Identification and discrimination of the relative onset time of two component tones: Implications for voicing perception in stops

Experiments on the voiced–voiceless distinction in stop consonants have shown sharp and consistent labeling functions and categorical-like discrimination functions for synthetically produced speech stimuli differing in voice-onset time (VOT). Other research has found somewhat comparable results for young infants and chinchillas as well as cross-language differences in the perception of these same synthetic stimuli. In the present paper, four experiments were carried out to investigate a possible underlying basis of these seemingly diverse results. All of the experiments employed a set of nonspeech tonal stimuli that differed in the relative onset time of their components. In the first experiment identification and discrimination functions were obtained with these signals which showed strong evidence for categorical perception: the labeling functions were sharp and consistent, the discrimination functions showed peaks and troughs which were correlated with the labeling probabilities. Other experiments provided evidence foir the presence of three distinct categories along this nonspeech stimulus continuum which were separated by narrow regions of high discriminability. Based on these findings a general account of voicing perception for stops in initial position is proposed in terms of the discriminability of differences in the temporal order of the component events at onset.