Formation of categories for complex novel auditory stimuli

Abstract

Categorization of complex sounds with multiple, imperfectly valid cues is fundamental to phonetic perception. To study the general perceptual and cognitive processes that support complex sound categories, a novel stimulus set was created that allows tight control of category structure and input distributions. Stimuli were created from 300-ms noise bursts by applying bandstop filters at varying center frequencies and manipulating rise/fall time of stimulus onset and offset. Stimuli were assigned to one of two categories and presented to participants in a category identification and an AX discrimination task. Feedback was provided during identification trials, but not during discrimination tasks. Participants quickly learned to apply the category labels with high accuracy. Identification reaction times followed a pattern typical of speech stimuli with an apex in reaction time at category boundary. These results are consistent with formation of new auditory categories. Preliminary results indicate that discrimination performance is not tightly coupled with development of sharp identification functions and response-time peaks at category boundaries. Implications for mechanisms of speech categorization and category formation will be discussed. [Work supported by CNBC, NIH, and NSF.]