Compound action potential measures of frequency selectivity.

In this paper we demonstrate that it is possible to obtain a measure of the frequency selectivity of the ear by means of forward masking of the whole nerve action potential (AP). The AP frequency tuning curves resulting from the forward masking measurements appeared to be similar to single fiber tuning curves. The masker preceding the test tone produced a slow off-response which we suppose to be super-imposed on the AP provoked by a test tone. High and low-pass filtering of the test tone with slopes up to 96 dB/oct improved tuning. Steeper slopes gave no noticeable improvement. Filtered test tones produced AP tuning curves which were wide in comparison with single fiber tuning curves. Moreover, AP tuning curves become even wider at high test tone levels. In spite of this road tuning, changes in frequency selectivity of the ear, caused by noise trauma, are reflected in the AP tuning curve.