Effects of language experience on the perception of American Sign Language

Abstract

Perception of American Sign Language (ASL) handshape and place of articulation parameters was investigated in three groups of signers: deaf native signers, deaf non-native signers who acquired ASL between the ages of 10 and 18, and hearing non-native signers who acquired ASL as a second language between the ages of 10 and 26. Participants were asked to identify and discriminate dynamic synthetic signs on forced choice identification and similarity judgement tasks. No differences were found in identification performance, but there were effects of language experience on discrimination of the handshape stimuli. Participants were significantly less likely to discriminate handshape stimuli drawn from the region of the category prototype than stimuli that were peripheral to the category or that straddled a category boundary. This pattern was significant for both groups of deaf signers, but was more pronounced for the native signers. The hearing L2 signers exhibited a similar pattern of discrimination, but results did not reach significance. An effect of category structure on the discrimination of place of articulation stimuli was also found, but it did not interact with language background. We conclude that early experience with a signed language magnifies the influence of category prototypes on the perceptual processing of handshape primes, leading to differences in the distribution of attentional resources between native and non-native signers during language comprehension.

Introduction

Deaf individuals, unlike hearing individuals, vary considerably in the age of exposure to their first language. Auditory deprivation prevents exposure to a spoken language from birth, and a variety of social and demographic patterns prevent exposure to a signed language from birth for more than 90% of deaf individuals. Children who are exposed to a signed language from birth reach all of the language development milestones at similar ages to children acquiring spoken languages (Bonvillian and Folven, 1993, Newport and Meier, 1985, Petitto and Marentette, 1991). As adults, these individuals perform significantly better than deaf adults exposed to signed languages at later ages across a variety of language tasks. There is wide-ranging evidence that the variability in age of exposure to a signed language is related to language performance in adulthood (Boudreault and Mayberry, 2006, Emmorey et al., 1995, Emmorey and Corina, 1990, Mayberry, 1993, Mayberry and Fischer, 1989, Morford, 2003, Newport, 1990). What is not yet clear is whether age of exposure to a signed language affects all aspects of language acquisition and processing, or whether poor performance on a range of language tasks reflects difficulties with specific processes only. Mayberry (1994:84) hypothesized that disruptions in phonological processing may have cascading effects upon subsequent stages of sign language comprehension. This study takes a first step toward investigating this hypothesis by isolating sign perception from other components of sign language processing.

American Sign Language (ASL) is the primary language used in the Deaf² communities of the United States and parts of Canada. It has a lexicon and grammar that are distinct from the spoken languages in use in the same communities (e.g., English). ASL is also distinct from other signed languages (e.g., British Sign Language). Signed languages exhibit a level of structure that has been analyzed within the framework of phonological theory. Signed language phonologists investigate the contrastive form units that combine to create lexical and grammatical units in signed languages (Brentari, 1998, Sandler, 1987). Research on signed languages is recent enough that there is still controversy about the minimal units of the language. However, the first widely known phonological analysis by William Stokoe (Stokoe, 1960, Stokoe et al., 1965) identified a set of phonological parameters that are still core components of phonological descriptions of signed languages: handshape, place of articulation (POA) and movement. Two of these parameters, handshape and POA, were investigated in this study.