A study of the phonetic detail used in lexical tasks during infancy

In speech perception tasks young infants show remarkable sensitivity to fine phonetic detail. Despite this impressive ability demonstrated at early ages, studies of word learning in young toddlers indicate that they have difficulty learning similar-sounding words. This evidence suggests that infants may not be using this speech-perception ability as they begin to learn words. The studies in this thesis were designed to test how infants' speech-perception skills are used in the early stages of word learning. Using a simple habituation procedure, we have shown in earlier work that 14-month-old infants, but not younger infants, are able to learn the association between novel nonsense words and objects (Werker, Cohen, Lloyd, Casasola, & Stager, 1998). The current series of experiments used this simple habituation procedure to test whether infants use minimally contrastive phonetic detail in the very early stages of word learning. In this thesis, I show that 14-month-old infants, who are on the cusp of word learning, while still able to discriminate phonetically-similar words in a speech perception task, do not incorporate minimally contrastive phonetic detail when first forming word-object associations. Infants of 8 months of age do, however, appear to use fine phonetic detail in a similar task. Taken together, these results suggest a decline in the phonetic detail used by infants as they move from processing speech to learning words. I hypothesize that this decline may occur as infants move from treating the task as one of speech perception to treating the task as one of word learning.Arts, Faculty ofPsychology, Department ofGraduat