The Sensitive Period for Speech Perception
Plasticity for speech perception changes during childhood and adolescence, resulting in a sensitive period for second-language acquisition. However, the developmental time-course and the underlying cognitive and neural mechanisms of this change are not adequately understood. The proposed research investigates the hypothesis that "entrenchment" of native language perception is one mechanism of such age-limited learning. Our specific aims are:
1) Examine the influence of age of arrival on perceptual expertise for second-language speech categories. We will study adult native speakers of Japanese who are learning English using a suite of experimental methods including: a) a visual world task that combines psycho-physical measures and sensitive eye-tracking measures, b) a "task free" dis-habituation paradigm for fMRI to study the functional anatomy of phonetic categorization and c) a dis-habituation paradigm for EEG that matches the time course of the behavioral results and d) productions tasks to assess the relationship between perception and production development.
2) Examine the develop of phonetic categorization in children and adolescents applying the methods developed above to native English speakers age 6-18.
3) Explore the relationship between the emergence of native-language expertise and the decline in plasticity for second-language speech categories in the data from Aims 1 and 2. We hypothesize that the decline in plasticity during the sensitive is associated with increasing perceptual expertise. Data collected with the same paradigms and stimuli for adult native speakers of Japanese, native English speaking children, adolescents and adults will be the basis for a strong test of this hypothesis.