Search for conjunctions of highly discriminable features can be rapid or even parallel. This article explores, three possible accounts based on (a) perceptual segregation, (b) conjunction detectors, and (c) inhibition controlled separately by two or more distractor features. Search rates for conjunctions of color, size, orientation, and direction of motion correlated closely with an independent measure of perceptual segregation. However, they appeared unrelated to the physi-ology of single-unit responses. Each dimension contributed additively to conjunction search rates, suggesting that each was checked independently of the others. Unknown targets appear to be found only by serial search for each in turn. Searching through 4 sets of distractors was slower than searching through 2. The results suggest a modification of feature integration theory, in which attention is controlled not only by a unitary "window " but also by a form of feature-based inhibition. Objects in the real world vary in a large number of prop-erties, at least some of which appear to be coded by special-ized, independent channels or modules in the perceptual

Spatial attention: Visual selection and deployment over space The attentional spotlight and spatial cueing Attentional shifts, splits, and resolution Object-based Selection The visual search paradigm Top-down and bottom-up control of attention Inhibitory mechanisms of attention Invalid cueing Negative priming Inhibition of return Temporal attention: Visual selection and deployment over time Single target search Attentional blink and attentional dwell time Repetition blindness NEURAL MECHANISMS OF SELECTION Single-cell physiological method Event-related potentials Functional imaging: PET and fMRI

this article, we present a model of similarity comparison that makes specific time course predictions, which were tested in three experiments. Before turning to that model, we first outline the need for a consideration of similarity processes

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Multimedia databases (in particular image databases) are di#erent from traditional system since they cannot ignore the perceptual substratum on which the data come. There are several consequences of this fact. The most relevant for our purposes is that it is no longer possible to identify a well defined meaning of an image and, therefore, matching based on meaning is impossible. Matching should be replaced by similarity assessment and, in particular, by something close to human preattentive similarity. In this paper we propose a geometric model of similarity measurement that subsumes most of the models proposed for psychological similarity.

Authoring is the collection, selection, preparation and presentation of information to one or more readers by an author. The thesis takes a new, critical look at traditional approaches to authoring, by asking what knowledge is required and at which stages of the process. From this perspective, traditional authoring is seen to entrench an early commitment to both form and content. Although the late binding of form is now commonplace in structured document preparation systems, a similar delay in the binding of content is necessary to achieve user-tailored interaction. The authoring paradigm we have developed to service this goal is called intent-based authoring, because the author supplies at compile-time a communicative goal, or intent. Just as SGML editors and HTML browsers defer rendering decisions until run-time by referring to a local style-sheet, intent-based authoring systems defer content-selection decisions until run-time when they refer to models of both author and reader(s). T...

This document is a review of the literature of three related areas: psychophysical vision research, automatic display generation, and multi-dimensional data visualization. Common threads are explored, and a model of the visualization process is proposed which integrates aspects of these three areas. In the review of psychophysics, attempts to find a set of primitive perceptual channels are explored. In the literature on automatic generation and visualization, attempts to employ these psychophysical findings are investigated. Finally, the proposed model is a framework which might facilitate this kind of cooperation. Contents 1 Introduction 1 1.1 Motivation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 1.2 Structure of this paper : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 2 Attention, Pre-attention, and the Ranking of Perceptual Tasks 2 2.1 Psychophysics : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 2 2.1...

During a critical period of postnatal development of the mammalian visual cortex, synaptic connections are susceptible to use-dependent modifications. Synaptic connections strengthen if pre- and postsynaptic elements are active simultaneously and postsynaptic depolarization is sufficient to allow for the activation of A'-methyl-D-aspartate (NMDA)-receptor-gated conductances. By contrast, synaptic gain decreases if postsynaptic activation exceeds a critical threshold and presynaptic afferents are not capable of activating NMDAreceptor-dependent conductances. These processes lead to selective stabilization of connections between neuronal elements which often exhibit correlated activity and thus modify connectivity according to functional criteria. It is suggested that such experience-dependent selection of circuits serves different purposes at different levels of visual processing. At the input stage to the striate cortex it contributes to optimize the match between the representations of the two eyes. At a later stage of processing it participates in the development of selective connections between cortical columns and thereby serves to establish neuronal

In this paper we present our ideas on similarity based image databases, and a new type of interface that we are developing for navigation in a databse of images. The interface facilitates navigation in a display space whose geometric characteristics depend on the geometry of the perceptual space in which image similarity is measured. The display space is a subset of the three dimensional Euclidean space that, for many of the distance functions we use, is contained in the unit cube. The perceptual intuition of the metric is given in part by the distribution of images in the space and in part by making the motion of the user uniform with respect to the metric of the space. 1 Introduction In this paper we discuss several problems in trying to build image databases in which images are searched through their perceptual characteristics. These databases operate directly on the image data, and require no encoding or labeling by an operator. Working with perceptual data requires to rethink and...

Vision is a very important issue developing artificial anthropomorphic systems. Starting from traditional knowledge about ocular movements, mainly due to physiological observations, the paper revisits primary ocular processes and proposes some new ideas for oculomotor control. It is shown that using space-variant sampling, pursuit, vergence and saccadic process are considerably simplified. The concept of binocular fusion is easily implemented and becomes very important in order to segment a candidate target from the background and perform continuous tracking over time. A set of experiments on real data demonstrates that space-variant processes can be fruitfully integrated in a simple hardware platform. This research has been supported by the VAP - ESPRIT Basic Research Project. 1 Introduction Understanding how the human vision system operates is essential in order to develop anthropomorphic systems, aimed at performing as humans do, and to provide artificial machines with unforeseen...