The neural correlates of sign versus word production

The production of sign language involves two large articulators (the hands) moving through space and contacting the body. In contrast, speech production requires small movements of the tongue and vocal tract with no observable spatial contrasts. Nonetheless, both language types exhibit a sublexical layer of structure with similar properties (e.g., segments, syllables, feature hierarchies). To investigate which neural areas are involved in modality-independent language production and which are tied specifically to the input-output mechanisms of signed and spoken language, we reanalyzed PET data collected from 29 deaf signers and 64 hearing speakers who participated in a series of separate studies. Participants were asked to overtly name concrete objects from distinct semantic categories in either American Sign Language (ASL) or in English. The baseline task required participants to judge the orientation of unknown faces (overtly responding 'yes'/'no' for upright/inverted). A random effects analysis revealed that left mesial temporal cortex and the left inferior frontal gyrus were equally involved in both speech and sign production, suggesting a modality-independent role for these regions in lexical access. Within the left parietal lobe, two regions were more active for sign than for speech: the supramarginal gyrus (peak coordinates: -60, -35, +27) and the superior parietal lobule (peak coordinates: -26, -51, +54). Activation in these regions may be linked to modality-specific output parameters of sign language. Specifically, activation within left SMG may reflect aspects of phonological processing in ASL (e.g., selection of hand configuration and place of articulation features), whereas activation within SPL may reflect proprioceptive monitoring of motoric output.