Experiments related to the detection of a tone masked by another tone

Five experiments were completed in an effort to determine which cues allow the detection of a tone in the presence of another tone of a different frequency. Four cues associated with the added tone were examined (a) changes in overall level, (b) changes in envelope modulation (beats), (c) changes in pitch, and (d) changes in phase (frequency) modulation. Detection thresholds were measured using a two-interval, forced choice paradigm, and for maskers of 400 and 3000 Hz. The data suggest that the presence of beats acts as a cue for detection when the signal and masker frequencies are within ten percent of one another. For larger frequency separations the data did not support any of the detection models examined [(a)-(d) above]. Based on limited direct observations and on the failure of the single-channel models tested, it appears that the detection of a tone in the presence of another tone depends on the detection of changes in the pattern of intensity and/or the pattern of temporal synchrony across frequency.