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

Abstract

Signal detection methodology was employed in human subjects to distinguish between changes in discriminability and response bias and to reevaluate the role of phonetic categorization in the pheneme-boundary effect. A SAME-DIFFERENT discrimination task compared discrimination of 10 and 20 ms differences in voice onset time (VOT) in a synthetic stimulus continuum ranging from [ba] to [pa] (VOT''s from -50 to +70 ms). 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. The phoneme-boundary effect in VOT discrimination apparently reflects a genuine increase in discriminability near the phoneme boundary. The phoneme-boundary effect for VOT is probably not due exclusively to phonetic categorization but may instead reflect acoustic and auditory properties which are distinct from phonetic processing.