The influence of stimulus envelope and fine structure on the binaural masking level difference.

Abstract

A masking level difference (MLD) paradigm was used to investigate the influence of stimulus envelope and stimulus fine-structure characteristics on monaural and binaural hearing. The degree of masker envelope fluctuation was manipulated by selecting narrow-band noises (50 Hz) on a continuum of values of the normalized fourth moment of the envelope. The noises were specified as low-noise noise (LNN), medium-noise noise (MNN), and high-noise noise (HNN). Fine-structure cues were studied by measuring thresholds at 500 and 4000 Hz, regions in which the availability of such cues to the auditory system differ substantially. In addition, thresholds were measured for Gaussian noise maskers (GN) and for maskers having a flat magnitude spectrum, termed equal-magnitude noise (EMN) maskers. The results indicated lower NoSo thresholds for LNN than for the other four masker types. Furthermore, there were no differences in threshold for maskers having moderate and high degrees of envelope fluctuation (MNN and HNN). The NoS pi thresholds were not significantly different across masker type and were characterized by large individual differences among the seven listeners. The results are considered in relation to models of monaural and binaural processing. Consistent with previous reports, the results indicate that binaural detection depends on interaural differences in the stimulus envelope and fine structure at low frequencies and changes in the envelope at high frequencies.