Transient masking and the temporal course of simultaneous tone-on-tone masking

Abstract

Previous studies have shown that threshold for a signal in tone-on-tone simultaneous masking is sometimes lower when the masker is continuous than when it is gated. Threshold may also decline as signal onset is delayed relative to the onset of a longer duration masker, though it may increase again near masker offset. In the present study, the level of a 1250-Hz sinusoidal masker was found which would just mask a 20-ms, 1000-Hz sinusoid presented at 10-dB sensation level (SL). Masker duration was 20 or 400 ms; in the latter case, the signal was presented in one of three temporal positions within the masker. The level of the 1250-Hz masker necessary to mask the signal was reduced, sometimes by as much as 20-25 dB, by a 20-ms, 500-Hz sinusoid (transient masker) presented at the times when the signal might occur, but at a level 30 dB below that at which it would mask the 10-dB SL signal. This suggests that, in the earlier studies, at least some of the elevation in threshold in the presence of a short-duration masker or at the beginning (or end) of a longer duration masker may have been due to the transient responses to the masker affecting detection of the signal, but not necessarily masking the signal in terms of excitation in the signal "channel."

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

“…The off-frequency component of the overshoot effect is consistent with an explanation invoking central mechanisms proposed by Bacon and Moore (1987). They noted that, for a sinusoidal masker with a frequency abovefs, signal threshold was higher at short than at long values of At, leading to an overshoot effect.…”

“…However, thresholds are sometimes higher in the "gated" condition than at At = 0 ms, probably because transient responses to the masker offset interfere with detection of the signal (e.g., Elliott, 1965;Bacon and Moore, 1987). Similarly, thresholds at long At's can be slightly higher than those obtained with continuous maskers, because transient responses to the masker offset may raise thresholds when the masker is turned off shortly after the signal (Carlyon, 1987;McFadden, 1989).…”

Enhancing a tone by shifting its frequency or intensity

“…The separate-tone percept may be elicited even if the second sound (called hereafter the "test sound") has in fact a flat spectral profile, while the first sound (the "precursor") has a spectral notch. An important difference between this "enhancement" effect and the previously described overshoot effect is that, in the enhancement effect, the detection of a change is not reducible to the detection of a transient since all the spectral components of the test sound are gated on synchronously (see in this respect Macmillan, 1971Macmillan, , 1973Bacon and Moore, 1987;Hafter et al, 1998;Gallun, 2003, Chap. 3).…”

Effects of age and hearing loss on overshoot

“…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). The improvement in thresholds for the probe presented near the center of the masker is hypothesized to occur because the probe's onset occurs much later than the masker's onset, thus reducing transient masking.…”