Amplitude modulation detection thresholds and associated psychometric functions

Amplitude modulation detection thresholds for broadband stimuli were measured as a function of modulation frequency in seven listeners with normal hearing. Two adaptive procedures (1-down, 1-up and 4-down, 1-up) were used to track the 50% and the 84% correct levels in a three-interval, three-alternative, forced-choice task. Preliminary data show that the temporal modulation transfer functions for the two criteria are parallel for lower modulation frequencies but tend to converge with increasing modulation frequency. The resultant two-point psychometric functions associated with the modulation detection data demonstrate an increase in slope with increasing modulation frequency. Time constants were calculated from a least-squares fit of the equation y=k/(f+a) and further illustrate the effects of the changes in psychometric function slope. These data have implications for comparisons of temporal acuity estimates across data sets.