AP measurements of short-term adaptation in normal and in acoustically traumatized ears

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Abstract
A forward-masking paradigm was used to measure short-term adaptation in normal and in acoustically traumatized ears. AP amplitude was measured to a tone burst of fixed frequency and level while masker intensity (Lm) and duration (Tm), as well as the interval between masker offset and probe onset (Δt) were varied. Masker and probe frequency were held constant at 4 kHz. In one experiment, short-term perstimulatory adaptation was examined through the measurement of probe-elicited N1 amplitude at a fixed Δt while both Lm and Tm were varied. These probe response-versus-Tm functions were modeled exponentially, yielding time constants that did not differ between normal and exposed ears. In another series of experiments, recovery from short-term adaptation was examined by holding Tm constant and measuring probe-response amplitude as a function of Δt. When the decrement- (amount by which the probe-elicited N1 amplitude was reduced by the masker) versus-Δt functions were fit with an exponential model that accounted for long-term effects, no differences were observed between recovery time constants from normal and traumatized ears. Finally, growth of response to the masker was estimated by examining the decrement in normalized amplitude of response to the probe as a function of Lm. Acoustically traumatized ears revealed steeper growth functions, suggesting steeper single-fiber rate-versus-level functions.

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