Detection and intensity discrimination of a sinusoid

TLDR

The study discusses results in terms of nonlinear transduction, uncertainty, and contrast mechanisms proposed by Laming. Intensity discrimination thresholds for 100‑ms, 1000‑Hz tones were measured at multiple intensities near threshold and at 30, 60, and 90 dB SPL, with psychometric functions obtained for discrimination and detection in quiet and in broadband noise. Weber’s law holds approximately down to 0 dB SL, small negative masking occurs even in increment energy, discrimination psychometric functions are shallower than detection, and performance in broadband noise is similar but shows different variability.

Abstract

Intensity discrimination thresholds were measured for gated 100-ms, 1000-Hz tones. Discrimination thresholds were measured at several intensities near absolute threshold as well as at 30, 60, and 90 dB SPL. Psychometric functions were obtained for several of these discrimination conditions, and for detection of the signal in quiet. The results showed that Weber’s law is approximately valid for standards as low as 0 dB SL. Small amounts of negative masking were observed even when the data were expressed in terms of increment energy. The psychometric functions for the discrimination conditions had a similar form and were shallower than the psychometric function for the detection of a signal in quiet. A similar set of conditions was run in the presence of a continuous, broadband noise. The results were generally in agreement with those obtained in quiet, but slight differences suggested that the variability which limits performance in the two conditions is different. The results are discussed in terms of the effects of nonlinear transduction, the effects of uncertainty, and contrast mechanisms as proposed by Laming [Sensory Analysis (Academic, London, 1986)].