1. Effects of Bilingualism on Hemispheric Interaction Suzanne E. Welcome & Christine Chiarello University of California, Riverside Maintaining and coordinating two languages requires more cognitive resources than maintaining a single language. There can be differences in the locus (e.g., Kim, Relkin, Lee & Hirsch, 1997) or extent (e.g. Hasegawa, Carpenter, & Just, 2002) of activation in a bilingual depending on the language used. Even if the areas activated by language tasks in each language are highly overlapping (e.g., Chee, Tan, & Thiel, 1999), control mechanisms may be utilized in the bilingual brain to prevent unwanted cross-language intrusions (Green, 1998). Experience coordinating two languages may impact non- linguistic aspect of cognition. Bilingual children show an advantage over monolingual children on card sorting tasks which involve switching from one set of rules to another (Bialystok & Martin, 2004). Bilinguals show a reduced right-hemisphere advantage on a face-discrimination task relative to monolinguals (Hausmann, Durmusoglu, Yazgan, & Gunturkun, 2004). Attentional resources may be managed by the degree of interhemispheric interaction. A more complex task that demands more processing power is completed more quickly when the relevant information is divided between the hemispheres; a less complex task that demands less processing power is completed more quickly when all the relevant information is directed toward a single hemisphere (Banich, 1998). Children with ADHD show morphological differences in the corpus callosum (Giedd, Blumenthal, Molloy, & Castellanos, 2001). Individuals with agenesis of the corpus callosum show decreased ability to shift spatial attention from one VF to another (Hines, Paul, & Brown, 2002). Methods The Name Identity and Letter Rhyme tasks cannot be done based on perceptual matching alone and will therefore require more resources than the Physical Identity task. Across-VF presentation should be advantageous for the Name Identity and Letter Rhyme tasks but not for the Physical Identity task. Because bilinguals have more experience in the recruitment of additional cognitive resources in response to language input, they will show increased efficacy of interhemispheric communication. Thus, bilinguals should perform better than monolinguals on across- VF trials. Bilinguals should have more experience in optimizing processing to match task demands than monolinguals. Therefore, bilinguals should show a greater task difference in the degree to which across- VF processing is beneficial. Predictions Experiment 1: Participants 64 right-handed undergraduates 32 monolinguals fluent only in English who were not exposed to a second language before age 10 32 fluent bilinguals who currently use both languages and were exposed to both languages before age 5 Stimuli & Presentation 2 Blocks of trials Physical Identity - less computationally complex Name Identity - more computationally complex 240 Experimental trials per block 120 Match Trials, half within visual field trials and half across visual field trials Experiment 2: Participants 64 right-handed undergraduates who did not participate in Experiment 1 (32 monolinguals and 32 bilinguals) Stimuli & Presentation Identical to Experiment 1 except that the Name Identity task was replaced by a Letter Rhyme Task Name Identity (Exp 1) Physical Identity Letter Rhyme (Exp 2) TH T HT T Within VFAcross VF HT t HB T TH t BH T HQ T HQ t HQ T No Match Results Experiment 1: A significant AHA was present for the more complex name identity task but not for the physical identity task. Physical Identity: no effect of across versus within-VF presentation on errors or RT Name Identity: error rate for within-VF trials (11.8%) was significantly higher than for across-VF trials (7.4%) and the RT for within-VF trials (858) was significantly longer than for across-VF trials (813) For accuracy, but not RT, the degree of AHA was more task-dependent for bilinguals than for monolinguals. Monolinguals: no interaction between task and across versus within-VF presentation for error rate Bilinguals: significant interaction between task and across versus within-VF presentation for error rate Experiment 2: A significant AHA was present for rhyme trials and a within-hemisphere advantage was present for physical identity trials. Physical Identity: RTs were faster for the within-VF trial (645 ms) than across-VF trials (659 ms) Letter Rhyme: error rate for within-VF trials (15.4%) was higher than for across-VF trials (12.0%) and the RT for within-VF trials (1632 ms) was longer than for across-VF trials (1569 ms) For accuracy only, the degree of AHA differs more between tasks for bilinguals than for monolinguals. Monolinguals: no interaction between task and across versus within-VF presentation for error rate Bilinguals: significant interaction between task and across versus within-VF presentation for error rate The more computationally complex name identity task and rhyme task resulted in a significant AHA; the less complex physical identity task did not. The hypothesis that bilinguals would perform better on across-VF trials was not supported by the data. The error rate measure indicated that the task difference in degree of AHA was larger for bilinguals than monolinguals. Bilinguals appear to be more able to optimize interhemispheric processing in response to task complexity so that the accuracy difference between the simple and complex tasks is magnified relative to monolinguals. Bilinguals appear to show an enhanced ability to match processing to task demands by recruiting more interhemispheric resources as task complexity increases. Conclusions Across Hemisphere Advantage (AHA) Degree to which performance is enhanced when relevant information is divided between hemispheres Calculated as percent error/RT (within VF - across VF) Banich, M. (1998). The missing link: the role of interhemispheric interaction in attentional processing. Brain and Cognition, 36, 128-157 Bialystok, E, & Martin, M. M. (2004) Attention and inhibition in bilingual children: evidence from the dimensional change card sort task. Developmental Science, 7(3), 325-339 Chee, M. W. L., Tan, E. W. L., & Thiel, T. (1999). Mandarin and English single word processing studied with functional magnetic resonance imaging. The Journal of Neuroscience, 19(8), 3050-3056 Green, D.W. (1998) Mental control of the bilingual lexico-semantic system. Bilingualism: Language and Cognition, 1, 67-81 Giedd, J. N., Blumenthal, J., Molloy, E., & Castellanos, F. X. (2001) Brain imaging of attention deficit/hyperactivity disorder. Annals of the New York Academy of Science, 931, 33-49 Hasegawa, M., Carpenter, P. A., Just, M. A. (2002) An fMRI study of bilingual sentence comprehension and workload. NeuroImage, 15, 647-660 Haussmann, M. Durmusoglu, G., Yazgan, Y., Gunturkun, O. (2004) Evidence for reduced hemispheric asymmetries in non-verbal functions in bilinguals. Journal of Neurolinguistics, 17 285-299 Hines, R. J., Paul, L. K., & Brown, W. S., (2002) Spatial attention in agenesis of the corpus callosum: shifting attention between visual fields. Neuropsychologia, 40, 1804-1814 Kim, K. H. S., Relkin, N. R., Lee, K, & Hirsch, J. (1997). Distinct cortical areas associated with native and second languages. Nature, 388, 171-174 References Introduction This research was partially supported by NSF grant BCS-0079456 and NIH grant DC006957 to Christine Chiarello.