Biomedical subjects

Gregory J Zelinsky

Publications and source records attributed to Gregory J Zelinsky.

4 recordsLinked to original sources

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↗