Profile-analysis models applied in two-tone complexes

Thresholds for changes in the amplitude of one or both components that compose two-tone complexes have been measured as a function of frequency separation. Thresholds have been measured while keeping the overall level fixed, or while using the within-trial roving level paradigm. Changes in the spectral shape of two-tone complexes were generally perceived better than changes in the overall level. Thresholds for the former changes are lowest at frequency separations near one semitone. Thresholds for the latter hardly depend on frequency separation. Two models have been applied to the data. For narrowbandwidth signals (smaller than~ ST, the EWAIF model [Feth, Pere. & Psychoph., lQ., 375-378 (1974) ] can account for the obtained data. For (partially) resolved signals. a two-channel model [ Durlach, Braida and Ito. J. Acoust. Soc. Am. 80, 63-72 (1986) ] is able to model the data. The values of certain model parameters show that the auditory system does not always process the changes optimally, in the sense that amplitude changes in one component contribute more in the detection process than those in the other component. This is especially true for large frequency separations. The values of some other model parameters are more difficult to interpret, but suggest that central noise is involved.