Monotic and dichotic modulation detection interference in practiced and unpracticed subjects.

The threshold for detecting 10-Hz amplitude modulation of a 1-kHz carrier was measured in quiet and in the presence of a 4-kHz masker carrier that was either unmodulated or amplitude modulated at a depth of 1.0 and at rates from 2 to 80 Hz. The signal and masker were presented to the same ear (monotic condition) or to opposite ears (dichotic condition), and the subjects either had no previous experience with psychoacoustic experiments (n = 10) or had from 16 to about 70 h of experience with modulation-detection tasks (n = 4). There were no significant differences between the two groups of subjects, although there was a significant effect of presentation mode. Thresholds generally were higher in the monotic condition, particularly when the masker rate was similar to the signal rate. According to excitation-pattern analyses, the greater interference in the monotic condition is unlikely due to peripheral interactions.