Interactions of masker bandwidth with signal duration and delay in forward masking

Abstract

Forward-masked thresholds for 1-kHz sinusoidal signals were measured as a function of the bandwidth of a noise masker centered at 1 kHz, using a two-interval forced-choice technique. The noise spectrum level was 40 dB SPL/Hz, and noise bandwidth was varied from 50 to 1600 Hz. In experiment I signal duration was varied, with a fixed offset-onset time of 5 ms between masker and signal. For the shortest signal (5 ms) threshold at first increased with increasing bandwidth and then decreased. As signal duration increased, the bandwidth at which maximum masking occurred (the rollover bandwidth) decreased, and for the longest signal (45 ms) maximum masking occurred for the narrowest bandwith tested. In experiment II the silent interval between masker and signal was varied, for a signal of 5-ms duration. Again threshold at first increased with noise bandwidth, and then decreased. However, the rollover bandwidth decreased with increasing silent interval, and threshold varied less with bandwidth. In experiment III signal duration was varied for a fixed offset-offset time of 50 ms between masker and signal. Changes in threshold with noise bandwidth were small, except for the longest signal (45 ms) for which threshold increased markedly at the narrowest bandwidth used. For the wider nose bandwidths, threshold decreased gradually with increasing signal duration, whereas for the narrowest noise bandwidth, threshold increased with increasing duration. It is argued that interactions of excitation and suppression within the internal representation of the masker influence the results, but at least two other factors, detection of energy splatter in the spectrum of the signal and the presence or absence of quality differences between masker and signal, have a powerful influence.

Forward masking by sinusoidal and noise maskers

“…For example, a brief sinusoidal signal following a narrow-band noise will not be very different in quality from the noise, whereas for a wider noise bandwidth, the signal may have a more tonal quality in comparison to the noise. Interactions between masker bandwidth and signal duration consistent with this explanation have been observed by Moore (1981).…”

Confusion effects with sinusoidal and narrow-band noise forward maskers

“…Narrow-band noise maskers Moore ( 1981 ), Glasberg ( 1982, 1985), and Neff and Jesteadt (1983) have observed clear evidence of large confusion effects with 50-or 60-Hz-wide narrow-band maskers centered on the signal frequency. The signals were sinusoids ranging in duration from 20 to 45 ms.…”

“…In contrast, a number of studies of simultaneous masking have demonstrated the effectiveness of a contralateral masker, a phenomenon known as central masking (see Zwislocki, 1978, for a review). Although low-level ipsilateral stimuli have also been used as temporal cues in forward masking (Moore, 1981;Moore and Glasberg, 1982, 1985, the use of a contralateral cue provides a clearer test of confusion effects because the contralateral stimulus itself cannot mask the signal nor can it act as a suppressor. With either the ipsilateral or contralateral cues, extensive practice may be necessary before listeners learn to make effective use of the cues.…”

“…The for-1980), sinusoids (Neff and Jesteadt, 1983;Shannon, 1975), or narrow-band noise Glasberg, 1982, 1985;Neff and Jesteadt, 1983;Weber and Green, 1979). In three studies, ipsilateral stimuli were used to examine confusion effects for sinusoidal and broadband noise maskers (Moore and Glasberg, 1983) or narrow-band noise maskers (Moore, 1981;Moore and Glasberg, 1985).…”

Comparison of auditory filter shapes derived with three different maskers

“…The difference was similar for all three masker types, and is much smaller than has been found for psychophysical tuning curves (PTCs}, which typically have bandwidths about 50% smaller in forward masking (Wightman et al, 1977;Moore, 1978;Vogten, 1978}. We feel that the greater difference found for PTCs is at least partly the result of factors other than suppression (see Moore, 1978; O'Loughlin and Moore, 1981;, for a discussion of these factors}. Hence the smaller differences found in the present study may give a more accurate indication of the effects of suppression.…”