Average‐rate, fundamental and harmonic‐distortion components of responses of cochlear nerve fibers to single‐frequency tone bursts: Comparison with an exponential model

Abstract

The effects of stimulus envelope on the response characteristics of cochlear nerve fibers can be studied with a class of stimuli of the form p(t) = ex(t) sin (ωt). In this study, the modulating function eg(t) was chosen to produce a train of tone bursts of specified duty cycle and rise/fall times. The technique of Fourier analysis of period histograms described by Kim et al. (preceding abstract) has been extended to handle variations in response components R0,R1, and θ1 as a function of time both within and between each tone burst in a train of bursts. Using tone bursts of 320 ms duration and 20 ms rise/fall times with a duty cycle of 21% we have observed that, during the course of a tone burst: (1) both R0 and R1 rapidly reach a peak value and then decline over the following 50–100 ms to quasi‐steady—state values; (2) the time courses of R0 and R1 during a tone burst are almost identical in shape, i.e., the ratio, R1/R0, reaches its maximum value rapidly and remains constant throughout the duration of a tone burst despite noticeable fluctuations in R1 and R0; (3) the fundamental phase θ1, is constant throughout the total duration of a tone burst; (4) R1R0 saturates at lower sound pressure levels (SPL) than either R0 or R1; (5) the shapes of R0 and R1 vs SPL curves change substantially and progressively for successive periods during the onset portion of the response; and (6) in some cases, the R0 and R1 versus SPL curves for individual periods during the first 12–20 ms following tone burst onset show pronounced nonmonotonic behavior with maxima occurring at as low as 50 dB re 20 μN/m2.