Comodulation masking release as a function of masking noise-band temporal envelope similarity in normal hearing and cochlear impaired listeners.

Abstract

Thresholds for a pure-tone signal (1000 Hz) were obtained from both normal hearing and hearing-impaired listeners in a variety of masker conditions. Masking stimuli consisted of five Gaussian noise bands, each 20 Hz wide, and centered on 500, 750, 1000, 1250, and 1500 Hz. Two such base stimuli were created. In the first stimulus set, all noise bands had the same temporal envelope (comodulated). In the second set, each noise band was generated independently of the other bands, and thus each had independent temporal envelopes. Additional masking stimuli were generated by combining the comodulated and independent bands at specific comodulated/independent intensity ratios (CIR = 25, 20, 15, 10, and 5 dB), with overall level of the combined noise bands held constant. The result of increasing CIR was a progressive increase in the similarity of temporal envelopes of the noise bands masking the signal. Compared to threshold for the pure-tone signal in independent bands of noise, threshold steadily decreased as the CIR increased for normal hearing listeners. Cochlear-impaired subjects also showed decreased threshold with increasing CIR; however, the improvement was seen to plateau at relatively low CIRs. [Work supported by DRF and USARC.]