Discriminability, response bias, and phoneme categories in discrimination of voice onset time

Abstract

The ’’phoneme-boundary effect’’ refers to the observation that discrimination of stop consonants across a boundary between phoneme categories is superior to discrimination of comparable stimulus differences within a phoneme category. The present experiment employed signal detection methodology (a) to distinguish between changes in discriminability and response bias; and (b) to reevaluate the role of phonetic categorization in the phoneme-boundary effect. A SAME–DIFFERENT discrimination task compared discrimination of 10− and 20−msec differences in voice onset time (VOT) in a synthetic stimulus continuum ranging from [ba] to [pa] (VOT’s from −50 to +70 msec). Both a clear increase in discriminability and a marked shift in response bias from SAME to DIFFERENT occurred near the voiced–voiceless boundary. When variations in VOT were isolated from syllable context so that they were not categorized as phonemes, discriminability increased near the voiced–voiceless boundary in a manner comparable to the full-syllable stimuli. These data suggest that the phoneme-boundary effect in VOT discrimination reflects a genuine increase in discriminability near the phoneme boundary. However, in agreement with the recent data of J. D. Miller and his colleagues, these results suggest further that the phoneme-boundary effect for VOT is not due exclusively to phonetic categorization but may instead reflect acoustic and auditory properties which are distinct from phonetic processing. Subject Classification: [43]70.30; [43]65.75; [43]70.35..