Experiments are presented showing that visual search for Mueller-Lyer (ML) stimuli is based on complete configurations, rather than component segments. Segments easily detected in isolation were difficult to detect when embedded in a configuration, indicating preemption by low-level groups. This preemption—which caused stimulus components to become inaccessible to rapid search—was an all-or-nothing effect, and so could serve as a powerful test of grouping. It is shown that these effects are unlikely to be due to blurring by simple spatial filters at (...) early visual levels. It is proposed instead that they are due to more sophisticated processes that rapidly bind contour fragments into spatially-extended assemblies. These results support the view that rapid visual search cannot access the primitives formed at the earliest stages of visual processing; rather, it can access only higher-level, more ecologically-relevant structures. (shrink)

Adelson & Pentland (Chapter 11) use an engaging metaphor to illustrate their position on scene analysis: interpretations are produced by a workshop that employs a set of specialists, each concerned with a single aspect of the scene. The authors argue that it is too expensive to have a supervisor co-ordinate the specialists and that it is too expensive to let them operate independently. They then show that a careful sequencing of the specialists leads to solutions of minimum cost, at least (...) for their world of Mondrian panels. (shrink)

One of the more powerful impressions created by vision is that of a coherent, richly-detailed world where everything is present simultaneously. Indeed, this impression is so compelling that we tend to ascribe these properties not only to the external world, but to our internal representations as well. But results from several recent experiments argue against this latter ascription. For example, changes in images of real-world scenes often go unnoticed when made during a saccade, flicker, blink, or movie cut. This "change (...) blindness" provides strong evidence against the idea that our brains contain a picture-like representation of the scene that is everywhere detailed and coherent. (shrink)

This paper explores the ways in which resource limitations influence the nature of perceptual and cognitive processes. A framework is developed that allows early visual processing to be analyzed in terms of these limitations. In this approach, there is no one ``best'' system for any visual process. Rather, a spectrum of systems exists, differing in the particular trade-offs made between performance and resource requirements.

Recent work in experimental psychology and neuroscience has revealed a rather surprising architecture for early (or preattentive) perceptual processes. This paper will describe some of the surprising features of that architecture, and how they bear on recent philosophical debates about the notion of phenomenal consciousness. I will argue that the common sense idea that states of phenomenal consciousness are states of a unitary kind cannot survive confrontation with the details of how our early perceptual processing works. In particular, that architecture (...) forces us to contemplate the prospect of phenomenal consciousness being sundered in two, with states that have phenomenal character making an appearance far before the arrival of anything one could call consciousness or awareness. (shrink)

What are the relations between preattentive feature-placing and states of perceptual awareness? For the purposes of this paper, states of "perceptual awareness" are confined to the simplest possible exemplars: states in which one is aware of some aspect of the appearance of something one perceives. Subjective contours are used as an example. Early visual processing seems to employ independent, high-bandwidth, preattentive feature "channels", followed by a selective process that directs selective attention. The mechanisms that yield subjective contours are found very (...) early in this processing. An experiment by Greg Davis and Jon Driver is described; it seems to show that multiple subjective figures can be coded in these preattentive, parallel stages of visual processing. I propose that some of these preattentive states might register the very same differences that, were one aware of them, would be phenomenal differences. Some arguments pro and con on this possibility are assessed. (shrink)