A reexamination of the frequency discrimination of random-amplitude tones, and a test of Henning’s modified energy-detector model

Abstract

A surprising result is reported by Henning [G. B. Henning, J. Acoust. Soc. Am. 39, 336–339 (1966)]: For frequencies lower than 4000 Hz, frequency discrimination was not impaired by the introduction of random differences in level between the two tones to be discriminated in a two-interval forced-choice (2IFC) task. This result is inconsistent with a model of detection and discrimination proposed by Henning [G. B. Henning, J. Acoust. Soc. Am. 42, 1325–1334 (1967)], one of a class of models in which the observer monitors the output of a single auditory filter, as well as with excitation-pattern models of frequency discrimination. In the first experiment reported here, however, an impairment of frequency discrimination with random differences in level is found when a within-subjects experimental design is used. In a second experiment, the role of pitch-intensity relationships in an experimental situation similar to that of Henning (1966) is explored. Finally, in a third experiment, an independent test of this model, which does not involve level differences, is carried out. The results are not consistent with the single-filter model, but can be accounted for by a version of the model that incorporates two filters.