Perceptual Segregation

Most of us take for granted our ability to see the world around us. Rarely do we take time to consider the remarkable accomplishments our visual system must achieve in order to deliver a highly organized and meaningful representation of the world for the purposes of navigating, manipulating, and understanding our environment. For instance, our visual system seems to effortlessly, and instantly, present us with a beautifully structured world that is composed of distinct objects located in three-dimensional (3-D) space from what is actually a sparse sampling of light projected onto the two-dimensional (2-D) surface on the back of our eyes. Appearances aside, however, visual experience is a highly constructive phenomenon that involves dynamic interaction between the visual stimulus and brain structures on a moment-to-moment basis. The fact that we are able to see a single tree in a forest, even though it shares a vast number of similarities with its neighbors, or that we experience a floating red balloon as a single entity rather than as a collection of separate red, round, and moving features, underscores the complexities that must be overcome.

Perceptual segregation reflects the cognitive ability to separate features belonging to the same real-world entity, the grouping of these features into mutually exclusive areas, and their separation from other incompatible features in a manner that promotes a biologically useful representation of the scene. These processes are usually considered to proceed automatically, preceding attentional allocation, and represent the first stages in a hierarchy in which the perceptual system defines parts and objects, prior to imparting meaning to a scene. Although similarities exist between our sensory mechanisms and other physical systems, such as the analogous optical properties of a camera and the eye, the similarities end there, underscoring the profound and substantial transformations that occur in our sensory systems. This entry reviews contemporary theories regarding the role of segregation in visual perceptual organization and the brain mechanisms that are believed to support these abilities. Analogous auditory segmentation processes are discussed briefly at the end and in separate entries on auditory scene analysis and speech perception.