Modality independence of word comprehension

Abstract

Functional magnetic resonance imaging (fMRI) was used to examine the functional anatomy of word comprehension in the auditory and visual modalities of presentation. We asked our subjects to determine if word pairs were semantically associated (e.g., table, chair) and compared this to a reference task where they were asked to judge whether word pairs rhymed (e.g., bank, tank). This comparison showed task-specific and modality-independent activation for semantic processing in the heteromodal cortices of the left inferior frontal gyrus (BA 46, 47) and left middle temporal gyrus (BA 21). There were also modality-specific activations in the fusiform gyrus (BA 37) for written words and in the superior temporal gyrus (BA 22) for spoken words. Our findings are consistent with the hypothesis that word form recognition (lexical encoding) occurs in unimodal cortices and that heteromodal brain regions in the anterior as well as posterior components of the language network subserve word comprehension (semantic decoding).

Figure 1

Activation maps of task differences for the visual modality. Letters label regions of interest. Solid black indicates areas of significantly more activation in the meaning than in the rhyming task (A: inferior frontal gyrus; B: middle temporal gyrus). Black borders indicate areas of overlapping activation between the meaning and the rhyming tasks. The left side of the brain is on the left.

Figure 2

Activation maps of task differences for the auditory modality. Letters label regions of interest. Solid black indicates areas of significantly more activation in the meaning than in the rhyming task (A: inferior frontal gyrus; B: middle temporal gyrus). Black borders indicate areas of overlapping activation between the meaning and the rhyming tasks. The left side of the brain is on the left.

Figure 3

Activation maps for task differences that are independent of modality. Letters label regions of interest. Solid black indicates areas of significantly more activation in the meaning than in the rhyming task. (A: inferior frontal gyrus; B: middle temporal gyrus). Black borders indicate areas of significantly more activation in the rhyming than in the meaning task. (C: middle to posterior cingulate gyrus; D: supramarginal gyrus). The left side of the brain is on the left.