Detection and discrimination of second-order sinusoidal amplitude modulation (SAM)

Abstract

The perception of complex temporal envelopes has been recently studied using second-order SAM [Lorenzi et al., J. Acoust. Soc. Am. 110, 1030 (2001)]. In these stimuli, the modulation depth of a SAM signal (of rate fm) is sinusoidally amplitude-modulated at a rate fm′, thereby generating two additional components at fm±fm′ in the modulation spectrum, and a slow beat at fm′ in the temporal envelope. The present study investigates the respective contribution of these two cues to the perception of second-order SAM. In four normal-hearing listeners, second-order SAM detection and rate-discrimination abilities are measured at a high ‘‘carrier’’ (fm=256 Hz), but low beat rates (fm′≤128 Hz), as a function of stimulus duration (250 ms to 2 s). The data are compared to first-order SAM detection and rate-discrimination thresholds measured in similar conditions at 1≤fm≤128 Hz. At common modulation rates (fm=fm′), the results show that (i) first- and second-order thresholds increase similarly when stimulus duration decreases, and (ii) first- and second-order SAM rate-discrimination thresholds are basically identical. The data therefore indicate that detection and discrimination of second-order SAM are mainly based on the slow temporal envelope beat cue.