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Investigative Ophthalmology & Visual Science, Vol 38, 1029-1039, Copyright © 1997 by Association for Research in Vision and Ophthalmology

ARTICLES AND REPORTS

Detection of geometric image distortions at various eccentricities

J Rovamo, P Makela, R Nasanen and D Whitaker
Department of Optometry and Vision Sciences, University of Wales, College of Cardiff, United Kingdom.

PURPOSE: Human ability to perceive spatial stimuli declines with increasing eccentricity. To study this phenomenon with natural images, the authors applied the spatial scaling method by measuring the smallest detectable amount of geometric change in a human face at several eccentricities for a series of stimulus magnifications to find out whether performance could be made equal across the visual field simply by an appropriate enlargement. METHODS: The authors used a novel method to produce subtle changes to an image of a face. The smallest change recognized was determined using a two-alternative forced-choice method and expressed in terms of correlation sensitivity, the inverse of the correlation between the images that just could be discriminated. RESULTS: The detection of changes in the facial features, presumably a spatially complex task, became equal across the visual field simply by an appropriate change of scale. The E2 value represents the eccentricity at which the foveal stimulus size must double to maintain performance at the foveal level. The E2 values, found to be 1.73 degrees to 2.45 degrees, were similar to our previously measured values for vernier acuity, orientation discrimination, and curvature detection and discrimination, obtained with the same method of spatial scaling. CONCLUSIONS: The authors' results indicate that with adequate stimulus magnification, one is capable of detecting geometric changes in complex images such as face equally at the fovea and in the periphery. In this task, there seems to be no qualitative difference between the accuracy of foveal and peripheral processing.


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D. R. Melmoth, H. T. Kukkonen, P. K. Mäkelä, and J. M. Rovamo
The Effect of Contrast and Size Scaling on Face Perception in Foveal and Extrafoveal Vision
Invest. Ophthalmol. Vis. Sci., August 1, 2000; 41(9): 2811 - 2819.
[Abstract] [Full Text]


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Copyright © 1997 by the Association for Research in Vision and Ophthalmology