Continuous versus gated pedestals and the ‘‘severe departure’’ from Weber’s law

Abstract

Thresholds were compared for the detection of 20-ms sinusoidal signals presented with either continuous or gated sinusoidal pedestals of the same frequency (500 or 6500 Hz). Pedestal levels ranged from 35-80 dB SPL. For 500-Hz signals, thresholds were lower in the continuous-pedestal condition than in the gated-pedestal condition, for all pedestal levels above 35 dB SPL. When the pedestal level was 35 dB, thresholds were higher in the continuous-pedestal condition than in the gated-pedestal condition. This was also true at all pedestal levels when bandstop noise centered around the pedestal frequency was added to the pedestal. For 6500-Hz signals, a deterioration in performance at intermediate levels, similar to that reported by Carlyon and Moore [J. Acoust. Soc. Am. 76, 1369-1376 (1984)], was found in the gated-pedestal condition. No such deterioration occurred in the continuous-pedestal condition. However, masking signal onsets and offsets by bursts of bandpass noise produced a midlevel deterioration in the continuous-pedestal condition. This was true when bandstop noise was absent, and when it was gated on and off in each observation interval. When continuous bandstop noise was present, no midlevel deterioration was observed, even when onsets and offsets were masked. The results suggest that in the continuous-pedestal condition subjects may normally maintain performance across level at 6500 Hz by attending to a transient response to signal onsets. Presenting bursts of bandpass noise disrupts the detection of such a response. The absence of a midlevel deterioration when continuous bandstop noise was present may be related to the adaptation to the sinusoidal pedestal that was caused by the bandstop noise.

The effects of masking on the growth of vibrotactile sensation magnitude and on the amplitude difference limen: A test of the equal sensation magnitude-equal difference limen hypothesis

“…This method produces lower DLs than those obtained with the gated-pedestal method in which subjects detect differences in amplitude between two successive bursts of stimulation (Gescheider et al, 1990). Consistent with this is the finding that auditory DLs measured by the continuous pedestal method have also been found to be lower than those measured by the gated pedestal method (Carlyon and Moore, 1986;Campbell and Lasky, 1967;Green, 1969;Green et al, 1979;Turner et al, 1989;Viemeister and Bacon, 1988;Zwicker and Fastl, 1972). •' Another factor that has been found to influence the size of the amplitude-difference DL in vibrotaction is the presence of a masking stimulus.…”

The relation between loudness and intensity difference limens for tones in quiet and noise backgrounds

“…Weber functions for the tone in noise (dashed curves) demonstrate the near-miss for S3, but deviations of another type are apparent for the other three subjects--namely, an increase in the size of the relative DLs occurs at intensities of 80-90 dB SPL. Other researchers have reported a somewhat similar "bump" in the Weber function for clicks (Raab and Taub, 1969), and, for high-frequency, short-duration tones (Carlyon and Moore, 1984Moore, , 1986a, although it is not clear that the origins of the bumps are related.…”

Auditory enhancement of changes in spectral amplitude

“…Similar, but generally smaller, differences in theshold are found with sinusoidal maskers, but only for conditions where the masker is at, or above, the frequency of the signal (e.g., Bacon and Viemeister, 1985a, b). Bacon and Viemeister (1985a) and Carlyon and Moore (1986) have noted qualitative parallels between these effects and the incremental response of primary auditory-nerve fibers. Now consider the situation when a missing component is reintroduced into an incomplete harmonic series.…”