fMRI investigation of sentence comprehension by eye and by ear: modality fingerprints on cognitive processes

The neural substrate underlying reading vs. listening comprehension of sentences was compared using fMRI. One way in which this issue was addressed was by comparing the patterns of activation particularly in cortical association areas that classically are implicated in language processing. The precise locations of the activation differed between the two modalities. In the left inferior frontal gyrus (Broca's area), the activation associated with listening was more anterior and inferior than the activation associated with reading, suggesting more semantic processing during listening comprehension. In the left posterior superior and middle temporal region (roughly, Wernicke's area), the activation for listening was closer to primary auditory cortex (more anterior and somewhat more lateral) than the activation for reading. In several regions, the activation was much more left lateralized for reading than for listening. In addition to differences in the location of the activation, there were also differences in the total amount of activation in the two modalities in several regions. A second way in which the modality comparison was addressed was by examining how the neural systems responded to comprehension workload in the two modalities by systematically varying the structural complexity of the sentences to be processed. Here, the distribution of the workload increase associated with the processing of additional structural complexity was very similar across the two input modalities. The results suggest a number of subtle differences in the cognitive processing underlying listening vs. reading comprehension.