Latency and amplitude compound action potential tuning curves for tonal stimuli with nontraditional envelopes

To evaluate the influence of the acoustic context on the latency and amplitude tuning curves (TCs) of cochlear nerve compound action potentials (CAPs), tonal stimuli were generated with a variety of amplitude modulation envelopes. CAPs were produced by intensity increases (onsets) and decreases (offsets) from the low ambient sound level and by intensity changes from a preexisting tonal level. Onset CAPs from ambient levels generated V-shaped TCs. However, when simultaneous masking was used with onset CAPs which were produced by a 5- to 12-dB increase from preexisting levels of approximately 65 dB SPL, TCs were W-shaped and similar in appearance to those produced by simultaneous masking of offset CAPs. The forward masking of this same CAP resulted in a very sharp V-shaped TC. These data suggest that the preadaptation to 10 ms of a moderate level of a tonal stimulus can increase the tuning of ensembles of cochlear neurons to subsequent transient amplitude changes.