Selection versus association strength and the role of the left inferior prefrontal cortex in the retrieval of the semantic and phonological information

Thompson-Schill et al. (1997, 1998) proposed that the activation in the left inferior frontal gyrus (IFG) during verb generation was due to the selection of information among competing alternatives. The present study took into account both the effects of selection demands and association strength during retrieval using a semantic retrieval task---verb generation and a phonological retrieval task---stem completion. The results from healthy older adults and undergraduate subjects showed that association strength rather than selection demands influenced the retrieval of semantic and phonological information. A semantic STM deficit patient ML, with left IFG damage, showed great difficulty in verb generation especially when the association strength was weak. A phonological STM deficit patient JJ, with damage in temporo-parietal regions, showed much better performance. These results suggested that the left IFG is responsible for semantic retrieval, with the degree of involvement mediated by association strength between cue and target