Signed Words in the Congenitally Deaf Evoke Typical Late Lexicosemantic Responses with No Early Visual Responses in Left Superior Temporal Cortex

Superior temporal areas surrounding auditory cortex are active for both sign and speech during lexicosemantic processing, but only for speech during sensory processing. A, Grand average activity to signs at ∼100 ms in deaf subjects is localized to occipital cortex in calcarine and superior occipital sulci. B, Grand average activity to speech at ∼100 ms in hearing subjects is localized to posterior temporal cortex. C, Center, Grand average activity to incongruent–congruent signs at 300–350 ms (black arrow) in deaf subjects. Surrounding graphs, Regional time courses for congruent and incongruent conditions in five bilateral regions of interest from −100 to 600 ms (light blue arrow at 100 ms). D, Same as C for speech in hearing subjects. IPS, Intraparietal sulcus; PT, planum temporale; AI, anterior insula; STS, superior temporal sulcus; TP, temporal pole; V1, primary visual. All mapped activity is cluster thresholded dynamic statistical parametric maps, significantly greater than prestimulus baseline at p < 0.05, corrected.

Individual MEG sensors demonstrate the dissociation between early and late activity in auditory regions. A1, Head plot shows the location of a left superior temporal MEG channel showing significant incongruent > congruent activity in a deaf native signer. A2, The left superior temporal MEG channel shows the congruent versus incongruent difference for signs. B1, Head plot from a hearing participant. B2, The same channel shows a similar difference for speech in a single representative hearing participant. Both subjects begin to show a significant difference between conditions at ∼240 ms. C, The same channel shows a sensory peak at ∼100 ms for hearing (purple), but not deaf (green), subjects. Gray regions indicate significance at p < 0.01.