The gaze movements accompanying target localization were examined via human observers and a computational model (Target Acquisition Model, TAM). Search contexts ranged from fully realistic scenes, to toys in a crib, to Os and Qs, and manipulations included set size, target eccentricity, and target-distractor similarity. Observers and the model always previewed the same targets and searched the identical displays. Behavioral and simulated eye movements were analyzed for acquisition accuracy, efficiency, and target guidance. TAM's behavior generally fell within the behavioral mean's 95% confidence interval for all measures in each experiment/condition. This agreement suggests that a fixed-parameter model using spatio-chromatic filters and a simulated retina, when driven by the correct visual routines, can be a good general purpose predictor of human target acquisition behavior.

No abstract

How does scene context guide search behavior to likely target locations? We had observers search for scene-constrained and scene-unconstrained targets, and found that scene-constrained targets were detected faster and with fewer eye movements. Observers also directed more initial saccades to target-consistent scene regions and devoted more time to searching these regions. However, final checking fixations on target-inconsistent regions were common in target-absent trials, suggesting that scene context does not strictly confine search to likely target locations. We interpret these data as evidence for a rapid top-down biasing of search behavior by scene context to the target-consistent regions of a scene.

Previous research has shown that when searching for a color singleton, top-down control cannot prevent attentional capture by an abrupt visual onset. The present research addressed whether a task-irrelevant abrupt onset would affect eye movement behavior when searching for a color singleton. Results show that in many instances the eye moved in the direction of the task-irrelevant abrupt onset. There was evidence that top-down control could neither entirely prevent attentional capture by visual onsets nor prevent the eye from starting to move in the direction of the onset. Results suggest parallel programming of 2 saccades: 1 voluntary goal-directed eye movement toward the color singleton target and 1 stimulus-driven eye movement reflexively elicited by the abrupt onset. A neurophysiologically plausible model that can account for the current findings is discussed.

Visual cognition depends critically on the moment-to-moment orientation of gaze. To change the gaze to a new location in space, that location must be computed and used by the oculomotor system. One of the most common sources of information for this computation is the visual appearance of an object. A crucial question is: How is the appearance information contained in the photometric array is converted into a target position? This paper proposes a such a model that accomplishes this calculation. The model uses iconic scene representations derived from oriented spatiochromatic filters at multiple scales. Visual search for a target object proceeds in a coarse-to-fine fashion with the target's largest scale filter responses being compared first. Task-relevant target locations are represented as saliency maps which are used to program eye movements. A central feature of the model is that it separates the targeting process, which changes gaze, from the decision process, which extracts information at or near the new gaze point to guide behavior. The model provides a detailed explanation for center-of-gravity saccades that have been observed in many previous experiments. In addition, the model's targeting performance has been compared with the eye movements of human subjects under identical conditions in natural visual search tasks. The results show good agreement both quantitatively (the search paths are strikingly similar) and qualitatively (the fixations of false targets are comparable).

In this study, we examined the characteristicsof on-line scene representations, using a partial-report procedure. Subjects inspected a simple scene containing seven objects for 1, 3, 5, 9, or 15 fixations; shortly after scene offset, a marker cued one scene location for report. Consistent with previous research, the results indicated that scene representations are relatively sparse; even after 15 fixations on a scene, the subjects remembered the position/identity pairings for only about 78% of the objects in the scene, or the equivalent of about five objects-worth of information. Report of the last three objects that were foveated and of the object about to be foveated was very accurate, however, suggesting that recently attended information in a scene is represented quite well. Information about the scene appeared to accumulate over multiple fixations, but the capacity of the on-line scene representation appeared to be limited to about five items. Implications for recent theories of scene representation are discussed.

Visual search studies typically assume the availability of precise target information to guide search, often a picture of the exact target. However, search targets in the real world are often defined categorically and with varying degrees of visual specificity. In five target preview conditions we manipulated the availability of target visual information in a search task for common real-world objects. Previews were: a picture of the target, an abstract textual description of the target, a precise textual description, an abstract + colour textual description, or a precise + colour textual description. Guidance generally increased as information was added to the target preview. We conclude that the information used for search guidance need not be limited to a picture of the target. Although generally less precise, to the extent that visual information can be extracted from a target label and loaded into working memory, this information too can be used to guide search.

To determine whether categorical search is guided we had subjects search for teddy bear targets either with a target preview (specific condition) or without (categorical condition). Distractors were random realistic objects. Although subjects searched longer and made more eye movements in the categorical condition, targets were fixated far sooner than was expected by chance. By varying target repetition we also determined that this categorical guidance was not due to guidance from specific previously viewed targets. We conclude that search is guided to categorically-defined targets, and that this guidance uses a categorical model composed of features common to the target class.