Perception of voice-onset-time continua: a signal detection analysis

An absolute identification task and various discrimination tasks were performed on synthetic syllables initiated by alveolar stops varying in voice-onset-time (VOT). Signal detection analyses of the data yielded three main findings. First, discrimination d's exceeded those for absolute identification. Greater instability of judgment in the latter than in the former task explained this difference. Second, stimuli within a phonetic category were discriminable, even in a delayed 2IAX paradigm with 4s between stimuli. Third, a category boundary effect appeared: identification and discrimination d's were largest around the voiced/voiceless boundary for alveolar stops. The relationship between discrimination and identification d's varies with response constraints, the number of just noticeable differences in the stimulus array, and stability of judgments in the various tasks. Nearly equal performance in discrimination and identification tasks is not a sufficient condition for a category boundary effect to occur. Several arguments are advanced against a dual-coding model. A continuous model which invokes only a single decision process may account more gracefully for the relationship between identification and discrimination of both consonants and vowels.