RETHINKING PERCEPTUAL ORGANIZATION - THE ROLE OF UNIFORM CONNECTEDNESS

A principle of perceptual organization, called uniform connectedness ( UC), is described, and a theoretical approach to perceptual organizati on is proposed in which this principle plays a fundamental role. The p rinciple of UC states that closed regions of homogeneous properties-su ch as lightness, chromatic color, texture, and so forth-tend to be per ceived initially as single units. We demonstrate its effects and show that they occur even when opposed by powerful grouping principles such as proximity and similarity. We argue that UC cannot be reduced to su ch grouping principles, because it is not a form of grouping at all. W e then propose a theoretical framework within which UC accounts for th e initial (or entry level) organization of the visual field into primi tive units. Classical principles of grouping operate after UC, creatin g superordinate units consisting of two or more basic-level units. Par sing processes also operate after UC, dividing basic-level units into subordinate parts. UC in the retinal image is proposed to be a necessa ry, but not a sufficient, condition for unit formation, since connecte d elements on the retina that are perceived to lie in separate depth p lanes fail to be perceived as units. This fact, together with other ev idence that the Gestalt principles of grouping are based on perceived (rather than retinal) relations, suggests that the organization of vis ual stimulation into UC objects is ultimately achieved within a relati vely late, postconstancy representation of environmental surfaces. The implications of this possibility are discussed in light of present th eories of visual perception.