The use of auditory and phonetic memory in vowel discrimination.

A commonly held assumption about memory for speech is that auditory memory is referred to only if phonetic memory does not contain the information needed for a particular trial. However, this assumption is in conflict with recent evidence [Crowder, J. Exp. Psychol.: Learning, Memory, Cognition 8, 153-162 (1982); Repp et al., J. Exp. Psychol.: Human Perception Performance 5, 129-145 (1979)]. The present study provides additional data to help determine how auditory and phonetic memory are used in a vowel discrimination task, and what happens during memory decay. Experiment 1 was conducted to determine whether performance levels decline at similar rates on between- and within-category AX vowel comparison trials when certain methodological problems are removed. This was confirmed. Experiment 2 demonstrated that in the AX task there is a vowel order effect, as Repp et al. found, but that this effect increased across interstimulus delay intervals, in contrast to their findings. The results can be accommodated with a model in which the memory for a vowel is represented as a small, bounded area within the vowel space, and in which memory decay is represented by the expansion of that bounded area over time.