Increment and decrement detection as a measure of auditory temporal resolution

The temporal resolution of the auditory system, or its ability to follow rapid fluctuations, is fundamental to the processing of all acoustic stimuli, including speech. A popular method of determining temporal resolution is to measure thresholds for detecting a brief decrement in the level of an otherwise continuous sinusoid. Background noise is often added in such experiments in order to mask 'spectral splatter'. Current models assume that detection is achieved if the maximum 'dip' in a smoothed internal representation of the stimulus exceeds a certain criterion level. The experiment described here was designed to test these models. Thresholds were measured for several durations of increments as well as decrements using a wide range of background-noise levels. Two important aspects of the results are not consistent with current models. Firstly, at short durations, there was a large asymmetry between increments and decrements; decrements were less easily detected than increments. Secondly, results were highly dependent on the level of the background noise. The data show the need for a revision of current models of temporal resolution, and cast doubt on the suitability of decrement detection as a measure of temporal resolution.