Masking-Level Differences as a Function of Interaural Disparities in Intensity of Signal and of Noise

Abstract

A marked release from masking, or masking‐level difference (MLD), results when a monaural signal is presented with perfectly correlated (in‐phase) binaural noise, N0—Sm, rather than with monaural noise, Nm—Sm. When the noise in the nonsignal ear is introduced at a lower level than that in the signal ear, a smaller MLD results. In one experiment, MLD's were determined as a function of the intensity of the noise in the nonsignal ear with the interaural conditions of N0, Nπ, and NU as parameters; for N0, there is some release from masking even when the noise in the nonsignal ear is as much as 40 dB down from that in the signal ear. The following considerations led to a second experiment. A release from masking results when a sinusoid is presented monaurally Sm rather than binaurally and in phase S0 with perfectly correlated noise N0. With N0‐S0, when the sinusoid in one ear is reduced in intensity, rather than being removed entirely, a smaller MLD than for N0‐Sm should result. Therefore, MLD's were determined as a function of the ratio of the energies of the left‐ and right‐ear sinusoids with correlated noise N0. In all experiments, the signal (500 cps, 0.25 sec) was presented to the listener in one or the other of two temporal intervals, against a background of white noise. Psychometric functions were determined for each condition, and MLD's were estimated from these functions.