Understanding ambiguous words in biased sentences: evidence of transient contextual effects in individuals with nonthalamic subcortical lesions and Parkinson's disease.

A cross-modal priming experiment was used to investigate lexical ambiguity resolution during sentence processing in individuals with nonthalamic subcortical lesions (NSL) (n = 10), compared to matched normal controls (n = 10), and individuals with cortical lesions (CL) (n = 10) and Parkinson's disease (PD) (n = 10). Critical sentences biased towards the dominant or subordinate meaning of a sentence-final lexical ambiguity were presented auditorily, followed after a short interstimulus-interval (ISI) (0 msec) or a long ISI (1000 msec), by the presentation of a visual target which was related to the dominant or subordinate meaning, or was an unrelated control word. Subjects made speeded lexical decisions on the targets. At the short ISI, lexical activation for the neurological patient groups appeared influenced by contextual information to a greater extent than in normal controls, which may indicate delayed lexical decision making or disturbed automatic lexical activation. At the long ISI, only the PD and NSL individuals failed to selectively activate the contextually appropriate meaning, suggesting a breakdown in the attention-based control of semantic activation through contextual integration. This finding may implicate disruptions to proposed frontal-striatal mechanisms which mediate attentional allocation and strategy formation.