The experiments presented in this paper explore the hypothesis that cochlear gain is reduced, in a frequency-specific manner, over the course of a sound ͑called a "precursor"͒ which was designed to activate the medial olivo-cochlear reflex ͑MOCR͒. Psychophysical tuning curves ͑PTCs͒ and off-frequency growth of masking ͑GOM͒ functions were measured with two precursors. The on-frequency precursor condition, which was hypothesized to activate the MOCR at the signal frequency, produced a PTC with a lower best frequency in all subjects consistent with less gain. This same condition produced a GOM function with less gain and an elevated compression breakpoint. The data were analyzed with two models. The gain-reduction model, which assumed a change in the basilar membrane input-output function, was superior at predicting the data relative to a model of additivity of masking.

Musicianship confers enhancements to hearing at nearly all levels of the auditory system from periphery to percept. Musicians' superior psychophysical abilities are particularly evident in spectral discrimination and noise-degraded listening tasks, achieving higher perceptual sensitivity than their nonmusician peers. Greater spectral acuity implies that musicianship may increase auditory filter selectivity. This hypothesis was directly tested by measuring both forward- and simultaneous-masked psychophysical tuning curves. Sharper filter tuning (i.e., higher Q10) was observed in musicians compared to nonmusicians. Findings suggest musicians' pervasive listening benefits may be facilitated, in part, by superior spectral processing/decomposition as early as the auditory periphery.

Frequency selectivity was evaluated under two conditions designed to assess the influence of a "precursor" stimulus on auditory filter bandwidths. The standard condition consisted of a short masker, immediately followed by a short signal. The precursor condition was identical except a 100-ms sinusoid at the signal frequency (i.e., the precursor) was presented before the masker. The standard and precursor conditions were compared for measurements of psychophysical tuning curves (PTCs), and notched noise tuning characteristics. Estimates of frequency selectivity were significantly broader in the precursor condition. In the second experiment, PTCs in the standard and precursor conditions were simulated to evaluate the influence of the precursor on PTC bandwidth. The model was designed to account for the influence of additivity of masking between the masker and precursor. Model simulations were able to qualitatively account for the perceptual data when outer hair cell gain of the model was reduced in the precursor condition. These findings suggest that the precursor may have reduced cochlear gain, in addition to producing additivity of masking. This reduction in gain may be mediated by the medial olivocochlear reflex.

Masked detection threshold for a short tone in noise improves as the tone's onset is delayed from the masker's onset. This improvement, known as "overshoot," is maximal at mid-masker levels and is reduced by temporary and permanent cochlear hearing loss. Computational modeling was used in the present study to evaluate proposed physiological mechanisms of overshoot, including classic firing rate adaptation and medial olivocochlear (MOC) feedback, for both normal hearing and cochlear hearing loss conditions. These theories were tested using an established model of the auditory periphery and signal detection theory techniques. The influence of several analysis variables on predicted tone-pip detection in broadband noise was evaluated, including: auditory nerve fiber spontaneousrate (SR) pooling, range of characteristic frequencies, number of synapses per characteristic frequency, analysis window duration, and detection rule. The results revealed that overshoot similar to perceptual data in terms of both magnitude and level dependence could be predicted when the effects of MOC efferent feedback were included in the auditory nerve model. Conversely, simulations without MOC feedback effects never produced overshoot despite the model's ability to account for classic firing rate adaptation and dynamic range adaptation in auditory nerve responses. Cochlear hearing loss was predicted to reduce the size of overshoot only for model versions that included the effects of MOC efferent feedback. These findings suggest that overshoot in normal and hearing-impaired listeners is mediated by some form of dynamic range adaptation other than what is observed in the auditory nerve of anesthetized animals. Mechanisms for this adaptation may occur at several levels along the auditory pathway. Among these mechanisms, the MOC reflex may play a leading role.

The medial olivocochlear reflex (MOCR) has been hypothesized to provide benefit for listening in noise. Strong physiological support for an anti-masking role for the MOCR has come from the observation that auditory nerve (AN) fibers exhibit reduced firing to sustained noise and increased sensitivity to tones when the MOCR is elicited. The present study extended a well-established computational model for normal-hearing and hearing-impaired AN responses to demonstrate that these anti-masking effects can be accounted for by reducing outer hair cell (OHC) gain, which is a primary effect of the MOCR. Tone responses in noise were examined systematically as a function of tone level, noise level, and OHC gain. Signal detection theory was used to predict detection and discrimination for different spontaneous rate fiber groups. Decreasing OHC gain decreased the sustained noise response and increased maximum discharge rate to the tone, thus modeling the ability of the MOCR to decompress AN fiber rate-level functions. Comparing the present modeling results with previous data from AN fibers in decerebrate cats suggests that the ipsilateral masking noise used in the physiological study may have elicited up to 20 dB of OHC gain reduction in addition to that inferred from the contralateral noise effects. Reducing OHC gain in the model also extended the dynamic range for discrimination over a wide range of background noise levels. For each masker level, an optimal OHC gain reduction was predicted (i.e., where maximum discrimination was achieved without increased detection threshold). These optimal gain reductions increased with masker level and were physiologically realistic. Thus, reducing OHC gain can improve tone-in-noise discrimination even though it may produce a "hearing loss" in quiet. Combining MOCR effects with the sensorineural hearing loss effects already captured by this computational AN model will be beneficial for exploring the implications of their interaction for the difficulties hearing-impaired listeners have in noisy situations.