Threshold-duration functions of chinchilla auditory nerve fibers

The purpose of the present study was to measure the change in threshold as a function of stimulus duration in single auditory nerve fibers. Thresholds were measured at each neuron's characteristic frequency (CF) for eight stimulus durations ranging from 8 to 1024 ms. Using an adaptive, two- interval, forced-choice threshold-tracking procedure with a 2-down, 1-up rule, thresholds were estimated based on a decision criterion of one spike or greater difference between tone and no-tone intervals. The results showed that mean thresholds decreased with increasing stimulus duration by approximately 14.6 dB over the range of durations tested. Analysis of group and individual data showed that thresholds decreased by approximately 6-7 dB per decade of duration. The slope of threshold improvement decreased systematically with increasing CF, consistent with previous physiological and psychophysical data.