Abstract not found

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

Advances in neuroscience implicate reentrant signaling as the predominant form of communication between brain areas. This principle was used in a series of masking experiments that defy explanation by feed-forward theories. The masking occurs when a brief display of target plus mask is continued with the mask alone. Two masking processes were found: an early process affected by physical factors such as adapting luminance and a later process affected by attentional factors such as set size. This later process is called masking by object substitution, because it occurs whenever there is a mismatch between the reentrant visual representation and the ongoing lower level activity. Iterative reentrant processing was formalized in a computational model that provides an excellent fit to the data. The model provides a more comprehensive account of all forms of visual masking than do the long-held feed-forward views based on inhibitory contour interactions. From the time a stimulus first enters the eye to the time a percept emerges into consciousness, the initial stimulus has been coded at several levels in the visual system. One of the main goals in studying visual information processing is to specify the representations at each level and the temporal sequence between

A theory developed by the author to describe macroscopic neocortical interactions demonstrates that empirical values of chemical and electrical parameters of synaptic interactions establish several minima of the path-integral Lagrangian as a function of excitatory and inhibitory columnar firings. The number of possible minima, their time scales of hysteresis and probable reverberations, and their nearestneighbor columnar interactions are all consistent with well-established empirical rules of human shortterm memory. Thus, aspects of conscious experience are derived from neuronal firing patterns, using modern methods of nonlinear nonequilibrium statistical mechanics to develop realistic explicit synaptic interactions.

Abatraet-Rapid texture segregation is examined using filtered noise textures. The stimuli consist of a foreground region of filtered noise with one dominant texture orientation against a background region with a different dominant orientation. Shape discrimination of the foreground region is measured as a function of the difference in orientation between the two regions (AO), the distance over which the dominant orientation rotates from the background to the foreground value (AX), and the dominant spatial frequency of the textures (f). Pe~o~an ~ declines with smaller A@, larger Ax, and lowerf. These effects are partially independent of viewing distance, which implies that it is the refuiiue or object spatial frequency, not retinof spatial frequency, which determines performance in this task. We present a model consisting of channels tuned for orientation and spatial frequency which compute local oriented energy, followed by (texture) edge detection and a cross-correlator which performs the shape discrimination. Monte Carlo simulations of this model are in accord with the degradation in performance with increased Ax and decreased AtI Texture Texture gradient Spatial filtering

this paper (see summary in Fig 4), the "preattentive dt " tasks that result in parallel visual search seem to rely on neuronal selectivities present in early visual areas (e.g. orientation, color), while those that result in serial visual search probably rely on higher-level neuronal selectivities (color-orientation conjunctions, animals, faces). These differences in neuronal selectivities are usually accompanied by differences in the size of the neuronal receptive fields (Desimone et al, 1988). Thus we propose that the extent to which our "preattentive dt " features can be discriminated in parallel is an inverse function of the receptive field size of the neurons that represent this feature. At higher levels of the ventral hierarchy, only very few "features" can be processed in parallel, and the corresponding stimuli must be well enough separated to avoid having a target and a distractor falling within a single receptive field. This could explain why a recent study by Rousselet et al (2002) found that 2 natural scenes can be processed in parallel (in an "animal vs. non-animal" Figure 4. Summary of results and hypothesis. A. Two independent dimensions are needed to account for the variety of visual discrimination tasks: one with respect to visual search performance (the "parallel vs

To reexamine the role of covert attention in visual search, the authors directly manipulated attention by peripherally cueing the target location and analyzed its effects on the set-size and the eccentricity effects. Observers participated in feature and conjunction tasks. Experiment 1 used precues, and Experiment 2 used postcues in a yes-no task under valid-, invalid-, and neutral-cueing conditions. Experiments 3 and 4 used a 2-interval alternative forced-choice visual-search task under cued and neutral conditions. Precueing the target location improved performance in feature and conjunction searches; postcueing did not. For the cued targets, the eccentricity effect for features and conjunctions was diminished, suggesting that the attentional mechanism improves the quality of the sensory representation of the attended location. The conjunction set-size effect was reduced but not eliminated. This questions serial-search models that attribute a major role to covert attention in visual search. Visual search is one of the leading paradigms in the study of visual perception and attention. In a typical visual-search experiment, observers have to decide whether or not a target is present in a visual array containing other nonrelevant items (distractors). For some stimuli, but not for all, reaction time (RT) increases as the number of distractors increases, a phenomenon known as the set-size effect. A large number of studies that attribute this effect to limited covert attentional processes have used the visual-search paradigm to investigate the nature of attention allocation. When performance is not affected by the number of distractors, it is assumed that the array is searched in parallel, preattentively, but a performance that deteriorates as set size increases is interpreted as indicating a covert attentional serial search (e.g.,

Abstract not found

We present three types of analog VLSI circuits that can be used in manufacturing inspection systems. The first set of circuits performs an adaptive threshold of an input image. The second circuit uses morphological operations with programmable structuring elements to detect oriented edges. Both of these circuits can be used as high speed preprocessors for visual inspection of manufacturing processes. The third circuit performs a computation necessary for selective attention in visual processing. This circuit is a component of a larger system that will facilitate a serial/parallel processing scheme in order to increase the speed of processing in machine vision tasks. All circuits presented use focal-plane processing to achieve their massively parallel architectures. For each design, the processing pixels contain vertical bipolar phototransistors to accommodate parallel optical inputs. All circuits have been fabricated using a standard 2.0 m digital CMOS process. Data for each of these c...

: In this paper we present analog very large-scale integrated (VLSI) circuits that perform the selection process for attentive visual processing. These circuits use excitatory feedback in a winner-take-all computation to produce a hysteresis in the selection from one location to the next. We present several alternative forms of excitation that can be used to enhance surrounding regions of the presently attended location. Each form of excitation is discussed and experimental results from a one-dimensional array are presented. We also demonstrate the performance of these circuits within a system that receives optical inputs and outputs a single voltage that encodes the position of attention. The system demonstrates the potential use of these excitatory feedback circuits for electronic tracking of a stimulus within a noisy environment. 1. Introduction In biological vision systems, the term attention describes the way that information is prioritized and selected [1]. Selective attention i...