New Insights Into Old Puzzles From Infants' Categorical Discrimination of Soundless Phonetic Units

Abstract

For 4 decades, serious scientific debate has persisted as to whether infants' remarkable capacity to detect and categorize phonetic units is derived from language-specific mechanisms or whether this capacity develops out of general perceptual mechanisms. The heart of this controversy has revolved around whether the young human brain is specialized to detect the underlying contrasting patterns in language or whether it simply processes general auditory perceptual features of sound that, over time, become utilized for language learning. This article takes a novel look at this question by using soundless phonetic units from a natural signed language as a new research tool. Research finds that 4-month-old hearing infants categorize soundless phonetic units on the basis of linguistic category membership, whereas 14-month-old infants fail to do so-thereby exhibiting the identical initial capacity and classic developmental shift in infant categorical discrimination of native and nonnative (foreign language) phonetic units in speech. These results suggest a novel testable hypothesis: Infants may begin life with the capacity to detect specific patterned units with alternating contrasts unique to natural language organization and to categorize them on the basis of linguistic category membership.Out of the chaos of sights and sounds in our world, all infants discover the finite set of phonetic units that forms the basis of their specific native language by around 10 months of age. For 4 decades, heated scientific debate has centered on how infants come to have this remarkable capacity. Some have argued that this capacity reflects the neural superiority of the human brain to process specific properties of natural language, whereas others have argued that this capacity is built up from mechanisms of general perception. Here we take a new look at this decadesold puzzle by examining hearing, English-exposed infants' discrimination of nonnative (foreign language) phonetic units that are articulated on the hand in natural signed language. The use of soundless phonetic units allows us to pull apart whether infants have only discrimination for sound, or for language, be it from the mouth or on the hands. The use of two ages (4 and 14 months) that straddle the developmental time when nonnative contrasts in speech are first discriminated and then not discriminated gives us a window into whether the same developmental processes are at work when nonnative phonetic units are on the hands, as well as new insights into the universal nature of these processes in development.

Effects of language experience on the perception of American Sign Language

“…This brings us to the issue of developmental accounts of perceptual learning (Werker, 1994). If categorical perception of handshape contrasts is present from birth, as Baker et al (2006) have argued, and is subsequently lost by 14 months of age in individuals without exposure to sign, then we should find low levels of discrimination performance on both within- and between-category contrasts for deaf non-native and hearing L2 signers. By this account, the native signers should distinguish themselves as the only group with unusually good discrimination at identification boundaries.…”

“…These studies contradict the first investigation of categorical perception in ASL, in which Supalla & Newport (1975, as reported in Newport, 1982) found no evidence of categorical perception of either handshape or POA by native signers. Subsequently, Baker, Golinkof & Petitto (2006) tested discrimination of one handshape contrast by 4-month-old and 14-month old hearing infants with no prior sign exposure, and found that only the younger of these two groups discriminated the handshape contrast. These authors draw a parallel between studies showing sensitivity to spoken language contrasts in infancy that are subsequently lost in speakers without exposure to those contrasts, such as loss of sensitivity to the retroflex /T/-/t/ distinction by English speakers (cf.…”

The perception of handshapes in American Sign Language

“…Second, there is behavioral evidence from Baker, Golinkoff, and Petitto (2005) that 4-monthold hearing (speech-exposed) infants, who have no exposure to a signed language, can categorically discriminate phonetic handshape units in ASL. The infants also have no relevant experience with the handshape contrasts, which were a subset of the stimuli used in the present study, and thus cannot be using category labels for discrimination.…”

Phonological reduplication in sign language: Rules rule

“…As in spoken phonology, signed phonological systems encode the hierarchical organization of discrete distinctive features (Brentari, 1998; Sandler and Lillo-Martin, 2006), they represent the syllable—a prosodic unit that is demonstrably distinct from a morpheme (Brentari, 1998; Sandler and Lillo-Martin, 2006), and constrain their sonority profile (Stokoe, 1960; Klima and Bellugi, 1979; Corina, 1990; Perlmutter, 1992; Brentari, 1993, 1994, 1998; Corina and Sandler, 1993; Brentari, 2006; Sandler and Lillo-Martin, 2006; Sandler, 2008; Jantunen and Takkinen, 2010; Wilbur, 2012). Experimental research on sign languages has further shown that signers—both adults (Lane et al, 1976; Newport, 1982; Hildebrandt and Corina, 2002; Emmorey et al, 2003; Baker et al, 2005; Best et al, 2010) and infants (Baker et al, 2006; Palmer et al, 2012)—encode phonological features as phonetic categories, subject to perceptual narrowing in the first year of life (Baker et al, 2006; Palmer et al, 2012). Moreover, distinct feature classes differ in their contribution to language processing.…”