LANGUAGE AS STRUCTURED SEQUENCES: A CAUSAL ROLE OF BROCA'S REGION IN SEQUENCE PROCESSING

In this thesis I approach language as a neurobiological system. I defend a sequence processing perspective on language and on the function of Broca's region in the left inferior frontal gyrus (LIFG). This perspective provides a way to express common structural aspects of language, music and action, which all engage the LIFG. It also facilitates the comparison of human language and structured sequence processing in animals. Research on infants, song-birds and non-human primates suggests an interesting role for non-adjacent dependencies in language acquisition and the evolution of language. In a series of experimental studies using a sequence processing paradigm called artificial grammar learning (AGL), we have investigated sequences with adjacent and nonadjacent dependencies. Our behavioral and transcranial magnetic stimulation (TMS) studies show that healthy subjects successfully discriminate between grammatical and non-grammatical sequences after having acquired aspects of a grammar with nested or crossed non-adjacent dependencies implicitly. There were no indications of separate acquisition/processing mechanisms for sequence processing of adjacent and nonadjacent dependencies, although acquisition of non-adjacent dependencies takes more time. In addition, we studied the causal role of Broca‟s region in processing artificial syntax. Although syntactic processing has already been robustly correlated with activity in Broca's region, the causal role of Broca's region in syntactic processing, in particular syntactic comprehension has been unclear. Previous lesion studies have shown that a lesion in Broca's region is neither a necessary nor sufficient condition to induce e.g. syntactic deficits. Subsequent to transcranial magnetic stimulation of Broca‟s region, discrimination of grammatical sequences with non-adjacent dependencies from nongrammatical sequences was impaired, compared to when a language irrelevant control region (vertex) was stimulated. Two additional experiments show perturbation of discrimination performance for grammars with adjacent dependencies after stimulation of Broca's region. Together, these results support the view that Broca‟s region plays a causal role in implicit structured sequence processing. LIST OF PUBLICATIONS I. Udden, J., Ingvar, M. , Hagoort, P., & Petersson, K. M. (2011). Implicit acquisition of grammars with crossed and nested non-adjacent dependencies: investigation the push-down stack model. Cognitive Science. In press II. Udden, J., Ingvar, M. , Hagoort, P., & Petersson, K. M. (2011). Implicit generalization in grammars with crossed non-adjacent dependencies. submitted manuscript III. Udden, J., Folia, V. , Forkstam, C. , Ingvar, M. , Fernandez, G. , Overeem, S. , van Elswijk, G. , Hagoort, P., & Petersson, K. M. (2008). The inferior frontal cortex in artificial syntax processing: An rTMS study. Brain Research, 1224, 69-78. IV. Udden, J., Ingvar, M. , Hagoort, P., & Petersson, K. M. (2011). Broca‟s region: a causal role in processing of grammars with adjacent and nonadjacent dependencies. submitted manuscript ADDITIONAL PUBLICATIONS I. Udden, J., Araujo, S. , Forkstam, C. , Ingvar, M. , Hagoort, P., & Petersson, K. M. (2009). A matter of time: Implicit acquisition of recursive sequence structures. Proceedings of the Cognitive Science Society, 2009, 2444-2449. II. Udden, J., Folia, V. , & Petersson, K. M. (2010). Neuropharmacology of Implicit Learning. Current Neuropharmacology. 8, 367–381. III. Gisselgard, J., Udden, J., Ingvar, M. , Petersson, K.M. (2006). Disruption of order information by irrelevant items: A serial recognition paradigm. Acta Psychologica. 124, 356-369 IV. Folia, V. , Udden, J., Forkstam, C. , Ingvar, M. , Hagoort, P., Petersson, K.M. (2008). Implicit learning and dyslexia. Annals of the New York Academy of Sciences. 1145, 132-50. V. Folia, V. , Udden, J., Forkstam, C. , Petersson, K.M. (2010). Artificial Language Learning in Adults and Children. Language Learning. 60 (S2), 188220.