Acquiring Word Learning Biases

Acquiring Word Learning Biases Zi L. Sim (zilin@berkeley.edu) Sylvia Yuan (shyuan@berkeley.edu) Fei Xu (fei_xu@berkeley.edu) Department of Psychology, University of California, Berkeley Berkeley, CA 94720 USA Abstract Previous research has shown that infants can acquire a “shape bias” in word learning when presented with labels that are perfectly correlated with object shape. However, little research examines whether children can acquire a non-shape word learning bias. Research on inducing this bias can help inform the origins of the shape bias. In our experiment, 3 year-old children successfully acquired a new bias even with relatively few objects and a short training session, illustrating the relevance of the overhypothesis formation account in explaining the acquisition of early inductive constraints. Keywords: shape bias; overhypothesis; word learning; inductive constraints Introduction How does a child, learning his/her first language, map words to their referents? According to Quine (1960), a young child learning his first language, is similar to a traveler in a new place without any knowledge of the local language. When a native speaker says “Gavagai! ”, there is an infinite number of referents for the word, such as whole objects, parts of objects, or properties of objects. How does the traveler, or the child, then map the word “gavagai” to the correct referent? Early word learning is thus an inductive problem, where the young child attempts to make inferences about words and their referents. Children appear to be remarkably proficient at solving such problems of induction. They circumvent the mapping problem, and quickly map the words they hear to the correct object category (Bloom, 2000; Markman, 1989; Carey & Bartlett, 1978). The apparent ease at which young children learn suggests that their learning is supported by strong inductive constraints (Markman, 1989). In the domain of word learning, a possible inductive constraint is the shape bias (Landau, Smith & Jones, 1988), the tendency for children to extend new object names on the basis of shape similarity. This shape bias has been demonstrated in various studies (e.g. Landau et al., 1988; Soja, Carey & Spelke, 1991; Samuelson, 2002) and has also been consistently linked with an increased rate of noun acquisition in children (e.g. Smith, Jones, Landau, Gershkoff-Stowe & Samuelson, 2002), suggesting that this particular bias may aid children in mapping new words to their referents quickly. How does the shape bias emerge? While one would be hard-pressed to find a truly nativist account of the shape bias, some might still argue that the shape bias is an innate constraint that a child is born with, especially because it emerges early in development. The nativist account posits that children are biased to pay attention to shape of objects, and to generalize labels according to shape. However, such a nativist account neither addresses how the shape bias came to be an innate constraint, nor the processes and mechanisms behind the bias (Xu, Dewar & Perfors, 2009). Furthermore, children do not approach word learning with an expectation that extension of labels is solely guided by shape similarity. For example, children consider the taxonomic categories (Cimpian & Markman, 2005) and the solidity (Soja et al., 1991) of objects. Hence, a nativist account of the shape bias is one that is difficult to defend. While a nativist account of the shape bias has been widely rejected, other theories fall on a continuum between the constraint being innate, and the constraint being learnt. The “shape-as-cue” account, for example, (Bloom, 2000; Markson, Diesendruck & Bloom, 2008) falls at the center of such a continuum. The proponents of the “shape-as-cue” account argue that children organize objects by shape because shape serves as a reliable cue to object kinds. In this account, a shape bias emerges from two different understandings: first, children understand that count nouns refer to object categories (Dewar & Xu, 2007) and second, they perceive shape to be a reliable and available cue to object category membership. Consequently, on this account, the perceptual dimension of shape is not special – when other cues such as texture or function are more reliable cues for object category membership, children use them in their extension of novel names (Booth & Waxman, 2002; Ware & Booth, 2010), and a shape bias will not emerge. However, the shape-as-cue account leaves the origins of the shape bias unaddressed. For example, how do children come to believe that shape is a reliable cue of object category membership? We investigate this question in the current study, by asking whether children can acquire a different bias when given the relevant input. Another account, the Attentional Learning Account (ALA) proposed by Smith and her colleagues (Smith et al., 2002), addresses the origins of the shape bias more fully, by positing that the bias is a learnt constraint. According to ALA, the development of word learning biases is supported by connectionist networks, which allow children to learn from the many “correlations among linguistic devices, object properties, and perceptual category organization” (Colunga & Smith, 2005) in their learning environment.