Structure of phonetic categories produced by general learning mechanisms Free

The development of categories for complex auditory stimuli is an interest for both studies of general category learning and language acquisition. Previous work [Kluender et al., J. Acoust. Soc. Am. 104, 3568–3582 (1998)] demonstrated that avian species can learn to respond differentially to sounds from two vowel categories and the structure of their responses correlate well with human adult ratings of the vowels. In the current study, Japanese quail (Coturnix japonica) were trained to respond to either members of an /i/ or /ε/ distribution and to refrain, in both cases, from responding to members of an /I/ and /æ/ distribution. Birds responding to /ε/ (surrounded by /I/ and /æ/ in the vowel space) showed a prominent peak or ‘‘prototype’’ in their responses. Birds responding to /i/ (extreme in the vowel space) showed a weak or no ‘‘prototype,’’ but showed a strong gradient with response rate increasing for tokens further away from the other vowel distributions in the F1–F2 space. These data demonstrate that internal structure of (phonetic) categories is strongly influenced by relations to the competing stimulus set (vowel space). This is particularly important for theories of categorization or language acquisition that rely heavily on the existence of a ‘‘prototype.’’