Finding out about filling-in: a guide to perceptual completion for visual science and the philosophy of perception.

Visual filling-in, the way the brain completes missing perceptual information, is often misunderstood because the term is used inconsistently. This article organizes perceptual completion phenomena into a taxonomy, distinguishing boundary completion (like illusory contours) from featural completion (color, brightness, motion, texture, depth). Reviewing single-cell studies, the author argues that some forms of completion involve spatially propagating neural activity, contradicting the view that filling-in merely ignores an absence. Measurable effects of perceptual completion depend on neural signals representing a presence. The author rejects the idea of a single neural stage underlying perception (the bridge locus) and argues against representational and enactive conceptions of vision, concluding that perceptual content should be evaluated at the level of the whole person interacting with the world.

Study at a glance

Abstract

In visual science the term filling-in is used in different ways, which often leads to confusion. This target article presents a taxonomy of perceptual completion phenomena to organize and clarify theoretical and empirical discussion. Examples of boundary completion (illusory contours) and featural completion (color, brightness, motion, texture, and depth) are examined, and single-cell studies relevant to filling-in are reviewed and assessed. Filling-in issues must be understood in relation to theoretical issues about neural-perceptual isomorphism and linking propositions. Six main conclusions are drawn: (1) visual filling-in comprises a multitude of different perceptual completion phenomena; (2) certain forms of visual completion seem to involve spatially propagating neural activity (neural filling-in) and so, contrary to Dennett's (1991; 1992) recent discussion of filling-in, cannot be described as results of the brain's "ignoring an absence" or "jumping to a conclusion"; (3) in certain cases perceptual completion seems to have measurable effects that depend on neural signals representing a presence rather than ignoring an absence; (4) neural filling-in does not imply either "analytic isomorphism" or "Cartesian materialism," and thus the notion of the bridge locus--a particular neural stage that forms the immediate substrate of perceptual experience--is problematic and should be abandoned; (5) to reject the representational conception of vision in favor of an "enactive" or "animate" conception reduces the importance of filling-in as a theoretical category in the explanation of vision; and (6) the evaluation of perceptual content should not be determined by "subpersonal" considerations about internal processing, but rather by considerations about the task of vision at the level of the animal or person interacting with the world.