Onset responses in single auditory-nerve fibers

Abstract

The maximum response at the onset of a CF tone burst was obtained as a function of sound intensity level and prior adaptation. A stimulus rise time of 1 ms was used to maximize the onset response as well as to produce a simultaneously recorded whole-nerve action potential (AP). As intensity increased, the onset response increased and in some units reached a maximum value of 1 spike per stimulus presentation within a 1-ms interval. The absolute refractory period of the fiber prevented a further increase in the number of spikes. Nevertheless, further increases in intensity affected the onset response by reducing the latency to the onset spike and the variability in its time of occurrence. Consequently, the maximum response in spikes per second continued to increase when it was measured using a sufficiently small time interval, e.g., 55 μs. Prior adaptation reduced the magnitude and increased the latency and variability of the onset response. These effects could account for some of the concurrent changes in the AP.