Do bilinguals have a different hemispheric lateralization in visual processing from monolinguals?

Bilinguals Have Different Hemispheric Lateralization in Visual Word Processing from Monolinguals Sze-Man Lam (fannylam@hku.hk) Janet Hui-wen Hsiao (jhsiao@hku.hk) Department of Psychology, University of Hong Kong Pokfulam Road, Hong Kong Abstract Previous bilingual studies showed reduced hemispheric asymmetry in visual tasks such as face perception in bilinguals compared with monolinguals, which suggested that hemispheric asymmetry in visual tasks could be modulated by experience in reading one or two languages. Here we examined whether difference in hemispheric asymmetry in visual tasks can also be observed in bilinguals who have different language backgrounds. We compared the behavior of three language groups in a tachistoscopic English word sequential matching task: English monolinguals (or alphabetic monolinguals, A-Ms), bilinguals with an alphabetic language L1 and English L2 (alphabetic-alphabetic bilinguals, AA-Bs), and bilinguals with a logographic language (Chinese) L1 and English L2 (logographic-alphabetic bilinguals, LA-Bs). The results showed that AA-Bs had a stronger right visual field/ left hemispheric (LH) advantage than A-Ms and LA-Bs, suggesting that different language learning experiences can influence how visual words are processed in the brain. In addition, we showed that this effect could be accounted for by a computational model that implements a theory of hemispheric asymmetry in perception (i.e. the Double Filtering by Frequency theory, Ivry & Robertson, 1998); the modeling data suggested that this difference may be due to both the difference in participants’ vocabulary size and the difference in word-to-sound mapping between alphabetic and logographic languages. Keywords: Hemispheric asymmetry; bilingualism; visual word recognition; computational modeling. Introduction Researchers have found different functional dominance between the two hemispheres. One of the most salient functional differences is the superiority of the left and right hemisphere (LH and RH) in language processing, especially in phonology processing (Corina, Vaid, & Bellugi, 1992), and in visuospatial processing and face processing (Kanwisher, McDermott, & Chun, 1997) respectively. Despite the converging evidences showing the RH superiority in specific tasks such as face recognition and visuospatial tasks, there have been studies showing reduced lateralization in these well-known RH tasks in bilinguals compared with monolinguals. Back in the 1980s, Sewell and Panou (1983) observed the typical right visual field (RVF)/ LH advantage in accuracy in an English word naming task in both bilinguals and monolinguals; in contrast, the typical left visual field (LVF)/ RH advantage in a spatial dot localization task was only found in monolinguals but not in bilinguals. In this task, a 4x5 grid with a dot in one of the boxes was shown unilaterally, and participants were required to report the location of the dot. Therefore, Sewell and Panou’s results (1983) suggested that the processing of some visual tasks such as spatial dot localization may be influenced by participants’ language experiences. About 20 years later, Hausmann et al. (2004) examined performance of bilinguals and monolinguals in visual tasks and found consistent results. They showed that in the accuracy data of both groups, a typical RVF/LH advantage was found in a sequential word-matching task whereas a typical LVF/RH advantage was found in a face detection task; however, the respond time data revealed a significant LVF/RH advantage in the face detection task only in monolinguals but not bilinguals. This result suggested that the RH visual processing abilities may be affected by language experience. The above results seemed to suggest that hemispheric asymmetry in RH dominant visual tasks such as face perception and spatial localization could be affected by language experience, but not for LH dominant visual tasks such as visual word recognition. However, some difference between the bilinguals and monolinguals was observed in Sewell and Panou’s study (1983). In their word naming task, words were presented unilaterally and the participants were required to report the word they perceived; the display time was 20ms and 40ms for monolinguals and bilinguals respectively. The authors selected these display times where the two groups made approximately the same number of errors. This suggested that bilinguals might process the words differently compared with monolinguals. In addition, in the word sequential matching task in which Hausmann, et al. (2004) did not find performance difference between bilinguals and monolinguals, a centrally presented word was followed by a unilaterally displayed word; the exposure time was 175ms for both groups. As the same display time was used for both groups and performance level between groups was not controlled, the results from the word sequential matching task of Hausmann, et al. (2004) might not completely reflect the difference between bilinguals and monolinguals in visual word processing. Therefore, in this study, we aim to control for the performance level in the sequential word matching task employed by Hausmann et al. (2004) for investigating the impact of language experience on hemispheric asymmetry in visual word recognition. Moreover, as all the previous studies investigated only the population of alphabetic language users, here we aim to investigate hemispheric asymmetry in visual word recognition in the following three groups of people with different language experiences: (1) alphabetic monolinguals (A-Ms), who know only one alphabetic language; (2)