Detecting amplitude modulation of sinusoidal carriers

Abstract

Listeners were asked to detect sinusoidal amplitude modulation (SAM) of one carrier tone (the target carrier) in the presence of a second carrier tone (the masking carrier) that also had SAM. The depth of modulation required to detect the presence of SAM of the target carrier was measured as a function of the difference in the frequency of amplitude modulation for the two carriers (modulator frequencies ranged from 4 to 100 Hz), the frequency separation between the two carriers (200- to 3000-Hz separation), and the phase of the sinusoidal modulator of the masker carrier relative to the phase of the sinusoidal modulator of the target carrier. In half of the conditions, the frequency of the target carrier was greater than the frequency of the masker carrier, while, for the other half of the conditions, the frequency of the target carrier was less than that of the masker carrier. The data will be discussed in terms of the strategies employed by the auditory system in processing temporal modulation of complex sounds. The data indicate that the auditory system uses a wideband mode for processing temporal modulation, such that there is a great deal of interaction across widely separate frequency channels. [Work supported by the NINCDS.]