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The taxonomic assumption, or noun-category bias, is thought to facilitate word learning by focusing children's attention on taxonomic categories as likely candidates for word meanings. Three experiments were conducted to disentangle the role of taxonomic relations and shape similarity in 18- and 24-month-olds' responses on a noun category bias task. The relationship between vocabulary composition and performance on these tasks was also examined. Results indicated that both 18- and 24-month-old children were predominantly guided by shape similarity when extending novel labels. However, some evidence that taxonomic information can be used to guide word extension was found in the 24-month-old group. Those children with a larger proportion of nouns in their vocabulary were more likely to use information about category membership when extending words, even in the absence of shape similarity.
The challenge that a young child faces when learning a new word is illustrated clearly by Quine's (1960) `problem of radical translation'. According to Quine, when a word is uttered, its referent is ambiguous. Consider Quine's example of an anthropologist visiting a radically different culture on Earth. He observes a speaker utter 'gavagai' as a rabbit runs by and faces the dilemma of assigning the correct meaning to the utterance. In this context, 'gavagai' could have countless referents, including 'fast', 'running', 'rabbit', 'tail' etc. Similarly, young children encounter the formidable task of identifying the specific referent for words produced in their environment. Yet, despite the apparent complexity of this task, children learn language at a remarkably rapid pace, acquiring an average of six words a day between the ages of 2 and 6 years (Nelson, 1973).
In view of their rapid and seemingly effortless acquisition of vocabulary, several researchers have argued that young children must possess word learning constraints or biases that guide their assignments of word meanings (e.g. Golinkoff, Mervis & HirshPasek, 1994; Markman, 1989, 1992; Mervis & Bertrand, 1993). That is, children are thought to be predisposed to entertain certain hypotheses about word meaning over others. One word learning bias that has received a great deal of empirical scrutiny in recent years is the taxonomic assumption or noun category bias (Markman, 1989; Waxman & Hall, 1993). According to this bias, children assume that a novel word refers to members of the same...