Binaural Loudness Summation for Tones and Noise

Abstract

The relation between binaural and monaural loudness was measured by magnitude estimation and magnitude production for a 1000-Hz tone and for a white noise. Four types of stimuli—monaural and binaural tone, monaural and binaural noise—were presented together, at eight levels, in mixed, randomly selected sequences. Subjects were instructed to rate or adjust the four stimuli according to a single loudness scale. The loudness of the monaural and binaural tones was a power function of sound pressure with an exponent near 0.5. The loudness of the noise increased more rapidly at low levels than that of the tone; at high levels, it increased more slowly. The bow shape of the noise function would be predicted from loudness matches between wide-band and narrow-band stimuli. A binaural sound was 1.3 to 1.7 times louder than a monaural sound at the same SPL. The results of these direct loudness estimations agreed almost perfectly with earlier results from another group of subjects who made loudness matches between binaural and monaural stimuli. [Research supported by a grant from the National Institute of Neurological Diseases and Blindness.]