Is off-frequency overshoot caused by adaptation of suppression?
Bottom Line: This study is concerned with the mechanism of off-frequency overshoot.Overshoot refers to the phenomenon whereby a brief signal presented at the onset of a masker is easier to detect when the masker is preceded by a "precursor" sound (which is often the same as the masker).Overshoot is most prominent when the masker and precursor have a different frequency than the signal (henceforth referred to as "off-frequency overshoot").
Affiliation: , Nottingham, UK.
This study is concerned with the mechanism of off-frequency overshoot. Overshoot refers to the phenomenon whereby a brief signal presented at the onset of a masker is easier to detect when the masker is preceded by a "precursor" sound (which is often the same as the masker). Overshoot is most prominent when the masker and precursor have a different frequency than the signal (henceforth referred to as "off-frequency overshoot"). It has been suggested that off-frequency overshoot is based on a similar mechanism as "enhancement," which refers to the perceptual pop-out of a signal after presentation of a precursor that contains a spectral notch at the signal frequency; both have been proposed to be caused by a reduction in the suppressive masking of the signal as a result of the adaptive effect of the precursor ("adaptation of suppression"). In this study, we measured overshoot, suppression, and adaptation of suppression for a 4-kHz sinusoidal signal and a 4.75-kHz sinusoidal masker and precursor, using the same set of participants. We show that, while the precursor yielded strong overshoot and the masker produced strong suppression, the precursor did not appear to cause any reduction (adaptation) of suppression. Predictions based on an established model of the cochlear input-output function indicate that our failure to obtain any adaptation of suppression is unlikely to represent a false negative outcome. Our results indicate that off-frequency overshoot and enhancement are likely caused by different mechanisms. We argue that overshoot may be due to higher-order perceptual factors such as transient masking or attentional diversion, whereas enhancement may be based on mechanisms similar to those that generate the Zwicker tone.
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Mentions: According to the adaptation-of-suppression model of overshoot, the precursor should have reduced the suppressive masking of the signal by the masker. This should have increased the response to the signal and thus its forward-masking effect on the probe, causing an increase in probe detection threshold. This, however, was not observed. Instead of an increase, the precursor caused a small (1.5 ± 0.2 dB on average) but significant [t (4) = −10.2, p = 0.001] decrease in probe detection threshold (Fig. 5). A similar (0.9 ± 0.9 dB on average) albeit non-significant [t (4) = −1.0, p = 0.359] decrease in the probe detection threshold due to the precursor was also observed in the control experiment, where the probe detection threshold was measured in the presence of the masker alone, or the masker and precursor combined. The precursor effects in the adaptation-of-suppression and control experiments were not significantly different from one another [t (4) = −0.6, p = 0.573].FIG. 5
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