ASA 125th Meeting Ottawa 1993 May

3aMU5. Comodulation masking release for AM noise maskers.

David A. Eddins

Beverly A. Wright

Psychoacoust. Lab., Psychol. Dept., Univ. of Florida, Gainesville, FL 32611

Comodulation masking release (CMR) was measured for a pure-tone signal (2500 Hz) masked by five narrow-band (100 Hz wide) noises (2IFC, 3-down/1-up paradigm). Nose bands were centered at 1500, 2000, 2500, 3000, and 3500 Hz and had a spectrum level of 50 dB SPL. The stimulus duration was 500 ms. Each band of noise was composed of 51 sinusoids. The noise envelopes were manipulated on two levels. On the first level, the phases and amplitudes of the 51 components were either the same (coherent) or different (incoherent) across the bands. On the second level, the bands were amplitude modulated with 10-Hz sinusoids and were either comodulated (same starting phase) or uncomodulated (phase shifted). Mean thresholds for three listeners were 69 and 63 dB SPL for incoherent and coherent noise, respectively, yielding a 6-dB CMR. For both incoherent and coherent noise, thresholds were lower in the presence of modulation. Thresholds were lower by about 3 dB for the uncomodulated noise and 21 dB for the comodulated noise. Thus a CMR occurred on the first level, incoherent minus coherent noise, and on the second level, uncomodulated minus comodulated noise. Combinations of the two treatments may augment or diminish the CMR. [Work supported by AFOSR and NIH.]