Online research in philosophy

According to Pylyshyn, the early visual system is able to categorize perceptual inputs into shape classes based on visual similarity criteria; it is also suggested that written words may be categorized within early vision. This speculation is contradicted by the fact that visually unrelated exemplars of a given letter (e.g., a/A) or word (e.g., read/READ) map onto common visual categories.

This commentary focuses on shape constancy in vision and its relation to sensorimotor knowledge. I contrast “Protean” and “Constancian” views about how to describe perspectival changes in the appearance of an object’s shape. For the Protean, these amount to changes in apparent shape; for Constance, things are not merely judged, but literally appear constant in shape. I give reasons in favor of the latter view, and argue that Noë’s attempt to combine aspects of both views in a “dual aspect” account does not manage to avoid an unacceptable attribution of contradictory content to visual appearance. I argue also that my position here actually fits better with Noë’s critique of a “snapshot” conception of visual appearance than his own interpretation of visual constancy, and better supports his claim that experiential content is constituted by the exercise of sensorimotor understanding.

Visual objects can be represented by their similarities to a small number of reference shapes or prototypes. This method yields low-dimensional (and therefore computationally tractable) representations, which support both the recognition of familiar shapes and the categorization of novel ones. In this note, we show how such representations can be used in a variety of tasks involving novel objects: viewpoint-invariant recognition, recovery of a canonical view, estimation of pose, and prediction of an arbitrary view. The unifying principle in all these cases is the representation of the view space of the novel object as an interpolation of the view spaces of the reference shapes.

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.’.

This article defends the claim that a significant part of visual perception (called “early vision”) is impervious to the influence of beliefs, expectations or knowledge. We examine a wide range of empirical evidence that has been cited in support of the continuity of vision and cognition and argue that the evidence either shows within- vision top-down effects, or else the extra-visual effects that are demonstrated occur before the operation of the autonomous early vision system (through the allocation of focal attention) or after the visual system has produced its 3D shape-description (through the intervention of post-visual decision processes).

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.

The human visual system is capable of learning both abstract and specific mappings to underlie shape recognition. How could dissimilar shapes be mapped to the same location in visual representation space, yet similar shapes be mapped to different locations? Without fundamental changes, Chorus, like other single-system models, could not accomplish both mappings in a manner that accounts for recent evidence.

Research in expert categorization is consistent with the Schyns et al. claim that functional features are determined by constraints imposed by the learning history of the categorizer and the demands of the categorization task. However, the expertise work also suggests that a distinction should be drawn between the categorizer's perceptions of the constituent parts of the object and its functional features. Although experts and novices may parse a domain-specific object into the same parts, their featural interpretations of those parts may differ significantly.

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.