The perception of handshapes in American Sign Language

Abstract

Despite the constantly varying stream of sensory information that surrounds us, we humans can discern the small building blocks of words that constitute language (phonetic forms) and perceive them categorically (categorical perception, CP). Decades of controversy have prevailed regarding what is at the heart of CP, with many arguing that it is due to domain-general perceptual processing and others that it is determined by the existence of domain-specific linguistic processing. What is most key: perceptual or linguistic patterns? Here, we study whether CP occurs with soundless handshapes that are nonetheless phonetic in American Sign Language (ASL), in signers and nonsigners. Using innovative methods and analyses of identification and, crucially, discrimination tasks, we found that both groups separated the soundless handshapes into two classes perceptually but that only the ASL signers exhibited linguistic CP. These findings suggest that CP of linguistic stimuli is based on linguistic categorization, rather than on purely perceptual categorization.How do we discern the phonetic units that make up the constantly varying linguistic stream around us? One of the most researched answers to this question has been surrounded by controversy since the 1950s, when human adults were found to partition speech sounds from a continuum into discrete categories, a phenomenon known as categorical perception (CP; see Liberman, 1996, for a review). Early findings regarding the CP of speech sounds suggested that CP is specific to spoken language in humans and is the result of linguistic-specific processing. This special mechanisms hypothesis was supported by findings from two lines of research, the first of which was that CP occurred only for contrasts that were phonemic in a speaker's native language. For example, it has been shown that adult speakers of Japanese have difficulty distinguishing between /l/ and /r/ (Miyawaki et al., 1975), and Werker, Gilbert, Humphrey, and Tees (1981) and Werker and Tees (1983) have also shown that Englishspeaking adults cannot discriminate the Hindi contrasts /t h a/-/d h a/ (voiceless aspirated dental stop vs. breathy voiced) or /t'a/-/ta/ (voiceless unaspirated retroflex vs. dental) as well as Hindi adults can.An earlier finding came from Eimas, Siqueland, Jusczyk, and Vigorito's (1971) work on 1-month-old infants' speech perception. They showed that infants could discriminate computergenerated sounds that straddled the adult phonetic boundary but failed to discriminate stimuli NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript that were from within the same adult phonetic category. The infants' ability to do this without having had a long period of experience in listening to or producing speech suggested that CP was not learned and was, in fact, a part of the biological makeup of the human species. In addition, it has been well documented in the literature that infants can easily discriminate both native and nonnative oral consonant contrasts without having had r...

Perceptual categorization of handling handshapes in British Sign Language

“…The outcome of the handshape identification task was consistent with earlier studies which found a similar sigmoidal function in deaf ASL signers and hearing non-signers (Baker, et al, 2005;Lane, Boyes-Braem, & Bellugi, 1976). In line with previous results, our findings suggest that linguistic experience does not mediate identification of visual features for the purpose of binary handshape categorization.…”

“…The increased discrimination accuracy for handshapes straddling category boundaries has previously been attributed to the perceived contrast between phoneme categories in speech (Liberman, et al, 1957;Liberman, et al, 1961) or in lexical signs in ASL (Baker, et al, 2005;Emmorey & Herzig, 2003). Baker et al (2005) …”

“…The current findings suggest that direct comparisons between perception of handshapes in lexical signs , Baker et al, 2005 and less lexicalized handling constructions needs to be made with caution. In less lexicalized and less conventionalized constructions, greater variation of form is permitted and subtle changes in form are more noticeable because of the semantic values associated with each handshape token.…”

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

“…The fourth study (Baker, Idsardi, Golinkoff, & Petitto, 2005) differed importantly from the other three in its use of nonsense stimuli rather than real signs; it also differed from Emmorey et al (2003) and the follow-up experiments of Newport (1982) by using dynamic video stimuli. Baker et al employed three handshape contrasts (A-vs. B-bar, as in Emmorey et al, 2003, as well as 5 vs. flat-O and 5 vs. S; see Figure 2A).…”

“…Also, comparison of native versus nonnative lateonset deaf signers allowed assessment of ASL onset-age effects with hearing status held constant. 1 Given that both speech and signs have phonological structure, one hypothesis is that native phonological structure will affect perception of contrasts similarly by users Sign-naive participants allegedly lack categorical perception for all sign contrasts tested (dynamic, Baker et al, 2005;static, Emmorey et al, 2003).…”