 Perceiving objects requires parsing a perceptual scene into distinct units that one can attend to and distinguish from each other and from a background. In vision, bounded, cohesive collections of surfaces that are extended in space and that persist through time play this role (see, e.g., Spelke 1990, Nakayama et al. 1995, Leslie et al. 1998, Scholl 2001, Matthen 2005). In audition, as in vision, multiple distinct perceptible individuals might exist simultaneously, and each might persist and survive change (see the discussion of auditory scene analysis in section  2.1 Sounds).  A critical difference, however, is that while vision’s objects are extended in space, and are individuated and recognized primarily in virtue of spatial characteristics, audible individuals are extended in time, and are perceptually individuated and recognized primarily in virtue of pitch and temporal characteristics (see, e.g., Bregman 1990, Kubovy and Van Valkenburg 2001). For instance, audible individuals have temporal edges and boundaries, and boundary elements can belong only to a single audible individual. They also are susceptible to figure-ground effects over time. One can, for instance, shift attention among continuous audible individuals that differ in pitch. Furthermore, they are susceptible to completion effects over time in much the same way that visible objects are perceptually completed in space. Seeing a single visible region to continue behind a barrier is analogous to hearing a sound stream to continue through masking noise, which may take place even when there is no corresponding signal (Bregman 1990, 28). Finally, multiple distinct, discrete audible individuals, such as the temporally bounded notes in a tune, can form audible streams that comprise a single perceptible unit. Such streams are subject to figure-ground shifts, and, like collections of surfaces, they can be attentively tracked through changes to their features and to one’s perspective. Though such complex audible individuals include sounds, they comprise temporally unified collections of sounds and silence that are analogous to spatially complex visible objects, such as tractors.