Abstract:

For normal-hearing listeners, harmonic complexes with equivalent power spectra but which differ in temporal waveform shape (i.e., in phase spectra) may also differ in their effectiveness as maskers. Summing harmonic components in positive-Schroeder phase generally produces a less effective masker than a negative-Schroeder complex [Kohlrausch and Sander, J. Acoust. Soc. Am. 97, 1817--1829 (1995)]. This influence of phase structure on masking effectiveness may reflect nonlinear compressive processing in a healthy cochlea [Carlyon and Datta, J. Acoust. Soc. Am. 99, 2542 (1996)]. This study measured detection thresholds of normal-hearing and hearing-impaired listeners for tones masked by complexes in positive- and negative-Schroeder phase. Masker stimuli contained all harmonics between 200 and 5000 Hz of a 100-Hz fundamental with harmonics set equal in amplitude. Three probe frequencies (1000, 2000, and 4000 Hz) and three probe levels (60, 70, and 80 dB SPL) were tested. For normal-hearing listeners, positive-Schroeder stimuli were consistently less effective maskers than negative-Schroeder complexes, particularly at the 60-dB probe level. Differences in masker phase structure had less effect at high presentation levels and for hearing-impaired listeners. The results are consistent with nonlinear compressive auditory processing by normal-hearing listeners which is reduced at high presentation levels and in the presence of sensorineural hearing loss. [Work supported by NIH.]