Categorical perception in American Sign Language

Abstract

Categorical perception (CP) refers to the finding that certain stimuli (particularly speech) are perceived categorically rather than continuously, despite a continuous variation in form. Two experiments investigated whether Deaf signers or hearing nonsigners exhibit CP for hand configuration or for place of articulation (the location of articulation on the body) in American Sign Language (ASL). CP performance was measured using discrimination (ABX) and categorisation paradigms with computer-generated images of signs. In the categorisation task, signers and nonsigners exhibited sigmoidal performance and categorised non-identical stimuli together at each end of the perceptual continuum for both hand configuration and place of articulation, regardless of phonological distinctiveness in ASL. The finding that signers and nonsigners performed similarly suggests that these categories in ASL have a perceptual as well as a linguistic basis. Results from the discrimination task, however, showed that only ASL signers demonstrated categorical perception, and only for phonologically contrastive hand configuration. Neither group exhibited CP for place of articulation. Lack of a CP effect for place of articulation may be due to more variable category boundaries. A CP effect for contrastive hand configuration suggests that deaf signers develop special abilities for perceiving distinctions that are relevant to American Sign Language.