Effect of signal frequency and masker level on the frequency regions responsible for the overshoot effect

Abstract

Two experiments investigated the relative influence of components close to and remote from the signal frequency (fs) on the overshoot effect. Overshoot was defined as the difference in threshold between a signal presented 4 ms after, and that for one presented 300 ms after, the onset of a 350-ms masker. Experiment 1 measured the overshoot effect using both wideband and narrow-band maskers (centered on fs), at two signal frequencies and three masker levels. Experiment 2 used a masker consisting of a "middle band" (MB, centered on fs) and two flanking bands (FBs, which, when combined with the MB, produced a flat wideband spectrum). The masker was continuous except for a 300-ms interval just prior to the signal, during which either all three bands, the MB alone, or the FBs alone were turned off. The results of both experiments showed that the overshoot effect was usually determined by off-frequency components. However, the on-frequency components played a substantial role when signal-to-noise ratios (SNRs) at threshold were unusually high, such as at fs = 6500 Hz and intermediate masker levels. It is suggested that two different mechanisms contribute to the overshoot effect: an off-frequency mechanism which operates at all fs and masker levels, and an on-frequency mechanism which contributes to the overshoot effect only at high-threshold SNRs.

Effects of age and hearing loss on overshoot

“…Strickland (2004) thus limiting the amount of gain reduction applied to the probeþmasker and masker alone. In contrast, overshoot measured with slightly lower probe frequencies (e.g., 2.5 kHz) has been shown to increase and then plateau as a function of probe level (Carlyon and White, 1992), consistent with the current results for the 2-kHz probe (i.e., overshoot did not decrease at high probe levels).…”

“…This may be due to the lower masker levels in this study, or the tracking procedure which adapted on masker level rather than probe level. Indeed, consistent with the current study, Strickland (2004) measured thresholds by adapting on masker level and reported only a modest decrease in overshoot at high probe levels (or no decrease in some subjects) compared to studies that adapted on probe level (Bacon, 1990;Carlyon and White, 1992;Overson et al, 1996). Moreover, the masker level at which maximum overshoot is observed is highly variable among listeners.…”

“…Differences in the GOM slope between the 2-and 198-ms delay conditions and the finding that overshoot is decreased in listeners with cochlear hearing loss are difficult to explain by theories of overshoot based on confusion effects (Carlyon and White, 1992;Fletcher et al, 2015). These theories posit that overshoot is due to confusion between the onset of the probe and the onset of the masker (i.e., "transient masking"; Bacon and Moore, 1987).…”

“…3; squares, left bottom panel), consistent with the significant probe level*probe frequency interaction. Several studies reported a decrease in overshoot at high probe levels for probe frequencies at and above 4 kHz (Bacon, 1990;Carlyon and White, 1992;Overson et al, 1996). Strickland (2004) thus limiting the amount of gain reduction applied to the probeþmasker and masker alone.…”

“…Several peripheral (Smith and Zwislocki, 1975;Schmidt and Zwicker, 1991;von Klitzing and Kohlrausch, 1994;Strickland, 2001) and central (Carlyon and White, 1992;Fletcher et al, 2015) mechanisms have been proposed to explain overshoot. Of these mechanisms, the medial olivocochlear (MOC) reflex is most consistent with a reduction in cochlear amplifier gain, as suggested by psychophysical studies (Schmidt and Zwicker, 1991;Turner and Doherty, 1997;Bacon and Healy, 2000;Strickland, 2001Strickland, , 2004Strickland, , 2008Jennings et al, 2011).…”