Modulation detection interference: Interference for discriminating a change in the depth of amplitude modulation

Abstract

Discrimination of a change in the depth of sinusoidal amplitude modulation of a sinusoidal probe carrier was measured in a modulation detection interference (MDI) paradigm (discrimination between [1 + mb cos(2πfmt)] [cos)2πfρt)] and [1 + mρ cos(2πfmt)] × [cos(2πfρt)], where mb = baseline depth of modulation; mρ = probe‐tone modulation depth to be discriminated from mb; fm = amplitude modulation rate; and fc = carrier frequency). Three conditions were tested for each carrier frequency (1000 and 4000 Hz) and baseline depth (0%, 25%, 50%, 75%, and 100%): probe alone conditions depth discrimination was measured for the probe‐tone carrier presented by itself; unmodulated masker condition—depth discrimination was measured for the probe‐tone carrier when an unmodulated masker tone was simultaneously presented at the other tonal carrier frequency; and modulated masker condition—depth discrimination was measured when the masker tone was sinusoidally amplitude modulated at 100% depth and at the same rate (11, 20, or 32 Hz) as the probe tone. The depth of discrimination thresholds averaged over five listeners for both probe‐tone carrier frequencies for all three modulation rates, and for both the probe alone and unmodulated masker conditions, was approximately the same and decreased as the baseline depth increased from 0% to 100%. However, depth discrimination thresholds increased dramatically for all modulated masker conditions that indicated significant modulation detection interference for depth discrimination as has been shown for modulation detection and modulation rate discrimination [Yost et al., J. Acoust. Soc. Am. 86, 2138–2147 (1989)]. The results will be discussed in terms of cross‐spectral modulation interactions. [Work supported by NIDCD and AFOSR.]