DISCRIMINATION OF CHANGES IN THE SPECTRAL SHAPE OF NOISE BANDS

Discrimination experiments were performed for a change in the spectral shape of noise bands. The subject's task was to discriminate noise ba nds with a positive spectral slope from those with a negative spectral slope. Thresholds were: measured at several bandwidths and center fre quencies, as well as for several noise samples. Experiments were perfo rmed while roving the overall intensity. At a fixed center frequency o f 1 kHz, sensitivity was best for bandwidths of 3-6 semitones (ST). At larger bandwidths, thresholds increased only slowly. At a fixed bandw idth of 1 ST, threshold hardly changed as a function of the center fre quency. At a fixed bandwidth of 58 Hz, threshold was lowest near 500-1 000 Hz. Model calculations show that the EWAIF model [Feth, Percept. P sychophys. 15, 375-378 (1974)] can account for the present results if the signal's bandwidth does not exceed 1 ST. The IWAIF model [Ananthar aman et al., J. Acoust. Soc. Am. 94, 723-729 (1993)] can account for t he present results only if the signal's bandwidth is smaller than 1 ST but larger than about 25 Hz. Results obtained with broadband signals could be described only qualitatively with the multichannel model [Dur lach etal., J. Acoust. Sec. Am. 80, 63-72 (1986)]. Then, the model nee ds the assumption that either the output of the different frequency ba nds cannot be optimally combined, or that only two bands are used in t he discrimination process. The present results are compared with those obtained with two-tone complexes measured under identical conditions [Versfeld and Houtsma, J. Acoust. Soc. Am. 98, 807-816 (1995)]. (C) 19 97 Acoustical Society of America. [S0001-4966(97)04110-6] PACS numbers : 43.66.Ba, 43.66.Fe [JWH].