Discrimination of time intervals bounded by tone bursts

Trained listeners had to discriminate, in a four-level 2AFC paradigm, the duration of a time interval bounded by pairs of brief tone bursts. The time intervals ranged from 10 to 100 msec. When the tone-burst markers were similar in their intensity (86 dB SPL) and frequency (1 kHz), the just noticeable time difference was found to be monotonically related to the base interval. On the other hand, when the intensity of the first marker was severely attenuated (by 50 dB) or when a large (2-octave) difference was introduced between the frequencies of the two markers, the time discrimination functions became nonmonotonic. A similar, albeit slight, departure from monotonicity was also achieved by making the second marker much longer than the first (300 msec vs. 10 msec). The nonmonotonicity of these time discrimination functions is compared to the well-documented nonmonotonicity that may be observed for voice onset time (VOT) discrimination functions.