Between-frequency and between-ear gap detections and their relation to perception of stop consonants

The objective of this study was to examine the hypothesis that between-channel gap detection, which includes between-frequency and between-ear gap detection, and perception of stop consonants, which is mediated by the length of voice-onset time (VOT), share common mechanisms, namely relative-timing operation in monitoring separate perceptual channels. Design: The authors measured gap detection thresholds and identification functions of/ba/and/pa/along VOT in 49 native young adult Japanese listeners. There were three gap detection tasks. In the between-frequency task, the leading and trailing markers differed in terms of center frequency (F_c). The leading marker was a broadband noise of 10 to 20,000 Hz. The trailing marker was a 0.5-octave band-passed noise of 1000-, 2000-, 4000-, or 8000-Hz F_c. In the between-ear task, the two markers were spectrally identical but presented to separate ears. In the within-frequency task, the two spectrally identical markers were presented to the same ear. The/ba/-/pa/identification functions were obtained in a task in which the listeners were presented synthesized speech stimuli of varying VOTs from 10 to 46 msec and asked to identify them as/ba/or/pa/. Results: The between-ear gap thresholds were significantly positively correlated with the between-frequency gap thresholds (except those obtained with the trailing marker of 4000-Hz F_c). The between-ear gap thresholds were not significantly correlated with the within-frequency gap thresholds, which were significantly correlated with all the between-frequency gap thresholds. The VOT boundaries and slopes of/ba/-/pa/identification functions were not significantly correlated with any of these gap thresholds. Conclusions: There was a close relation between the between-ear and between-frequency gap detection, supporting the view that these two types of gap detection share common mechanisms of between-channel gap detection. However, there was no evidence for a relation between the perception of stop consonants and the between-frequency/ear gap detection in native Japanese speakers.