Forward masking of auditory nerve (N1) and brainstem (wave V) responses in humans

Wave V of the auditory brainstem response and N1 from the ear canal were recorded from normal hearing adults using a forward masking paradigm. Response amplitudes and latencies to 40 dB HL probe clicks presented in quiet and as a function of the time delay (delta T) following short-duration wideband noise maskers were measured. The masking effects for wave V were different than for N1. The primary effects were decreases in N1 amplitude and increases in wave V latency, neither of which were recovered by delta T = 100 ms. The V-N1 latency interval increased for delta Ts below 50 ms. Wave V amplitude was fully recovered by delta T = 25 ms, even though N1 amplitude was significantly reduced. Recovery functions are also described for some variations in masker duration and masker level. Results are explainable in terms of peripheral and central processes or entirely peripheral processes. The differential effects of N1 and wave V suggest, at least for some stimulus conditions, that these two responses are to some degree independent of each other.