Text

theses

Uncertainty regarding the position of the search target is a fundamental component of visual search. This position uncertainty can be either extrinsic (EPU)–uncertainty regarding where a stimulus might appear, or intrinsic (IPU)–uncertainty regarding the distal source of the perceived stimulus. Previous measurements indicate that IPU increases approximately linearly with retinal eccentricity and that it accounts for impaired detection and localization performance in the periphery (Michel & Geisler, 2011). Our aim in the current project was to characterize the role of IPU in overt visual search and to determine whether it is a limiting factor in search performance. Human observers completed two tasks. First, the observers completed a detection task to measure sensitivity to the target as a function of visual field position. Then, they completed a search task, which required localization of the target signal within a noisy environment. Observers were allowed to make a maximum of six fixations. To examine the effect of IPU, two different experimental conditions were created. In the “cluttered” condition, the display was tiled uniformly with feature clutter (in the form of 1/f noise) to maximize the effect of IPU. In the “uncluttered” condition, the clutter at irrelevant locations was removed to decrease the effect of IPU. The amount of EPU was also manipulated across conditions. We developed a constrained ideal searcher model, in which the searcher is limited by IPU measured for human observers. Individual ideal searchers were simulated for each human observer using the sensitivity measured in the detection task and the fixations sequences measured in the search task. Introducing IPU to the ideal searcher impaired overall overt search performance, but not uniformly. In the “uncluttered” condition, performance decreased steeply as a function of increasing EPU. However, in the “cluttered” condition, the effect of IPU dominated and performance flattened as a function of EPU. Measured performance for human searchers showed similar trends. Our findings suggest IPU as a limiting factor in overt search performance.

ETD_6765

M.S.

Includes bibliographical references

by Yelda Semizer

doi:10.7282/T3RV0QP6

ETD graduate

The author owns the copyright to this work.