Temporal resolution is an important factor in auditory processing, especially in speech recognition. A psychoacoustic gap detection test has been divised to evaluate it in humans.
We designed an electrophysiological gap test using electrocochleograms (ECochGs) and auditory evoked brainstem responses (ABRs) to clarify the region in which the gap detection threshold is decided in the auditory pathway. ECochGs and ABRs were elicited simultaneously by a probe tone (4kHz, 85 dBSPL, 2msec duration, tone burst) with a preceding masker tone (4kHz, 85dBSPL, 50 msec duration, tone burst) in 16 subjects with normal hearing. As two tone intervals (gaps) were shortened from 10 msec by 2 msec steps, the amplitudes of the action potential (AP) in ECochGs and wave V in ABRs decreased and became undetectable. The thresholds for AP detection which are regarded as gap detection thresholds in the cochlea ranged from 2 to 6 msec with an average of 4.0 msec, while the thresholds for wave V detection, thresholds in the inferior colliculus, had the same range with an average of 4.4 msec, which is similar to the results of the psychoacoustic gap test introduced by Shailer and Moore in 1989. We conclude that a gap detection threshold is present in the peripheral auditory system in normal listeners.
