Auditory and phonetic category formation

Among infants' first steps in language acquisition is learning the relevant contrasts of the language-specific phonemic repertoire. This learning is viewed as the formation of categories in a multidimensional psychophysical space. Research in the visual modality has shown that for adults, some kinds of multidimensional categories are very difficult to learn without supervision. The success of infants in acquiring a phonetic system suggests that formation of multidimensional categories might be more tractable in the auditory modality. We describe experiments investigating adult learning of multidimensional speech and nonspeech categories. These experiments revealed that learners’ degree of difficulty is actually significantly greater than that observed in the visual modality. Despite comparable methods, our results differ from those in visual category learning: feedback that is effective for visual categories is not as effective in the auditory modality. Attending to more than one dimension in auditory category formation is possible for adult listeners, but it is very hard.