction time is in seconds.

fects were found for language and sex when taken alone but there was a two-way significant interaction of language ⫻ level for errors [F(1) ⫽ 3.964], a two-way significant interaction of language ⫻ type of task for errors [F(1) ⫽ 26.470] and RT [F(1) ⫽ 29.239], and a two-way significant interaction of language ⫻ sex for errors [F(1) ⫽ 5.483]. Two-way statistically significant interactions for errors were also obtained for level ⫻ sex [F(1) ⫽ 5.334] and type of task ⫻ VF [F(1) ⫽ 4.092] and there was also a three-way interaction of language ⫻ level ⫻ type of task [F(1) ⫽ 13.774]. Only one significant two-way interaction of level ⫻ VF was found for RT [F(1) ⫽ 6.987]. Post hoc Scheffe F test performed on both RT and errors of the above two-way and three-way significant interactions revealed the following results: Fluent bilinguals were faster than nonfluent bilinguals in giving their responses both in Greek (1.00 vs 1.36 ms) and in English (1.03 vs 1.45 ms) and also made fewer errors in English (2.25 vs 3.27 ms). RT was faster for English than Greek rhyme (1.01 vs 1.14 ms), for Greek than English semantic task (1.07 vs 1.16 ms), and for English rhyme than English semantic task (1.01 vs 1.16). Fewer errors were made for English than for Greek rhyme (1.71 vs 2.69) and for English rhyme than semantic task (1.71 vs 3.81). RT was generally faster for fluent males than nonfluent males (1.02 vs 1.17), especially in English (1.01 vs 1.15), and for fluent than nonfluent females (1.06 vs 1.46). Fluent males made generally fewer errors than nonfluent males (2.42 vs 3.49), especially in English (2.07 vs 3.24). Fluent bilinguals gave faster responses than nonfluent bilinguals to the words presented in the RVF (1.00 vs 1.17 ms) and their responses to the words presented in the RVF were faster than those presented in the LVF (1.00 vs 1.08). Fluent bilinguals made fewer errors in their responses to the words presented in the RVF than those presented in the LVF (2.03 vs 2.98) and their errors in the RVF were fewer than those made by nonfluent bilinguals in the same VF (2.03 vs 3.45). Fewer errors were made in the RVF for rhyme than for semantic judgments (1.99 vs 3.99), in the LVF for semantic than rhyme judgments (2.40 vs 4.05), and in the LVF than in the RVF for semantic judgments (2.40 vs 3.99). A two-way analysis performed to compare birth order with fluency in foreign language revealed a statistically significant (p ⬍ .05) ratio of first-born children among fluent bilinguals. Twenty-six of 30 fluent bilingual males and females were first-born. DISCUSSION

Our results confirmed earlier findings which showed that proficiency in second language plays the most important role in differential involvement of the hemispheres in the processing of both native and foreign language (Cutler, Mehler, Norris, & Segui, 1989; Dehaene, Dupoux, & Mehler, 1997; Perani, Dehaene, Grassi, Cohen,

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Cappa, & Dupoux, 1996; Perani, Paulesu, Galles, Dupoux, Dehaene, Bettinardi, Cappa, Fazio, & Mehler, 1998; Schneiderman & Wesche, 1980), since in our study the interaction between the level in second language and all the other factors was statistically significant. Nonfluent bilinguals made fewer errors in their responses to the words presented in LVF(RH) than those presented in the RVF(LH) while fluent bilinguals gave faster responses and made fewer errors than nonfluent bilinguals to the words presented in the RVF(LH). These findings lend support to previous studies which suggest greater RH participation in the processing of the foreign language at its early stages, as it usually happens with every new skill, and a greater LH participation at its advanced stages. In addition, fluent bilinguals were generally faster than nonfluent bilinguals in giving their responses not only in English but also in Greek, a finding which confirms earlier researchers claiming that bilinguals who attain a high level of proficiency in both languages perform better than bilinguals with a low level in one of the languages (Green, 1986; Karapetsas & Andreou, 1999; Ricciardelli, 1992; Tao & Healy, 1996). In our study, task variables were found to influence patterns of lateralization. Fewer errors were made in the RVF(LH) for rhyme than for semantic judgments and the opposite happened in the LVF(RH). This finding lends support to previous studies (Ardal, Donald, Meuter, Muldrew, & Luce, 1990; Beeman & Chiarello, 1998; Chiarello, 1991; Rayman & Zaidel, 1991; Roberts, 1997; Vaid, 1983a, 1987b), which claim an LH superiority for rhyme tasks, especially when performed with recourse to phonetic cues, as it happened in our experiments, and RH participation in semantic tasks. We found participation of both hemispheres in the processing of native and foreign language depending on the task, which contradicts other research (Albert & Obler, 1978; Carroll, 1980; Gordon, 1980; Krashen, 1982) claiming that the formal acquisition of a second language, as it happened in our study, depends on the analytic capabilities of the LH. This finding indicates that task variables seem to influence patterns of lateralization more than the way a language is acquired and whether a language is acquired formally or informally; it is the specific task that the subject performs which determines the differential participation of the hemispheres. A general tendency on the part of both fluent and nonfluent bilinguals to make fewer errors for rhyme than for semantic lexical judgments in both languages was also observed. No differences were found between the two groups, probably because all the subjects belonging to the two groups started studying their second language at about the same age. So, we agree with previous researchers who have claimed that age of onset of bilingualism influences patterns of cerebral lateralization but we contradict the finding (Eling, Marshall, & Van Galen, 1981; Vaid, 1983, 1987) that early bilinguals are better at making semantic comparisons and late bilinguals at making surface comparisons such as rhyme, unless the age limit of late onset of bilingualism is set under adolescence. Sex interacted significantly both with language and level, which means that it generally played a significant role in our results. However, post hoc analysis did not reveal any statistically significant differences between the sexes. The only differences we found concerned the RT and the number of errors made by fluent males compared to nonfluent males and fluent females compared to nonfluent females. Fluent bilingual males and females gave faster responses and made fewer errors than nonfluent males and females, especially in English, a result which is expected, since high levels of proficiency in English helped fluent bilinguals to find more correct responses to word stimuli and answer faster than nonfluent ones. Sex did not interact significantly with VF, which means that in our study sex did not influence patterns of lateralization directly but only when combined with other factors such as level or language. Our results show that sex has an effect on neurological organization of both first and second language but they are in contrast with other researchers who found that fe-

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males show weaker patterns of lateralization than males, suggesting that the influence of sex on lateralization happens through a complex interaction between several factors. We also found a relationship between second language proficiency and birth order. Twenty-six of 30 males and females who belonged to the fluent bilingual group were first-born while only 7 of 30 males and females who belonged to the nonfluent bilingual group were first-born. Our finding lends support to previous studies (Beitchman & Inglis, 1991; Dowdney, Skuse, Morris, & Pickles, 1998; Glass, Neulinger, & Brim, 1974; Rosenblum & Dorman, 1978) which claim that language skills and cognitive ability are superior in first-born compared to later born children. However, we agree partly with these studies because they found superior language skills not only in first-born but also in only-children, a finding we did not come up with in our study, and language superiority concerned only native language proficiency and not foreign language. The general superiority of first-born children in comparison to later born on tests of language ability can be interpreted in terms of parental attitudes toward rearing their first-born child compared to their later born children. The first child enjoys more concentrated attention and is rewarded more by his or her parents for distinctive actions and later on he or she serves as an interlocutor between his or her parents and later born siblings, a role which appears to be an excellent one for the development of verbal skills. To sum up, the present study provides evidence for bilingual subgroup differences in linguistic task performance and suggests that the level of proficiency in second language influences patterns of cerebral lateralization. We also found that birth order may contribute to successful or unsuccessful second language acquisition. Further research into the field of bilingualism, taking into account the level of second language proficiency alone or in combination with more factors such as age of onset of bilingualism or manner of second language acquisition may lead to useful conclusions concerning cerebral lateralization for native and second language.

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