Fingerspelling, signed language, text and picture processing in deaf native signers: The role of the mid-fusiform gyrus

In fingerspelling, different hand configurations are used to represent the different letters of the alphabet. Signers use this method of representing written language to fill lexical gaps in a signed language. Using fMRI, we compared cortical networks supporting the perception of fingerspelled, signed, written, and pictorial stimuli in deaf native signers of British Sign Language (BSL). In order to examine the effects of linguistic knowledge, hearing participants who knew neither fingerspelling nor a signed language were also tested. All input forms activated a left fronto-temporal network, including portions of left inferior temporal and mid-fusiform gyri, in both groups. To examine the extent to which activation in this region was influenced by orthographic structure, two contrasts of orthographic and non-orthographic stimuli were made: one using static stimuli (text vs. pictures), the other using dynamic stimuli (fingerspelling vs. signed language). Greater activation in left and right inferior temporal and mid-fusiform gyri was found for pictures than text in both deaf and hearing groups. In the fingerspelling vs. signed language contrast, a significant interaction indicated locations within the left and right mid-fusiform gyri. This showed greater activation for fingerspelling than signed language in deaf but not hearing participants. These results are discussed in light of recent proposals that the mid-fusiform gyrus may act as an integration region, mediating between visual input and higher-order stimulus properties.