Towards a computational account of how infants build a semantic system: Lexical-Semantic and Phonological Priming in Early Lexical Development

Several decades of research documents that infants as young as 12-months-old understand the meaning of many dozens of words insofar as they are able identify an appropriate referent for a word when give a choice between alternatives. The ability to identify appropriate referents, given a label, develops rapidly during the second year of life, so that by the time an infant reaches her second birthday she may understand many hundreds of words. Although we know a great deal about the types of words that infants understand and produce during their second year so-called word-world relationships, surprisingly, we know virtually nothing about their appreciation of the meaning relationships between words themselves. These meaning relations lie at the heart of the human semantic system: Part of knowing what the word dog means involves knowing, if only implicitly, how it relates to the meaning of cat or bone . A proper understanding of semantic development involves identification of how and when infants begin to link words together in a network of meanings, thereby going beyond word-world associations to achieve a system of meanings that underpins human communication.

The investigation of the structure of the mental lexicon in adults has relied heavily on priming studies: Words which prime each other do so because they are linked together in the lexicon. We adopt a similar strategy for investigating the structure of the infant lexicon using an adaptation of the inter-modal preferential looking task in which levels of lexical activation are indexed by visual preference for a target over a distracter object under linguistically primed versus unprimed conditions. The results of our studies indicate that robust semantic/associative and phonological priming is in place by 21 24 months-old whereas 18-month-olds fail to show clear cut sensitivity to priming. Additional control experiments have revealed that the locus of these priming effects are at the lexical-semantic level, indicating that before infants reach their second birthday they have already started to form semantic/associative links between words in a fashion that begins to resemble the structure of the adult lexicon. The implications of these findings for a computational account of early lexical development are explored.