Effects of practice and signal energy on duration discrimination of brief auditory intervals.

In Experiment 1, the proposition that duration discrimination of filled auditory intervals is based on temporal information rather than on energy-dependent cues was tested in 64 naive subjects. The subjects were presented with two auditory stimuli at different levels of intensity within one trial, and had to decide which of the two was longer in duration. An adaptive psychophysical procedure was used. As a measure of performance, difference threshold estimates in relation to a 50-msec standard interval were computed. Duration discrimination showed no effect of energy values, indicating that the subjects' discrimination was independent of stimulus intensity. The goal of Experiments 2A and 2B was to investigate the effects of practice on duration discrimination which, in addition, may provide an indirect test for the potential use of energy-dependent cues. Effects of practice on duration discrimination of filled (Experiment 2A) and empty (Experiment 2B) intervals were studied in 6 subjects in each case, over 20 testing sessions. An adaptive psychophysical procedure that was similar to the one used in Experiment 1 was applied. Neither short-term effects of practice based on the first five testing sessions, nor long-term effects of practice based on the means of 4 consecutive weeks, could be demonstrated. The results of the present study suggest that duration discrimination of brief auditory intervals is based on temporal information and not on stimulus energy. Furthermore, implications for the notion of a very basic biological timing mechanism underlying temporal processing of brief auditory intervals in the range of milliseconds are discussed.