INFLUENCE OF RELATIVE LEVEL ON MODULATION DISCRIMINATION INTERFERENCE

This experiment examines the effects on modulation discrimination inte rference (MDI) of differences in level between the signal and masker c arriers. The task was to detect a change in depth of amplitude modulat ion of a 1-kHz signal carrier, in the presence of modulated or unmodul ated masker carriers that were either reasonably close to the signal c arrier frequency (540 and 1380 Hz) or distant from it (230 and 3300 Hz ). The relative level of the signal and masker carriers was systematic ally varied. The results show that modulated maskers can impair the de tection of changes in modulation depth even when the maskers are dista nt in frequency from the signal carrier and 30-30 dB lower in level th an the signal carrier. The magnitude of the interference effect change s only slowly with relative level of the signal and masker carriers, s uggesting that the interference depends primarily on across-channel pr ocesses.