The medial olivocochlear reflex has been hypothesized to improve the detection and discrimination of dynamic signals in noisy backgrounds. This hypothesis was tested here by comparing behavioral outcomes with otoacoustic emissions. The effects of a precursor on amplitude-modulation (AM) detection were measured for a 1-and 6-kHz carrier at levels of 40, 60, and 80 dB SPL in a two-octave-wide noise masker with a level designed to produce poor, but above-chance, performance. Three types of precursor were used: a two-octave noise band, an inharmonic complex tone, and a pure tone. Precursors had the same overall level as the simultaneous noise masker that immediately followed the precursor. The noise precursor produced a large improvement in AM detection for both carrier frequencies and at all three levels. The complex tone produced a similarly large improvement in AM detection at the highest level but had a smaller effect for the two lower carrier levels. The tonal precursor did not significantly affect AM detection in noise. Comparisons of behavioral thresholds and medial olivocochlear efferent effects on stimulus frequency otoacoustic emissions measured with similar stimuli did not support the hypothesis that efferent-based reduction of cochlear responses contributes to the precursor effects on AM detection.

Behavioral measures of amplitude modulation (AM) detection and envelope interaural-phase-difference (eIPD) detection reflect listeners’ ability to process temporal information. Robust encoding of temporal envelopes is necessary for understanding speech in a complex acoustic environment and for spatial segregation of a target speech from interfering background. It has been suggested that a large variability in performance in psychophysical tasks involving temporal envelope processing and in spatial release from masking for speech intelligibility may arise from cochlear synaptopathy. However, many studies have not found significant correlations between these measures and the amount of self-reported noise exposure in young listeners with audiometrically normal hearing. Similarly, electroencephalographic envelope-following responses did not significantly correlate with noise exposure or with behavioral performance reliant on envelope processing young normal-hearing population. In this study, behavioral measures in psychophysical tasks (AM and eIPD detection) and speech intelligibility in two-talker babble were measured for listeners with normal and near-normal hearing across a wide age range (20 to 69 years). Correlational analyses were performed using behavioral measures and envelope-following responses collected from the same listeners. Results will be discussed in terms of sensitivity of these measures to effects of aging and high-frequency hearing loss. [Work supported by NIH Grant R01 DC015987.]