 O’Callaghan (2008a) proposes that both visible and audible objects are mereologically complex individuals, though their mereology differs in noteworthy respects. While vision’s objects possess a spatial mereology and are individuated and tracked in terms of spatial features, audition’s objects have a temporal mereology and are individuated and tracked in terms of both pitch and temporal characteristics. Discussion of auditory objects thus draws attention to two roles that space plays in vision. First, there is the role of space in determining the structure internal to visible objects, which facilitates identifying and recognizing visible objects. Second, space serves as the external structure among visible objects, and is critical in distinguishing objects from each other. In audition, time plays a role similar to space in vision in determining the structure internal to auditory objects. Pitch, on the other hand, serves as an external structural framework, along with space, that helps to distinguish among audible individuals.