Abstract:

Green et al. [J. Acoust. Soc. Am. 66, 1051--1056 (1979)] reported that a psychometric function for detecting a 1000-Hz increment was two to three times steeper with a continuous rather than with a gated pedestal. Intrigued by their finding, the observations to frequencies of 250 and 4000 Hz were extended, and to signal types including tone in noise and noise in noise. Psychometric functions of three normal-hearing listeners were constructed from 2IFC adaptive tracks and fitted with a Gaussian function: pc=(Phi)(d[sup ']/[radical 2]), where d[sup ']=(x/(alpha))[sup (beta)], x is the signal level, (alpha) is the threshold, and (beta) is the slope. In all conditions, slopes obtained with continuous pedestals were steeper than those obtained with gated pedestals. For tone-in-tone conditions [x=10 log(1+(Delta)I/I)], slopes differed by a factor of 2 at 250 and 1000 Hz, and by a factor of 4 at 4000 Hz. For tone-in-noise conditions [x=E/N[inf 0]], slopes differed by a factor of 2 across the three frequencies. For noise-in-noise conditions [x=10 log(1+S[inf 0]/N[inf 0])], the slopes differed by a factor of 1.5. Implications of these data for existing models of intensity coding will be discussed. [Work supported by NIH/NIDCD.]