Two experiments on the spectral boundary conditions for nonlinear additivity of simultaneous masking

The present paper describes the results from two experiments which explored the spectral boundaries for the nonlinear additivity of simultaneous masking. The first experiment measured the threshold for detection of a 2-kHz tone in the presence of two 800-Hz-wide bands of noise that had varying degrees of spectral overlap with each other and the 2-kHz signal. Results revealed an abrupt transition from linear to nonlinear additivity of masking as the spectral separation between the two maskers varied from some overlap to none. The second experiment examined alternative explanations for the data. Explanations based on restricted-listening or distortion-product- detection hypotheses were not supported by the results of this experiment. These data indicate that nonlinear additivity of simultaneous masking holds for maskers that do not overlap within the critical band centered on the signal frequency. This interpretation is also consistent with a large body of data on the monaural and binaural summation (additivity) of loudness.