Thesis defense Joao Ferreira (Donders Series 602)

Inflectional encoding in language production: Inhibition and the basal ganglia

According to a prominent account of inflectional encoding (Pinker, 1999; Pinker & Ullman, 2002), regular forms are encoded by a rule-governed combination of stems and affixes, whereas irregular forms are retrieved from memory while inhibiting rule application. Importantly , this dual system account proposes that both rule application for regulars and inhibition for irregulars is subserved by the basal ganglia, as suggested by past tense productions deficits observed in Parkinson’s disease patients. In this dissertation, my first goal was to examine if inhibition is indeed a crucial process in verb inflection; my second goal was to explore the role of the basal ganglia in language production by looking at the literature on dysfunction of the basal ganglia; and my third goal was to investigate whether the production of the past tense of regulars and irregulars is subserved by distinct brain regions, if there was any basal ganglia involvement in this processes, and if any inhibitory regions were associated with irregular production. My main findings are that regulars and irregulars seem to be produced by different processes in different brain regions, but that there does not seem to be any inhibition nor basal ganglia involved in them.