Online research in philosophy

As color constancy is standardly conceived, perfect color constancy would involve the apparent colors of objects being completely invariant with respect to changes in illumination (and scene composition). The illuminant would not figure in the way objects look (in respect of color) and an apple or a rose would look the same color under the fluorescent lights of my office or the direct sunlight of the plaza outside. Although we might see lights, the way in which an object is illuminated would play no role in its appearance. Yet it is quite common, particularly in travel writing and writing about art to find statements like the following explanation of why there is so much brightly colored stuff in southern California: “Failing to understand that the beautiful coloring of the land is not a reflection of things, but consists in the peculiar quality of the light itself, newcomers have indulged in riotously incongruous color schemes.” (McWilliams 1973) Or to take an even more extreme claim, “The choice and composition of landscape could narrate a feeling of the locale; for the painter George Harvey all of America was definable by the peculiar quality of the light.”(Reese and Miles 1996) Now it could be that the authors are thinking of the peculiar appearance of the principle sources of light, i.e. the sun and sky, but I doubt it. They could also be noticing failures of color constancy, consistent shifts in the apparent colors of objects when viewed in the special circumstances of Los Angeles and the like. This is more plausible, but the idea that I would like to explore is the possibility that these writers are responding to the way the things they see are illuminated but not by way of a failure of color constancy. Discussion of this possibility will then lead to a consideration of different ways of understanding some of the processes that give rise to the imperfect degree of color constancy actually possessed by human color vision.

profile deforms as we move about it. As perceivers we are masters of the patterns of sensorimotor contingency that shape our perceptual interaction with the world. We expect changes in such things as apparent size, shape and color to occur as we actively explore the environment. In encountering perspective-dependent changes of this sort, we learn how things are quite apart form our particular perspective. Our possession of these skills is constitutive of our ability to see (and generally to perceive). This is confirmed by the fact that we can disrupt a person.

Philosophers have long sought to explain perceptual constancy—the fact that objects appear to remain the same color, size and shape despite changes in the illumination condition, perspective and the relative distance—in terms of a mechanism that actively categorizes variable stimuli under the same pre-formed conceptual categories. Contemporary representationalists, on the other hand, explain perceptual constancy in terms of a modular mechanism that automatically discounts variation in the visual field to represent the stable properties of objects. In this paper I argue that while the former view is unmotivated by empirical evidence, the later fails to account for inter- and intra-personal variability, the influence of expectations on constancy, and the systematic and normal failures of color constancy. A Bayesian approach that builds on the representational tradition in psychology solves both problems.

Very often, objects in the scene before us are somehow perceived to be constant or uniform or unchanging in color, shape, size, or position, even while their appearance with respect to these features somehow changes. This is a familiar and pervasive fact about perception, even if it is notoriously difficult to describe accurately let alone adequately account for. These difficulties are not unrelated—how we are inclined to describ the phenomenology of perceptual constancy will affect how we are inclined to accoun for it.

Although we find the idea of representation by similarities attractive as such, we have two main objections to the specific proposal of Edelman. First, he does not consider complexity issues in terms of storage and speed of recall for recognition. Related to this, the appearance of objects depends on far more factors than just shape, illumination, and pose. This requires an intermediate shape abstraction process that extracts category-specific shape properties from the mixed appearance of images.

Two experiments were performed to explore the mechanisms of human 3D shape perception. In Experiment 1, the subjects’ performance in a shape constancy task in the presence of several cues (edges, binocular disparity, shading and texture) was tested. The results show that edges and binocular disparity, but not shading or texture, are important in 3D shape perception. Experiment 2 tested the effect of several simplicity constraints, such as symmetry and planarity on subjects’ performance in a shape constancy task. The 3D shapes were represented by edges or vertices only. The results show that performance with or without binocular disparity is at chance level, unless the 3D shape is symmetric and/or its faces are planar. In both experiments, there was a correlation between the subjects’ performance with and without binocular disparity. Our study suggests that simplicity constraints, not depth cues, play the primary role in both monocular and binocular 3D shape perception. These results are consistent with our computational model of 3D shape recovery.

The central text of this article is Thomas Reid’s response to Berkeley’s argument for distinguishing tangible from visual shape. Reid is right to hold that shape words do not have different visual and tangible meanings. We might also perceive shape, moreover, with senses other than touch and sight. As Reid also suggests, the visual perception of shape does not require perception of hue or brightness. Contrary to treatments of the Molyneux problem by H. P. Grice and Judith Jarvis Thomson, I argue that breakdowns of a certain kind between tangible and visible shape are conceivable.

2. Invariant Sensorimotor Features ("Affordances"). To say this is not to declare oneself a Gibsonian, whatever that means. It is merely to point out that what a sensorimotor system can do is determined by what can be extracted from its motor interactions with its sensory input. If you lack sonar sensors, then your sensorimotor system cannot do what a bat's can do, at least not without the help of instruments. Light stimulation affords color vision for those of us with the right sensory apparatus, but not for those of us who are color-blind. The geometric fact that, when we move, the "shadows" cast on our retina by nearby objects move faster than the shadows of further objects means that, for those of us with normal vision, our visual input affords depth perception. From more complicated facts of projective and solid geometry it follows that a 3-dimensional shape, such as, say, a boomerang, can be recognized as being the same shape Ð and the same size Ð even though the size and shape of its shadow on our retinas changes as we move in relation to it or it moves in relation to us. Its shape is said to be invariant under these sensorimotor transformations, and our visual systems can detect and extract that invariance, and translate it into a visual constancy. So we keep seeing a boomerang of the same shape and size even though the shape and size of its retinal shadows keep changing.

In this paper, I critically assess the enactive account of visual perception recently defended by Alva Noë (2004). I argue inter alia that the enactive account falsely identifies an object’s apparent shape with its 2D perspectival shape; that it mistakenly assimilates visual shape perception and volumetric object recognition; and that it seriously misrepresents the constitutive role of bodily action in visual awareness. I argue further that noticing an object’s perspectival shape involves a hybrid experience combining both perceptual and imaginative elements – an act of what I call ‘make-perceive.’.

A coin rotating back in depth in some sense presents a changing, elliptical shape. How are we to understand such (in this case) ‘appearances of ellipticality’? How is the experiential sense of such shifting shape appearances related to the experiential sense of enduring shape definitive of perceived shape constancy? Is the experiential recovery of surface shape based on the prior (perhaps more fundamental) recovery of point or element 3D spatial locations?—or is the perception of shape a largely independent perceptual achievement? Do we gain access to enduring shape properties by first detecting and working from ‘shape appearances’? These are some of the topics taken up in this paper.