Differences of Interaural Phase and Level in Detection and Lateralization

By employing the same narrow band of noise (50 Hz wide, centered at 500 Hz) as both masker and signal, and by introducing a phase-shifting network between the masking and signal channels, it is possible to control the phase angle, α, between the two. For a given signal-to-noise ratio, controlling the phase angle, α, controls the relative magnitudes of the interaural phase (time) difference and the interaural difference in level between the stimuli at the two ears. When α lies between 0° and 90° and the signal is reversed at one ear relative to the other (N0Sπ), the interaural time difference and the interaural level difference favor the same ear. However, when α is between 90° and 180°, the ear that leads in phase or time will receive the weaker stimulus, thus putting time and intensity into opposition as cues to the lateralization of the stimulus. Data on both detection and lateralization were obtained using the single-interval forced-choice procedure. Large masking-level differences were found at all values of α, and good detection was exhibited even at those values of α where time and intensity were in opposition, and where performance in lateralization was very poor. Substantial individual differences in the relative importance of time and intensity as cues were found among the subjects.