Effects of sign language experience on categorical perception of dynamic ASL pseudosigns.

We investigated effects of sign language experience on deaf and hearing participants' categorical perception of minimal manual contrast stimuli that met key criteria of speech perception research. A continuum of meaningless dynamic stimuli was created with a morphing approach, which manipulated videorecorded productions of phonotactically permissible pseudosigns differing between American Sign Language (ASL) handshapes that contrast on a single articulatory dimension (U-V: finger-spreading). AXB discrimination and AXB categorization and goodness ratings on the target items were completed by deaf early (native) signers (DE), deaf late (nonnative) signers (DL), hearing late (L2) signers (HL), and hearing nonsigners (HN). Categorization and goodness functions were less categorical and had different boundaries for DL participants than for DE and HL participants. Shape and level of discrimination functions also differed by ASL experience and hearing status, with DL signers showing better performance than DE, HL, and especially HN participants, particularly at the U end of the continuum. Although no group displayed a peak in discrimination at the category boundary, thus failing to support classic categorical perception, discrimination was consistent with categorization in other ways that differed among the groups. Thus, perception of phonetic variations underlying this minimal sign contrast is systematically affected by language experience.