Bartlett viewed thinking as a high level skill exhibiting ballistic properties that he called its “point of no return”. This paper explores one aspect of cognition through the use of a simple model...

/pdf/orienting-of-attention-2bi7r8jak3.pdf

Orienting of attention

The two basic phenomena that define the problem of visual attention can be illustrated in a simple example. Consider the arrays shown in each panel of Figure 1. In a typical experiment, before the arrays were presented, subjects would be asked to report letters appearing in one color (targets, here black letters), and to disregard letters in the other color (nontargets, here white letters). The array would then be briefly flashed, and the subjects, without any opportunity for eye movements, would give their report. The display mimics our. usual cluttered visual environment: It contains one or more objects that are relevant to current behavior, along with others that are irrelevant. The first basic phenomenon is limited capacity for processing information. At any given time, only a small amount of the information available on the retina can be processed and used in the control of behavior. Subjectively, giving attention to any one target leaves less available for others. In Figure 1, the probability of reporting the target letter N is much lower with two accompa­ nying targets (Figure la) than with none (Figure Ib). The second basic phenomenon is selectivity-the ability to filter out un­ wanted information. Subjectively, one is aware of attended stimuli and largely unaware of unattended ones. Correspondingly, accuracy in identifying an attended stimulus may be independent of the number of nontargets in a display (Figure la vs Ie) (see Bundesen 1990, Duncan 1980).

Neural Mechanisms of Selective Visual Attention

Psychophysical and physiological evidence indicates that the visual system of primates and humans has evolved a specialized processing focus moving across the visual scene. This study addresses the question of how simple networks of neuron-like elements can account for a variety of phenomena associated with this shift of selective visual attention. Specifically, we propose the following: (1) A number of elementary features, such as color, orientation, direction of movement, disparity etc. are represented in parallel in different topographical maps, called the early representation. (2) There exists a selective mapping from the early topographic representation into a more central non-topographic representation, such that at any instant the central representation contains the properties of only a single location in the visual scene, the selected location. We suggest that this mapping is the principal expression of early selective visual attention. One function of selective attention is to fuse information from different maps into one coherent whole. (3) Certain selection rules determine which locations will be mapped into the central representation. The major rule, using the conspicuity of locations in the early representation, is implemented using a so-called Winner-Take-All network. Inhibiting the selected location in this network causes an automatic shift towards the next most conspicious location. Additional rules are proximity and similarity preferences. We discuss how these rules can be implemented in neuron-like networks and suggest a possible role for the extensive back-projection from the visual cortex to the LGN.

Shifts in selective visual attention: towards the underlying neural circuitry.

http://ilab.usc.edu/publications/doc/Itti_Koch00vr.pdf

A saliency-based search mechanism for overt and covert shifts of visual attention.

Components of visual orienting

A peripheral visual cue in an empty field (1) often summons head or eyes, or both, (2) improves efficiency at the cued position while attention is directed to it, even without overt movements, and (3) reduces processing efficiency at the cued position once attention is withdrawn. We have studied the time course and the effects of mid-brain and cortical damage on these components of orienting. The facilitation arises from shifts in covert attention. In cases of mid-brain degeneration due to progressive supranuclear palsy, saccadic movements were abolished, while covert orienting still occurs. However, covert orienting was found to be delayed in directions in which eye movements were most affected, suggesting a role for mid-brain pathways in covert orienting. Parietal lesions can cause massive loss in detection contralateral to the lesion. This is especially true when attention has been directed to the opposite side. These findings relate aspects of covert orienting of attention to neural control systems.

Neural systems control of spatial orienting.

A software system for image processing, HIPS, was developed for use in a UNIX environment. It includes a small set of subroutines which primarily deals with a standardized descriptive image sequence header, and an ever-growing library of image transformation tools in the form of UNIX “filters.” Programs have been developed for simple image transformations, filtering, convolution, Fourier and other transform processing, edge detection and line drawing manipulation, simulation of digital compression and transmission, noise generation, and image statistics computation. The system has the useful feature that images are self-documenting to the extent that each image as stored in the system includes a history of the transformations that have been applied to that image. Although it has been used primarily with a Grinnell image processor, the bulk of the system is machine-independent. The system has proven itself a highly flexible system, both as an interactive research tool, and for more production-oriented tasks. It is both easy to use, and quickly adapted and extended to new uses.

/pdf/hips-a-unix-based-image-processing-system-rarrwvgkfs.pdf

HIPS: A unix-based image processing system

During voluntary movements hand and eye are coordinated under the control of central attentional mechanisms. Several techniques are reviewed that serve to dissociate the usually coordinate activity of attention, eye and hand movements. Discrepancies between central expectancies and visual input produce errors that differentially affect hand and eye. Interference between directed eye movements and manual probes is used to trace both the capacity utilization and spatial distribution of attention during eye movements. Monocular bilateral stimulation is used to separate endogenous control of oculomotor responses from pathways subserving centrally controlled eye movements and consciousness. Taken as a whole, these techniques provide promising avenues for understanding the central control of coordinate movements.

Yoav Cohen

Papers

Neural systems control of spatial orienting.

HIPS: A unix-based image processing system

14 Attention and the Control of Movements

Conjunctive Continuous Performance Task (CCPT)--A Pure Measure of Sustained Attention.

Sustained concentration : passive filtering or active orienting?