 What is the shared sense in which both visible and audible individuals deserve to be called ‘objects’? Kubovy and Van Valkenburg (2001, 2003) define objecthood in terms of figure-ground segregation, which requires perceptual grouping. They propose the theory of indispensable attributes as an account of the necessary conditions on perceptual grouping (see also Kubovy 1981). Indispensable attributes for a modality are those without which perceptual numerosity is impossible. They claim that while space and time are indispensable attributes for vision (and color is not), pitch and time are indispensable attributes for auditory objects. Though they are more skeptical about whether audition parallels vision, Griffiths and Warren (2004) sympathize with a figure-ground characterization but suggest a working notion of an auditory object defined in terms of “an acoustic experience that produces a two-dimensional image with frequency and time dimensions” (Griffiths and Warren 2004, 891).