Semantic processing in the right hemisphere may contribute to drawing inferences from discourse.

After listening to multiple-episode stories that promoted coherence inferences, right hemisphere-damaged patients answered Inference questions about the stories less accurately than Explicit questions, whereas normal elderly subjects answered both question types equally well. In addition, while subjects listened to the stories they made lexical decisions to tests words that were related to the promoted inferences or were unrelated to the stories. Right hemisphere-damaged patients responded more slowly to inference-related words than to unrelated words, whereas normal elderly subjects responded more quickly to interference-related words than to unrelated words. Furthermore, the episode boundaries did not affect either group's accuracy on Inference questions, and the boundaries equally affected both groups' lexical decision latencies, suggesting that the patients' inferencing deficit was not due to an impairment in organizing the mental substructures used to represent discourse. These results suggest that the right hemisphere-damaged patients lacked activation of semantic information necessary for drawing coherence inferences.