Biomedical subjects

Gregory J Zelinsky

Publications and source records attributed to Gregory J Zelinsky.

9 recordsLinked to original sources

PubMed2006

Real-world visual search is dominated by top-down guidance.

How do bottom-up and top-down guidance signals combine to guide search behavior? Observers searched for a target either with or without a preview (top-down manipulation) or a color singleton (bottom-up manipulation) among the display objects. With a preview, reaction times were faster and more initial eye movements were guided to the target; the singleton failed to attract initial saccades under these conditions. Only in the absence of a preview did subjects preferentially fixate the color singleton. We conclude that the search for realistic objects is guided primarily by top-down control. Implications for saliency map models of visual search are discussed.

Attention↗

PubMed2006

Searching for camouflaged targets: effects of target-background similarity on visual search.

Do observers search for camouflaged targets by looking through the distractors or by scrutinizing the target-similar background? In four experiments observers searched for toy targets among distractors under varying set size and target-background similarity (TBS) conditions. Manual errors and RTs increased with TBS, although search slopes did not significantly differ. Eye movement analyses revealed that the majority of fixations fell on discrete distractors rather than on the target-similar background, even under high TBS conditions. These data suggest a biased search process; salient patterns segmented from a background are preferred while more target-similar unsegmented regions of the background are relatively neglected.

Adult↗

PubMed2005

Scene context guides eye movements during visual search.

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.

Adult↗

PubMed2005

Eye movements serialize memory for objects in scenes.

A gaze-contingent short-term memory paradigm was used to obtain forgetting functions for realistic objects in scenes. Experiment 1 had observers freely view nine-item scenes. After observers' gaze left a predetermined target, they could fixate from 1-7 intervening nontargets before the scene was replaced by a spatial probe at the target location. The task was then to select the target from four alternatives. A steep recency benefit was found over the 1-2 intervening object range that declined into an above-chance prerecency asymptote over the remainder of the forgetting function. In Experiment 2, we used sequential presentation and variable delays to explore the contributions of decay and extrafoveal processes to these behaviors. We conclude that memory for objects in scenes, when serialized by fixation sequence, shows recency and prerecency effects that are similar to isolated objects presented sequentially over time. We discuss these patterns in the context of the serial order memory literature and object file theory.

Eye Movements↗

PubMed2005

Marking rejected distractors: a gaze-contingent technique for measuring memory during search.

There is a debate among search theorists as to whether search exploits a memory for rejected distractors. We addressed this question by monitoring eye movements and explicitly marking objects visited by gaze during search. If search is memoryless, markers might be used to reduce distractor reinspections and improve search efficiency, relative to a no-marking baseline. However, if search already uses distractor memory, there should be no differences between marking and no-marking conditions. In four experiments, with stimuli ranging from Os and Qs to realistic scenes, two consistent data patterns emerged: (1) Marking rejected distractors produced no systematic benefit for search efficiency, as measured by reinspections, reaction times, or errors, and (2) distractor reinspection rates were, overall, extremely low. These results suggest that search uses a memory for rejected distractors, at least in those many real-world search tasks in which gaze is free to move.

Exploratory Behavior↗

PubMed2003

Effect of parietal lobe lesions on saccade targeting and spatial memory in a naturalistic visual search task.

The eye movements of two patients with parietal lobe lesions and four normal observers were measured while they performed a visual search task with naturalistic objects. Patients were slower to perform the task than the normal observers, and the patients had more fixations per trial, longer latencies for the first saccade during the visual search, and less accurate first and second saccades to the target locations during the visual search. The increases in response times for the patients compared to the normal observers were best predicted by increases in the number of fixations. In order to investigate the effects of spatial memory on search performance, in some trials observers saw a preview of the search display. The patients appeared to have difficulty using previously viewed information, unlike normal observers who benefit from the preview. This suggests a spatial memory deficit. The patients' deficits are consistent with the hypothesis that the parietal cortex has a role in the selection of targets for saccades, in memory for target location.

Adult↗

PubMed2003

Detecting changes between real-world objects using spatiochromatic filters.

A behavioral and computational treatment of change detection is reported. The behavioral task was to judge whether a single object substitution change occurred between two "flickering" 9-object scenes. Detection performance was found to vary with the similarity of the changing objects; object changes violating orientation and category yielded the fastest and most accurate detection responses. To account for these data, the BOLAR model was developed, which uses color, orientation, and scale selective filters to compute the visual dissimilarity between the pre- and postchange objects from the behavioral study. Relating the magnitude of the BOLAR difference signals to change detection performance revealed that object pairs estimated as visually least similar were the same object pairs most easily detected by observers. The BOLAR model advances change detection theory by (1) demonstrating that the visual similarity between the change patterns can account for much of the variability in change detection behavior, and (2) providing a computational technique for quantifying these visual similarity relationships for real-world objects.

Color Perception↗

PubMed2002

Eye movements in iconic visual search.

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).

Attention↗

PubMed2002

Eye movements and scene perception: memory for things observed.

In this study, we examined the characteristics of 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.

Fixation, Ocular↗