APA Dictionary of Psychology

a theory of visual attention that posits a preconceptual mechanism by which a small number of items in the visual field (usually about four) are “indexed”—that is, marked out as discrete—so that they can be accessed by higher order cognitive functions at subsequent stages of processing. The name is a contraction of fingers of instantiation: The visual indexes are proposed to aid orientation and tracking in a manner analogous to physical fingers. Also called visual indexing theory. [proposed in 1989 by Canadian cognitive scientist and philosopher Zenon W. Pylyshyn (1937–  )]