A Comparison of Contour Interaction and Crowding

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dc.contributor.advisorBedell, Harold E.
dc.contributor.committeeMemberStevenson, Scott B.
dc.contributor.committeeMemberManny, Ruth E.
dc.creatorMarten-Ellis, Stephanie
dc.date.accessioned2019-05-23T14:05:52Z
dc.date.createdAugust 2018
dc.date.issued2018-08
dc.date.submittedAugust 2018
dc.date.updated2019-05-23T14:05:52Z
dc.description.abstractPurpose: The ability to correctly identify a target is significantly reduced by the presence of flanking distractors. The term “crowding” is often used to encompass a large variety of target and flanker types. A major aim of this study was to enumerate the differences between the impairment of target identification produced by flanking bars (contour interaction, “CI”) and flanking letters (crowding, “CW”). Both the magnitude and extent of CI and CW were studied in the context of foveal and peripheral viewing, for various background luminances, and in color congruent versus incongruent conditions. Methods: Subjects (n=4) viewed Sloan letters (C, D, H, K, N, O, R, S, V, Z) and were asked to identify such target. Flanking objects were placed at various distances from the target to induce CI or CW. Subjects repeated this task for a variety of target eccentricities (foveal versus 1.25, 2.5, 5.0, and 10 degrees in the inferior visual field), background luminances (photopic, mesopic, high scotopic, and low scotopic), and color-congruent (flanker and target either matched or did not match in color) conditions. Average percent correct letter identification was plotted as a function of flanker-to-target separation (in arcmin). Results: A significant interaction effect was found in all conditions. In the fovea, a change from photopic to mesopic luminance produced a significant decrease in both CI and CW. In scotopic conditions, peripheral CI also was reduced. No significant effect of color congruency was found. The extent of foveal CW and CI was approximately 5 arcmin. During peripheral viewing the extent ranged from 6-40 arcmin for CI and from 10 to greater than 40 arcmin for CW, with the extent increasing as targets were viewed further from the fovea. Conclusion: This study suggests that the use of flanking bars versus letters should not both be subsumed within the term “crowding” and that future comparisons must consider flanker type. The effects of luminance are consistent with a center-surround receptive-field neural model for CI. The results regarding flanker type and color congruency raise further questions on the role of flanker complexity and “top-down” influences on CW and CI.
dc.description.departmentOptometry, College of
dc.format.digitalOriginborn digital
dc.format.mimetypeapplication/pdf
dc.identifier.urihttps://hdl.handle.net/10657/3981
dc.language.isoeng
dc.rightsThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).
dc.subjectVision sciences
dc.subjectCrowding
dc.titleA Comparison of Contour Interaction and Crowding
dc.type.dcmiText
dc.type.genreThesis
local.embargo.lift2020-08-01
local.embargo.terms2020-08-01
thesis.degree.collegeCollege of Optometry
thesis.degree.departmentOptometry, College of
thesis.degree.disciplinePhysiological Optics and Vision Science
thesis.degree.grantorUniversity of Houston
thesis.degree.levelMasters
thesis.degree.nameMaster of Science

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