Temporal aspects of suppression in distortion-product otoacoustic emissions

This study examined the time course of cochlear suppression using a tone-burst suppressor to measure decrement of distortion-product otoacoustic emissions (DPOAEs). Seven normal-hearing subjects with ages ranging from 19 to 28 yr participated in the study. Each subject had audiometric thresholds ≤ 15 dB HL [re ANSI (2004) Specifications for Audiometers] for standard octave and inter-octave frequencies from 0.25 to 8 kHz. DPOAEs were elicited by primary tones with f(2) = 4.0 kHz and f(1) = 3.333 kHz (f(2)/f(1) = 1.2). For the f(2), L(2) combination, suppression was measured for three suppressor frequencies: One suppressor below f(2) (3.834 kHz) and two above f(2) (4.166 and 4.282 kHz) at three levels (55, 60, and 65 dB SPL). DPOAE decrement as a function of L(3) for the tone-burst suppressor was similar to decrements obtained with longer duration suppressors. Onset- and setoff- latencies were ≤ 4 ms, in agreement with previous physiological findings in auditory-nerve fiber studies that suggest suppression results from a nearly instantaneous compression of the waveform. Persistence of suppression was absent for the below-frequency suppressor (f(3) = 3.834 kHz) and was ≤ 3 ms for the two above-frequency suppressors (f(3) = 4.166 and 4.282 kHz).