PHASE EFFECTS IN FORWARD MASKING OF THE COMPOUND ACTION-POTENTIAL - ACOMPARISON OF RESPONSES TO STIMULUS AND DISTORTION FREQUENCIES

When a complex stimulus is presented, new frequencies (distortion prod ucts, DPs) are generated within the cochlea. The most intense DPs are lower in frequency than the stimulus tones (primaries). It is not clea r whether the relative phase of stimuli is encoded by neural channels tuned to the primaries or by channels tuned to the DPs. We estimated t he response of auditory nerve fibres tuned to each of these channels a s a function of the relative phase of harmonic stimuli. The compound a ction potential (CAP) evoked by probes at the primary or distortion fr equencies was masked by harmonic 2-tone maskers and cochlear generated DPs. The degree of masking reflected the response to the masker of fi bres tuned to the probe. Changes in relative phase of the primaries re sulted in a large modulation of the response of fibres tuned to the DP s. Except for a primary frequency ratio of 1:2, the response of fibres tuned to the primaries was only shallowly modulated by changes in rel ative phase. However, the level of response to the DPs was much lower than the response to the stimulus tones.