Evidence from behavioral studies suggests that modulation detection interference (MDI) may be attributed to masker-probe interactions within a peripheral auditory channel or across peripheral auditory channels. Within-channel interactions between the masker and probe carriers could decrease the depth of modulation of the

probe, increasing the difficulty of detecting amplitude modulation [Bacon and Moore, 1993]. Alternatively, a

modulation detection process dependent on across-channel comparisons might be compromised if the modulation envelopes of the masker and probe were similar [Yost and Sheft, 1994]. Insight into the physiological mechanisms responsible for MDI in humans is provided by investigating the auditory steady-state response (ASSR) to multiple amplitude-modulated stimuli. Three ASSR experiments were designed to approximate conditions evaluated in the behavioral MDI paradigm. The subjects were 32 normal-hearing adults. During each experiment, probe and interfering tones were paired to record electrophysiological responses. The effects of carrier frequency, modulation depth and modulation rate of the interfering tone on ASSR amplitudes were evaluated. Experiment 1 revealed that ASSR amplitudes were reduced when a higher frequency interfering tone was paired with the probe tone, and when the interfering tone was modulated at a lower modulation depth than the probe tone. Experiment 2 revealed that ASSR amplitude reductions were dependent on the spectral proximity of the probe and interfering tones. Experiment 3 indicated that ASSR amplitude reductions were greater when the probe and interfering tones were modulated at different rates. Analogous findings of this investigation and previous behavioral evaluations are supportive of within-channel contributions to MDI.