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It is widely accepted that there exists a region or locus of maximal resource allocation in visual perception -sometimes referred to as the spotlight of attention. We have argued that even if there is a single locus of processing, there must be multiple loci of parallel access -several places in the visual field must be indexed at once and these indexes can be used to determine where attention is allocated. We have carried out a variety of studies to support these ideas, including experiments showing that subjects can track multiple independent moving targets in a field of identical distractors, that the enhanced ability to detect changes occurring on these targets does not accrue to nontargets nor to items lying inside the convex polygon that they form (so that a zoom-lens of attention does not fit the data). We have used a visual search paradigm to show that (serial or parallel) search can be confined to a subset of indexed items and the layout of these items is of little importance. We have also studied the phenomenon known as subitizing and have shown that subitizing occurs only when items can be preattentively individuated and in those cases location precuing has little effect, compared with when counting occurs, which suggests that subitizing may be carried out by counting active indexes rather than items in the visual field. And finally we have run studies showing that a certain motion effect that is sensitive to attention can occur at multiple precued loci. We believe that this evidence suggests that there is an early preattentive stage in vision where a small number of salient items in the visual field are indexed and thereby made readily accessible for a variety of visual tasks.

The in situ optical properties and electrocatalytic performance of representative water-oxidation catalyst have been considered.

Editor:Abstract. We used cascade-correlation to model human cognitive development on a well studied psychological task, the balance scale. In balance scale experiments, the child is asked to predict the outcome of placing certain numbers of equal weights at various distances to the left or fight of a fulcrum. Both stage progressions and information salience effects have been found with children on this task. Cascade-correlation is a generative connectionist algorithm that constructs its own network topology as it learns. Cascade-correlation networks provided better fits to these human data than did previous models, whether rule-based or connectionist. The network model was used to generate a variety of novel predictions for psychological research.

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Inhibition of return (lOR) is the name that has been assigned to a response time CRT) delay to a stimulus presented at a recently stimulated spatial location. A commonly held explanation for the origins of lOR is that perceptual processing is inhibited and that this inhibition translates into slower RT. Three experiments with 10 subjects were used to directly test this perceptual explanation. The first two experiments assessed the level of perceptual facilitation present in the lOR paradigm using the frequency and latency of illusory line motion judgments. Contrary to the predictions of the perceptual view, the line motion and RT measures revealed only speeded processing at previously stimulated spatial locations. Experiment 3 required a simple detection response and used the same stimulus and timing parameters as those in Experiments 1 and 2. lOR was present, replicating the recent finding that judgments based on perceptual qualities of the stimulus do not demonstrate a RT delay, whereas simple detection tasks do show RT inhibition at previously stimulated locations. These findings are discussed in relation to a number of hypotheses about the origin of the RT delay.Inhibition of return (lOR) is a delay in responding to a target, either manually or with eye movements, at a previously stimulated visual location. The effect was first discovered by Posner and Cohen (1984), who postulated that the response time (RT) delay reflected the inhibition of attention from returning to process information at locations where visual processing had recently occurred. In the standard lOR paradigm, a first stimulus (S I) appears at one of a number of possible display positions. A second stimulus, the target, then appears either at the same location as S1 or at a different location. At short S I-target stimulus onset asynchronies (SOAs less than approximately 300 msec), subjects detect the target faster when it appears at the same location as S1. After 200-300 msec, targets at S1 are detected more rapidly. lOR is observed as a delayed RT to the appearance of the target at S I relative to responses to targets at a location that was not previously stimulated.The functional significance of the proposed inhibitory process is apparent if one considers tasks such as visual search. A reflexive bias against returning attention to previously examined locations would aid organisms in more efficient processing of the visual field by decreasing the This research was supported by NSERC Canada Postgraduate funding and an Honorary Izaak Walton Killam Scholarship to the author and by NSERC Canada Operating Grant A2600 to Zenon W. Pylyshyn. The author thanks all his participants and thanks Verla Schmidt and Michael Hiemstra for assisting in data collection. Ray Klein's zeal for discussion and mastery of the topic matter have been indispensable in the presentation of this work. Pierre Jolicoeur, Art Kramer, Hermann Muller, and an anonymous reviewer contributed by making constructive comments on an earlier draft. Correspondence should be addressed t...