Abstract:
Frequency discrimination with 40-ms continuous signals was compared to that for signals consisting of two 20-ms tone bursts separated by a 40-ms gap. Performance was impaired for gap signals at the test frequency of 250 Hz but not at frequencies above 1000 Hz. Studies at 250 Hz showed that, by reference to a 40-ms continuous signal, subjects performed poorly with stimuli consisting of two 20-ms bursts, however short the gap duration. A possible explanation within a place mechanism framework is that the bandwidth of the 20-ms bursts limits the sharpness of the excitation pattern at low frequencies. However, there is strong evidence for the use of a timing mechanism at low frequencies [A. Sek and B. C. J. Moore, J. Acoust. Soc. Am. 97, 2479--2486 (1995)]. The results can be interpreted in terms of a timing mechanism that operates on the interspike intervals derived from phase locking in the auditory nerve. The mechanism has a long integration period that can be reset by discontinuities in the ongoing signal. [Work supported by MRC (UK).]