The Influence of Interaural Phase on Masked Thresholds I. The Role of Interaural Time-Deviation

Abstract

When a narrow band of noise, of constant level (the signal) is masked by a wider band of noise (the masker), the amount of noise required to drown out the signal often depends significantly upon the interaural phase relations of signal and masker. Thus, more masking noise is required if the signal is 180° out of phase at the two ears than if it is in phase: provided that the masker remains in phase. The out-of-phase signal, in other words, shows an advantage in audibility. The advantage is very striking for a signal near 250 cps; and falls off progressively toward 1400 cps, above which it is small. At all frequencies between 250 and 6000 cps, the level of masking, for a signal in phase at the ears, remains relatively constant. An important property of physical stimuli that produce an audibility-advantage is an interaural phase-deviation caused by the signal. When the signal is added to a corresponding masking component, the combined pressure-wave, on the average, leads in one ear and lags in the other. The resulting phase-deviation depends upon the relative levels and phase-positions of the masking and masked components. It is maximum when these components are 90° apart. The interaural time-deviation thus produced depends also upon frequency. If the frequency is increased, the level of the masking component must be decreased in order to hold the time-deviation, associated with the different frequencies, constant. The present experiments showed that, with the out-of-phase signal, the decline in level of masking, as a function of frequency, is just such as to hold the interaural time-deviation (for the 90° position) constant at about 125 microseconds. Tonal signals tend to show a decreasing critical time-deviation with increasing frequency.

Binaural detection with narrowband and wideband reproducible noise maskers. IV. Models using interaural time, level, and envelope differences

“…For most complex stimuli with time-varying amplitudes, the modulation depth also changes over time, thus both ILD and ITD cues will contribute to the SIED cue at different points within the stimulus. The dominance of ITD over ILD in predicting binaural detection results is consistent with the studies by van der Heijden and Joris (2010) and Webster (1951).…”

“…His results show that at low SNR, listeners have significantly lower discrimination thresholds under dichotic conditions than under diotic conditions; at high SNR, listeners have similar discrimination thresholds for the two conditions. Henning further demonstrated that results from the amplitude-modulation discrimination task could be predicted using Durlach's EC model (Durlach, 1963) and the Webster-Jeffress models (Webster, 1951). The SIED cue provides an alternative explanation for results from amplitude-modulation discrimination because envelope cues are available for the modulated stimuli.…”

Interaural fluctuations and the detection of interaural incoherence. IV. The effect of compression on stimulus statistics

“…They are the cross-correlation (CC) model (Osman, 1971(Osman, , 1973, the equalization-cancellation (EC) model (Durlach, 1963), and interaural difference models (e.g., Webster, 1951;Hafter, 1971) that utilize ITDs and/or interaural level differences (ILDs) in various ways. The models, which started as essentially "black-box" models, have become more physiologically motivated over the years.…”

Binaural release from masking with single- and multi-electrode stimulation in children with cochlear implants

“…For normal-hearing (NH) listeners, binaural hearing provides advantages for speech reception in noise and for signal detection (Webster, 1951;Schubert, 1956;Carhart et al, 1967;Bronkhorst and Plomp, 1988;Lavandier and Culling, 2010). One advantage, referred to as "binaural unmasking," can be observed when one compares listeners' performance in a diotic condition in which the target has the same interaural configuration as the noise, to a dichotic condition in which the target and noise have different interaural configurations.…”