4aPP1. AM detection with one- and two-tone modulators.

Session: Thursday Morning, May 16

Time: 8:00

Author: Stanley Sheft
Author: William A. Yost
Location: Parmly Hearing Inst., Loyola Univ., 6525 N. Sheridan Rd., Chicago, IL 60626


Psychometric functions were measured for detecting amplitude modulation (AM) of a wideband noise carrier that was either gated with the 400-ms modulator or was on continuously. AM rates were 5, 20, 80, and 2000 Hz. The functions were steepest at the 80-Hz AM rate and shallowest with 2-kHz AM. A linear regression of log d[sup '] on 20 log m showed the slope of the functions ranging from 0.83 to 1.59 in the gated conditions and from 1.34 to 1.79 in the continuous conditions. The increase in function slope between the gated- and the continuous-carrier conditions was less than predicted by Laming's model of sensory processing [D. Laming, Sensory Analysis (Academic, New York, 1986)]. AM detection ability was also measured with two-tone modulators centered at either 2 or 6.5 kHz. Modulator tones were separated by 5, 20, or 80 Hz. Performance with the two-tone modulators was often better than predicted by either the envelope rms or max/min value, especially with the tones centered at 6.5 kHz. This result is consistent with incorporation of a second nonlinearity into a model of auditory envelope detection, introducing intermodulation at the low-modulator beat rates. [Work supported by NIH.]

from ASA 131st Meeting, Indianapolis, May 1996