Abstract
Frequency DL's were determined for twenty un-practiced subjects in two separate tasks using a two-interval forced-choice technique. In the first task subjects were required to decide which one of two tones was modulated in frequency, when one of the tones was modulated at a rate of 4 Hz. In the second task subjects were required to decide which of the two steady tones had the higher pitch. The DL's corresponding to 75% correct decisions were determined by a ‘staircase’ method. Each subject was tested twice for each task, in sessions separated by about one week. Frequency DL's for modulated tones did not correlate significantly with those for steady tones, indicating that the two kinds of DL's are measures of separate auditory abilities. DL's for steady tones differed widely among subjects, and showed a fairly large practice effect. By contrast, the DL's for modulated tones differed little among subjects, and showed a smaller practice effect. Both tasks seem to be reliable as indicated by the high test-retest correlations. It is suggested that the DL for frequency modulation, measured in a forced-choice task, might be a useful clinical tool, as a measure of the frequency resolution of the auditory system.