Stanley Sheft
William A. Yost
Parmly Hearing Inst., Loyola Univ., 6525 N. Sheridan Rd., Chicago, IL 60626
The ability to detect amplitude modulation (AM) of two concurrent tonal carriers was measured in a 4 AFC task; each carrier was independently modulated during one of two observation intervals. Carrier frequencies were 700 and 2350 Hz and AM rates were 4, 16, and 200 Hz. In the concurrent detection task, the modulation depths were either 1.0 or set for a detection d' of 0.7 or 2.0 with modulation of just one carrier. Results showed large performance decrements in the concurrent detection procedure that were greater than typically obtained in other two-channel listening tasks. Partitioning of the 4x4 response matrix indicated interaction between carrier channels with performance generally better when both tones were simultaneously modulated and for most subjects at the greater modulation depths when both responses were correct. Cross-channel estimates of correlation derived from the bivariate normal distribution were highly dependent on the subject's response strategy. When both tones were modulated at the same rate, results are consistent with past work indicating difficulty associating modulation with its appropriate carrier. Overall results indicate limited ability to independently process two concurrent sources of modulation information. [Work supported by NIH.]