Detection of monaural signals as a function of interaural noise correlation and signal frequency.

Abstract

The effects of varying the interaural correlation for the masking noise on the detection of monaural signals between 150 Hz and 4000 Hz were investigated. A rating-scale procedure was used to obtain ROC curves, from which measures of detection (ds) and masking level differences (MLD's) were calculated. The results show that: (1) The magnitude of the advantage for binaural over monaural detection depends on the interaural correlation for the masker and the frequency of the signal; (2) the effect of signal frequency on MLD can be portrayed as a simple reduction in the interaural correlation for noise; (3) any sizeable binaural assistance in detecting monaural signals in noise of moderate intensity is confined to frequencies between 225 and 1200 Hz; (4) additive acoustic noise produced in the ear canal is not a sufficient explanation for the dramatic reduction in binaural assistance found for signals below 250 Hz; (5) the striking dependence of low-frequency MLD's on noise level suggests that the speed of propagation of the traveling wave, and the basal spread of neural excitation on the basilar membrane are the major determiners of binaural unmasking for these signals; (6) the consistent agreement of ROC curves for human observers with the appropriate theoretical curves for the degraded amplitude detector provides no evidence for believing that the stimulus distributions for binaural detection differ markedly in form from the amplitude distributions for monaural detection; and, (7) as long as care is taken in the training of observers, the Jeffress conversion from one value of ds and signal level to another is an efficient means of obtaining differences among interaural conditions.