Effects of amplitude modulation on profile detection using multiple short signals

Abstract

The detection of an increment in a target component is more difficult when the surrounding, nontarget components are sinusoidally amplitude modulated [H. Dai and D. Green, J. Acoust. Soc. Am. 90, 836–845 (1991)]. The purpose of the present study was to determine whether the detrimental effects of amplitude modulation (AM) on profile analysis could be eliminated by providing a relatively ‘‘static’’ profile during the course of AM. The task was to detect an increment in a 1‐kHz target component that was centered in a complex containing 21 logarithmically spaced components ranging in frequency from 200 to 5000 Hz. The target component was always unmodulated whereas the nontarget components were either unmodulated or sinusoidally amplitude modulated at a rate of 10 Hz. The signal was composed of multiple 20‐ms presentations, all positioned at successive peaks, valleys, or leading edges of the modulation cycle. As in previous work with longer signals, thresholds generally increased with increasing modulation depth. An attempt to account for the effects of AM in terms of the short‐term pedestal resulting from the modulation was only marginally successful. [Work supported by NIH and Sigma Xi.]