Synthetic steady‐state vowels from an /i/‐/I/‐/ / continuum were presented in an AX discrimination task. The interval between the stimuli in a pair was either short (240 ms) or long (1920 ms), and either empty or filled with irrelevant vowel sounds. Discrimination performance was disturbed by both these manipulations, suggesting that auditory memory is subject to decay as well as to interference. In a second experiment, we predicted discrimination performance at short‐unfilled and long‐filled intervals from identification response to the same AX pairs. While obtained discrimination performance exceeded the predictions, this difference was equally small at the two interstimulus intervals. Identification was as much affected by interstimulus interval as discrimination: There were large contrast effects at the short‐unfilled interval, but not at the long‐filled interval. Implications of these results for models of categorical perception will be discussed. [Work supported by NICHD.]