Are form priming effects phonological or perceptual? Electrophysiological evidence from American Sign Language.

Form priming has been used to identify and demarcate the processes that underlie word and sign recognition. The facilitation that results from the prime and target being related in form is typically interpreted in terms of pre-activation of linguistic representations, with little to no consideration for the potential contributions of increased perceptual overlap between related pairs. Indeed, isolating the contribution of perceptual similarity is impossible in spoken languages; there are no listeners who can perceive speech but have not acquired a sound-based phonological system. Here, we compared the electrophysiological indices of form priming effects in American Sign Language between hearing non-signers (i.e., who had no visual-manual phonological system) and deaf signers. We reasoned that similarities in priming effects between groups would most likely be perceptual in nature, whereas priming effects that are specific to the signer group would reflect pre-activation of phonological representations. Behavior in the go/no-go repetition detection task was remarkably similar between groups. Priming in a pre-N400 window was also largely similar across groups, consistent with an early effect of perceptual similarity. However, priming effects diverged between groups during the subsequent N400 and post-N400 windows. Signers had more typical form priming effects and were especially attuned to handshape overlap, whereas non-signers did not exhibit an N400 component and were more sensitive to location overlap. We attribute this pattern to an interplay between perceptual similarity and phonological knowledge. Perceptual similarity contributes to early phonological priming effects, while phonological knowledge tunes sensitivity to linguistically relevant dimensions of perceptual similarity.