A Breadth-First Survey of Eye Tracking Applications <s> Visual Search <s> A new hypothesis about the role of focused attention is proposed. The feature-integration theory of attention suggests that attention must be directed serially to each stimulus in a display whenever conjunctions of more than one separable feature are needed to characterize or distinguish the possible objects presented. A number of predictions were tested in a variety of paradigms including visual search, texture segregation, identification and localization, and using both separable dimensions (shape and color) and local elements or parts of figures (lines, curves, etc. in letters) as the features to be integrated into complex wholes. The results were in general consistent with the hypothesis. They offer a new set of criteria for distinguishing separable from integral features and a new rationale for predicting which tasks will show attention limits and which will not. <s> BIB001 </s> A Breadth-First Survey of Eye Tracking Applications <s> Visual Search <s> Abstract In standard visual search experiments, subjects look for a target item among distractor items. Targets and distractors are generally presented as isolated entities on a blank background. Do theories based on results of such experiments have any application to the real world of spatially continuous stimuli where “items” are not so conveniently delineated? Experiment 1 examines search for conjunctions of color with form and with orientation in novel stimuli designed to resemble aerial views. As with artificially isolated items, conjunction search with these complex stimuli is highly efficient, holding out the promise that models of visual search based on laboratory data can be extended to real-world situations. Experiment 2 shows that some “serial” searches are made significantly less efficient when items are embedded in these specific naturalistic backgrounds. This suggests that even classic serial searches rely on some parallel processing—the processing required to locate the “items” to be serially searched. <s> BIB002 </s> A Breadth-First Survey of Eye Tracking Applications <s> Visual Search <s> Abstract Five experiments are reported in which eye movements were recorded while subjects carried out a visual search task. The aim was to investigate whether an accurate initial target directed saccade could be programmed. In Experiments 1–2, subjects moved their eyes to targets defined by colour, which were presented with seven non-targets in a circular array. Accurate saccades with short latencies were common but errors sometimes occurred and search for an “oddity” target, defined exclusively by difference in colour from a homogeneous set of distractors, was particularly error prone. In Experiment 3, occasional trials contained double targets. First saccades sometimes landed at an intermediate position between the targets. In Experiments 4 and 5, targets were presented with 15 distractors in two concentric rings of 8. Targets specified by shape could be located accurately with a single saccade. Search for a colour-shape conjunction was more difficult but targets in the inner ring were located frequency with a single saccade. The results suggest that the control of the initial eye movement during both simple and conjunction searches is through a spatially parallel process. © 1997 Elsevier Science Ltd. All rights reserved <s> BIB003 </s> A Breadth-First Survey of Eye Tracking Applications <s> Visual Search <s> Forty years ago, Enoch reported a central bias in eye movements made during visual search tasks. Here we discuss how our Guided Search 3.0 model incorporates that observation into a general account of visual search behavior. <s> BIB004 </s> A Breadth-First Survey of Eye Tracking Applications <s> Visual Search <s> The span of the effective stimulus during visual search through an unstructured alphanumeric array was investigated by using eye-contingent-display changes while the subjects searched for a target letter. In one condition, a window exposing the search array moved in synchrony with the subjects’ eye movements, and the size of the window was varied. Performance reached asymptotic levels when the window was 5°. In another condition, a foveal mask moved in synchrony with each eye movement, and the size of the mask was varied. The foveal mask conditions were much more detrimental to search behavior than the window conditions, indicating the importance of foveal vision during search. The size of the array also influenced performance, but performance reached asymptote for all array sizes tested at the same window size, and the effect of the foveal mask was the same for all array sizes. The results indicate that both acuity and difficulty of the search task influenced the span of the effective stimulus during visual search. <s> BIB005
How humans perceive the visual scene in natural or free tasks such as picture viewing can be modeled by the visual search task. This task requires the report of the presence of a target in a display. In comparison to reading, there have not been nearly as many studies dealing with visual search  . Because the nature of the search task influences eye movement behavior, any statement about visual search and eye movements needs to be qualified by the characteristics of the search task. Specifically, visual search tasks vary widely, and tasks in which eye movements have been monitored consist of at least the following: search (a) through text or textlike material, (b) with pictorial stimuli, (c) with complex arrays such as X-rays, and (d) with randomly arranged arrays of alphanumeric characters or objects. There is considerable variability in fixation time and saccade length as a function of the particular search task  . When eye movements are recorded during extended search, fixations tend to be longer than in reading. As demonstrated by  and then by Stark (1971a, 1971b) , eye tracked scanpaths strongly suggest the existence of a serial component to the picture viewing process. However, serial scanpaths do not adequately explain the brain's uncanny ability to integrate holistic representations of the visual scene from piecemeal (foveal) observations. That is, certain perceptual phenomena are left unaccounted for by scanpaths, including perception of illusory images such as the  figure or the Necker (1832) cube. While scanpaths cast doubt on a purely Gestalt view of visual perception, it would seem that some sort of holistic mechanism is at work which is not revealed by eye movements alone. Models of visual search attempt to answer this dilemma by proposing a parallel component, which works in concert with the serial counterpart exhibited by eye movements. The consensus view is that a parallel, pre-attentive stage detects four basic features: color, size, orientation, and presence and/or direction of motion   .  suggest that attention (presumably in the periphery) is captured by sudden onset stimuli, uniquely colored stimuli (to a lesser degree than sudden onset), and bright and unique stimuli. However, there is doubt in the literature whether human visual search can be described as an integration of independently processed features  . Visual search, even over natural stimuli, is at least partially deterministic, rather than completely random  . Determinism stems from either or both of two kinds: the observer's strategy determines the search pattern (as in reading), and/or the direction of the next saccade is based on information gained through peripheral vision about surrounding stimuli. Features that are likely to be fixated include edges, corners, spatially high frequency components, but not plain surfaces. Relatively few studies have addressed the relationship between eye movements and the search process  . Findlay and Gilchrist argue that the tradition in search research to pay little attention to eye movements and instead to use the concept of covert visual attention movements (redirecting attention without moving the eyes; an important component of the Feature Integration Theory of visual attention BIB001 ) is misguided. Findlay and Gilchrist demonstrate that when viewers are free to move their eyes, no additional covert attentional scanning occurs. They show that unless instructions explicitly prevent eye movements, subjects in a search task show a natural propensity to move their eyes, even in situations where it would be more efficient not to do so. Findlay and Gilchrist suggest that the reason for this preference is that, in naturally occurring search situations, eye movements form the most effective way of sampling the visual field. BIB003 recorded eye movements during tasks of a simple feature search and a color shape feature conjunction search. Findlay's work provides an impressive confirmation that search for a pre-specified color target can be carried out in parallel. When two targets are presented simultaneously in neighboring positions, the first saccade is directed towards some "center of gravity" position. Results suggest that the control of the initial eye movement during both simple and conjunction searches is through a spatially parallel process. Results from a conjunction search experiment (color and shape) are particularly relevant since this is a situation where serial scanning would be expected according to the classical search theory of BIB001 . If a rapid serial scanning with covert attention could occur before the saccade is initiated, it is not clear why incorrect saccades would occur as frequently as observed in BIB003 experiment. Moreover, Findlay argues that the data place constraints on the speed of any hypothetical serial scanning process since it would be necessary for a number of locations to be scanned before the target is located, given the accuracy obtained. Alternative accounts of the visual search process have appeared which assign much more weight to the parallel processes and avoid the postulation of rapid serial scanning (e.g., see BIB002 , BIB004 , and  ). Recently, BIB005 had viewers search through a randomly arranged array of alphanumeric characters (i.e., letters and digits) for the presence of a target letter. They used both the moving window technique and the moving mask technique. In the moving window study, search performance was equivalent for all windows at least as large as 5 • . The moving mask had a deleterious effect on search time and accuracy, indicating the importance of foveal vision during search; the larger the mask, the longer the search time. The moving window paradigm for scene perception and visual search is discussed below as an instance of gazecontingent display technology.