Detection and intensity discrimination of a sinusoid with and without masker uncertainty

Abstract

The effect of stimulus-based uncertainty on the shape of the masking function at circa-threshold pedestal levels was investigated. Of particular interest was how uncertainty regarding properties of the masker affects the magnitude of “negative masking” [Raab et al., J. Acoust. Soc. Am. 35, 1053 (1963)] that is obtained under different stimulus configurations. Intensity discrimination thresholds for gated, 100-ms, 1000-Hz sinusoids were measured at three pedestal levels: -9, 0, and 9 dB re: absolute threshold. A two-interval, two-alternative forced-choice procedure was used. Under the reference condition, thresholds were measured in quiet. In comparison conditions, thresholds were measured in the presence of one of two masker types: (1) a notched-noise masker or (2) a random-frequency, multicomponent masker. In the multicomponent masker condition, uncertainty was imposed by roving the frequency components that comprised the masker from interval-to-interval over a block of trials. The data under each condition were fit with psychometric functions and slope estimates were obtained. Results are discussed with respect to the factors that govern, and possible mechanisms underlying, negative masking. Specifically, two possible explanations for the “dip” in the masking function are examined: nonlinear transduction [Hanna et al., J. Acoust. Soc. Am. 80, 1335 (1986)] and observer uncertainty.