The role of envelope cues for the detection of a tone added to a narrow band of noise

Abstract

Using a 21FC paradigm, psychometric functions for the detectability of a tonal signal added to a 40‐Hz‐wide band of Gaussian noise was measured using signal and center frequencies of 600, 1800, and 5400 Hz. In a second condition, the noise‐alone and the tone‐plus‐noise stimuli were scaled so as to yield identical energy values across the two intervals of each trial. Under the assumption of optimal combination of independent cues, a comparison of these conditions allows an estimate of the relative contribution of energy‐based and non‐energy‐based cues for the detection of a tone added to noise. In a third condition, the envelopes of the scaled noise‐alone and tone‐plus‐noise stimuli were extracted, and used to modulate tones of either 600, 1800, or 5400 Hz. The ability to discriminate between envelope patterns was measured, and that measure used to estimate each observer's reliance on envelope‐based cues. Large individual differences were obtained. For one observer, the detection of a tone added to Gaussian noise was determined to rely equally on envelope‐based and energy‐based cues. A second observer was found to depend almost wholly on changes in energy. None of the observers appeared to rely on changes in fine structure that occur when a tone is added to noise, and consistent with that observation, no differential effect of frequency region was obtained. [Work supported by the National Institutes of Health.]