Auditory motion segregation: a limited analogy with vision

Interaural time delay (ITD) is the dominant cue to sound-source location. When one component of a complex sound changes rapidly but smoothly in ITD, it perceptually segregates from the complex. When different components were changed in ITD in succession, a recognizable melody was heard. Each note was more detectable from the transition than from a distinct ITD with respect to the complex. However, a transition relative to a coherently changing complex produced no segregation, whereas cyclic modulation of ITD, too rapid to be perceived as movement, did produce segregation. These two results suggest that the relevant cue is not movement per se but rather the lack of a well-defined ITD during the transition. Segregation largely disappeared when the transition in ITD was replaced by a temporal gap in the complex of the order of 100 ms. The effect seems similar to visual motion segregation but is best explained by the mechanism of binaural unmasking.