Temporal integration functions of AM detection and AM depth discrimination

Previous studies (Lee, 1994; Lee and Bacon, 1997) suggested that both AM rate and AM depth discrimination were influenced by the number of AM cycles, instead of by the duration of stimulus. AM detection and AM depth discrimination were measured as a function of the number of AM cycles for the modulation rates of 10, 20, 40, 80, 125, 160, and 320 Hz. The carrier was a broadband noise (10 kHz low pass), and the carrier was either gated with the modulator (gated carrier) or presented 250 ms earlier and 250 ms later than the modulator (continuous carrier). The overall level of each presentation was randomized within 6‐dB range from 65 dB SPL. For the lower modulation rates (10, 20, 40, and 80 Hz), there was a significant improvement with the continuous carrier at smaller number of cycles (two and four modulation cycles) as compared to the gated carrier condition. For the higher modulation rates (125, 160, and 320 Hz), however, the thresholds were not affected by carrier type. These results suggest that there might be a different temporal integration process for lower and higher modulation rates. [This work was supported by NIDCD Grant No. R03 DC06605‐02.]