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 withinvision 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).

Neurons in the visual cortex of monkeys respond selectively to the disparity between the images in the two eyes. Recent recordings have shown that some of the disparity-selective neurons in the primary visual cortex and the posterior parietal cortex are modulated by the distance of fixation. A population of such gain-modulated, disparity-selective neurons forms a set of basis functions of horizontal disparity and distance of fixation that can be used as an intermediate representation for computing egocentric distance. This distributed representation is consistent with psychophysical studies of human depth perception; in contrast, neurons explicitly tuned to distance are not consistent with how we perceive distance. In a population model that includes noise in the firing rates of neurons, the perceived distance is

Abstract not found

: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : xiii I Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 A. Spatial representations and sensori-motor coordination : : : : : : : : : 1 B. The posterior parietal cortex : : : : : : : : : : : : : : : : : : : : : : : 2 C. Neural code for spatial representations : : : : : : : : : : : : : : : : : : 4 1. Dynamic remapping : : : : : : : : : : : : : : : : : : : : : : : : : : 4 2. Gain modulation : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6 3. The Zipser and Andersen Network : : : : : : : : : : : : : : : : : : 6 D. Parallel vectorial representations : : : : : : : : : : : : : : : : : : : : : 9 E. Thesis Outline : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 10 1. Hierarchy in spatial representations : : : : : : : : : : : : : : : : : 10 2. A basis function approach for spatial representation : : : : : : : : 11 II Egocentric spatial representation in early vision : :...

This is the final published version of this article; it is available at:

Contents 1. The puzzle of seeing......................................1-2 1.1 Why do things look the way they do? ..................................................................................1-2 1.2 What is seeing? .................................................................................................................1-3 1.3 Does vision create a "picture" in the head?...........................................................................1-4 1.3.1 The richness of visual appearances and the poverty of visual information: Reconciling the difference ...........................................................................................1-4 1.3.2 Some reasons for thinking there may be an inner display................................................1-6 1.4 Some problems with the Internal Display Assumption: Part I: What's in the display and how does it get there?....................................................................1-10 1.4.1 How is

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.

The two cardinal features of the syndrome described by Holmes in 19181,2 are a disorder of ocular movement and a disorder of spatial orientation. The former is manifested by severe problems of ocular fixation and accommodation, such that the patient finds great difficulty in fixing his or her gaze on an object and, having done so, has even greater difficulty in moving the point of fixation to look at something else. This means, for instance, that he cannot follow a moving object with his eyes. The second feature means that the patient has difficulty in orientating objects in three-dimensional space, so that he cannot pour a glass of water without spilling it, and, as in this case, has difficulty in lifting food with a fork or spoon. It can also result in disturbance of topographical memory so that he cannot find his way around, even in familiar surroundings. Other features found in some, but not all of Holmes's original six cases include: hemiparesis, hemisensory loss, speech disorders, visual field defects, visual neglect and apraxia. CASE HISTORY