The Frequency Selectivity of Gain Reduction Masking: Analysis Using Two Equally-Effective Maskers

Abstract

The “temporal effect” occurs when masked threshold is shifted as a result of the signal being preceded by sound (i.e., a “precursor”) instead of silence. Several authors have suggested that the temporal effect may be mediated by the medial olivocochlear reflex (MOCR), which reduces the gain of the cochlear amplifier. We recently measured an analogous temporal effect in forward masking (Jennings et al., J Acoust Soc Am 125:2172-2181, 2009). This study estimated the basilar membrane input-output (I/O) function using psychophysical methods. When an on-frequency precursor was present, the gain of the I/O function decreased, consistent with the MOCR hypothesis. Here, we present data on the same forward masking temporal effect, but with specific interest on the tuning of the precursor’s effect. In experiment 1, off-frequency GOM was measured to estimate the I/O function. In experiment 2, psychophysical tuning curves (PTCs) were measured to estimate the tuning of the precursor for two signal levels. Finally, in experiment 3 we combined the masker levels from experiment 1 and the precursor levels from experiment 2 to measure the shift in signal threshold. In the discussion, we model these data in terms of gain reduction and additivity of masking. The results and modeling suggest that the precursor reduced the gain of the I/O function and that the resulting PTCs reflect the tuning of the gain reduction mechanism.