A sound element gets lost in perceptual competition.

Our ability to understand auditory signals depends on properly separating the mixture of sound arriving from multiple sources. Sound elements tend to belong to only one object at a time, consistent with the principle of disjoint allocation, although there are instances of duplex perception or coallocation, in which two sound objects share one sound element. Here we report an effect of "nonallocation," in which a sound element "disappears" when two ongoing objects compete for its ownership. When a target tone is presented either as one of a sequence of tones or simultaneously with a harmonic vowel complex, it is heard as part of the corresponding object. However, depending on the spatial configuration of the scene, if the target, the tones, and the vowel are all presented together, the target may not be perceived in either the tones or the vowel, even though it is not perceived as a separate entity. This finding suggests an asymmetry in the strength of the perceptual evidence required to reject vs. to include an element within the auditory foreground, a result with important implications for how we process complex auditory scenes containing ambiguous information.