To what extent does successful search for a target letter in a visual display depend on the allocation of attention to the target's spatial position? To investigate this question, we required subjects to discriminate the orientation of a briefly flashed U-shaped form while searching for a target letter. Performance operating characteristics (POCs) were derived by varying the relative amounts of attention subjects were to devote to each task. Extensive tradeoffs in performance were observed when the orientation form and target letter occurred in nonadjacent display positions. In contrast, the tradeoff was much more restricted when the two targets occurred in adjacent positions. These results suggest that the interference between simultaneous visual discriminations depends critically on their separation in visual space. Both visual search and form discrimination require a common limited-capacity visual resource.This paper is concerned with the question of whether successful detection of a target letter in a visual array of letters depends on the allocation of attention to the spatial region containing the target. We introduce a method for measuring the location of a subject's visual attention and show that allocation of attention to visual targets is a component of the search process. Correct target detections are associated with allocation of attention to the spatial region containing the target, whereas incorrect target detections are associated with allocation of attention to nontarget areas. Spatial Selective AttentionAcquisition of information from text or pictures requires a series of saccadic eye movements in which the fovea is brought to bear on different parts of the input to provide high resolution processing of local details. A similar mechanism appears to operate within a single fixation; observers can use an attentional mechanism to selectively "scan" different regions of the input. For example, if one fixates a point on this page, such as the preceding period, one can selectively "read" different letters in the area surrounding fixation. This is a central attentional process that we will refer to as spatial selective attention.Although the phenomenology of spatial selectivity is compelling, its role in visual information processing is unclear. Consider the case of visual search for

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In recognition tests, physical and semantic relationships between targets and distractors have been shown, in separate manipulations, to affect the latency of subject's decision. Recognition was tested~or distractors which were visually similar or dissimilar to targets and which belonged to the target categories or to nontarget categories in order to examine the interaction of these dimensions. Rejection latency was longer for target category than for nontarget category distractors. Latency was also longer for visually similar than visually dissimilar distractors, but only when combined with target category probes. This interaction can be explained by the hypothesis that word recognition depends on the analysis of several dimensions of the probe stimulus, and rejection can occur before all such analyses have been completed.Recent research has indicated that the recognition latency for targets from a well-memorized list and for dlstractors depends on both the physical aspects of test words and the meaning of test words. Juola, Fischler, Wood, and Atkinson (1971) required subjects to memorize a list of 16 unrelated words and then classify a series of single-word displays as containing either a memorized word, target, or a nonmemorized word, distractor. The set of distractors included words which were homophones of the targets and nonhomophones. Classification latency was slower to homophone distractors than to nonhomophones only if the homophones were visually similar to a target, e.g, SAIL and SALE. Items were considered dissimilar if two letters were different, e.g., CENTS or SENSE; or were different in length, e.g., SOME or SUM. JuoIa et a1. suggested that visual similarity between target and distractor might lead to confusions, longer times to identify words, and identification errors, although the effect of visual information on initial familiarity judgments was not ruled out. Later Atkinson and JuoIa (Note 1) stated that visual similarity could affect the speed with which the appropriate lexical node (repository of codes used in handling information) is accessed. In either case, the suggestion was that visual similarity had its effects in an encoding stage prior to the evaluation of the probe's familiarity. A similar effect of expectancy leading to misreading errors was reported by Neisser and Beller (1965). They found that some subjects misread a distractor as a target when searching a list of words for the target. Targets in long-term memory Thomas Duszak collected a portion of these data.

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