Visual indexing theory, also known as FINST theory, is a theory of early visual perception developed by Zenon Pylyshyn in the 1980s. It proposes a pre-attentive mechanism (a ‘FINST’) whose function is to individuate salient elements of a visual scene, and track their locations across space and time. Developed in response to what Pylyshyn viewed as limitations of prominent theories of visual perception at the time, visual indexing theory is supported by several lines of empirical evidence.