A comparison of detection and discrimination of temporal asymmetry in amplitude modulation

Two compound experiments were performed to compare the detection of amplitude modulation with the discrimination of modulator shape when the modulators have strong temporal asymmetry. In experiment 1, an adaptive procedure was used to measure detection and discrimination as a function of modulation frequency from 4 to 400 Hz. In experiment 2, the method of constant stimuli was used to measure psychometric functions for detection and discrimination at one modulation frequency, 8 Hz. The asymmetric modulators were time-reversed pairs. Thus their envelope spectra are identical and models based on the envelope spectrum would predict no effect of asymmetry on detection or discrimination at any modulation depth. The detection results show, as predicted, that the direction of asymmetry does not affect the detectability of modulation in either experiment. In contrast, the discrimination results show that direction of asymmetry is readily discriminable for modulation frequencies less than about 50 Hz, indicating that envelope-spectrum models will require modification if they are to be extended to include discrimination of temporal asymmetry.