Spectral differences in the ability of temporal gaps to reset the mechanisms underlying overshoot

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Abstract
When very brief tonal signals are presented immediately after the onset of a gated noise masker, detectability can be 10–20 dB worse than when the signal is delayed by several hundred milliseconds, an effect known as the overshoot. It has long been known that, when an ‘‘onset’’ is created in an otherwise continuous, broadband masker by briefly turning it off and on again, the detectability of a brief signal presented soon after this temporal gap will decline gradually as the gap is increased from a few milliseconds to a few hundred milliseconds. In other words, the auditory system recovers to its quiescent, resting state following an adequate silent interval. Here, the broadband maskers consisted of three adjacent spectral bands—one centered on the frequency of the tonal signal, one low passed below the lower edge of the center band, and one high passed above the upper edge of the center band. The signal was a 2500‐Hz tone having a total duration of 6 ms. In different blocks of trials, either all three bands, only the center band, or only the two flanking bands were temporally gapped by a duration ranging from 10–300 ms. When the center band was about 750 Hz wide (about 2.5 critical bandwidths), this differential gapping process resulted in typical recovery functions when all three bands (the entire spectrum) or when just the two flanking bands were gapped. However, when only the center band was gapped, there was n o evident recovery—rather, detectability remained near the signal level required with a continuous masker, even for a gap duration of 300 ms. That is, the process of recovery required that spectral regions a d j a c e n t t o the 750 Hz centered on the signal frequency be temporally gapped; gapping the frequency components actually doing the masking was neither sufficient nor necessary. Once the center band was made 3000 Hz wide, and the flanking bands were made correspondingly narrower, gapping the center band d i d yield a typical recovery function—presumably because the relevant, adjacent spectral regions were now being affected by the gapping process—and gapping the relatively narrow, and remote, flanking bands did not produce a recovery function. These outcomes reveal that the standard neurophysiological explanation of the overshoot effect needs to be extended to include the contributions of adjacent frequency regions.

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