Discriminations of interaural phase differences

Abstract

Listeners were asked to discriminate between two pulsed sinusoids, one presented with an interaural phase delay θ and the other presented with a longer delay θ + Δθ. Frequency of the sinusoids ranged from 250 to 4000 Hz. The difference threshold for Δθ was defined as the dependent variable. This threshold increased as θ increased from zero degrees to half the period of the sinusoid, then decreased as θ was further increased to a full period of the sinusoid. As θ was increased to half the period of the sinusoid, the lateral image appeared to shift away from midline toward the ear leading in time; but as θ was increased beyond half a period of the sinusoid, the lateral image appeared to shift toward the midline from the ear lagging in time. These results were obtained at 250, 500, and 900 Hz. At 2000 Hz, the value of Δθ remained a constant as θ was varied, while at 4000 Hz the lateral image was not moved by any interaural delay. The results imply that (1) for frequencies less than 2000 Hz, lateral discriminations based on interaural phase differences are more acute toward midline than at either side, and (2) for frequencies greater than 2000 Hz, changes in interaural phase are unable to shift the lateral image.