Contour interaction for high and low contrast optotypes in normal and amblyopic observers

Contour interaction for high and low contrast optotypes in normal and amblyopic observers Summary We investigate the influence of stimulus contrast upon contour interaction in normal and amblyopic subjects. Using a computer generated acuity task, flanked and unflanked acuities were measured psychometrically at both high contrast (80%) and low contrast (6%), in a group of 19 normal and 11 amblyopic subjects. The crowding ratio for high contrast letters was found to be significantly higher than that for low contrast letters. The extent of the crowding zone was measured at high and low contrast by varying the separation of the optotype and flanking bars. The crowding zone measurement was repeated for the high contrast optotypes using dioptric blur. The position of the flanking contours was found to have a significant effect on letter resolution at high contrast but no significant effect was demonstrable at low contrast. With the addition of dioptric blur the effect of contour interaction became negligible at high contrast. These findings support the hypothesis that the crowding effect is: (1) similar in normal and amblyopic eyes when tested at threshold; (2) is contrast dependent appearing only for high contrast optotypes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ophthalmic and Physiological Optics Wiley

Contour interaction for high and low contrast optotypes in normal and amblyopic observers

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Publisher
Wiley
Copyright
Copyright © 1999 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0275-5408
eISSN
1475-1313
DOI
10.1046/j.1475-1313.1999.00416.x
Publisher site
See Article on Publisher Site

Abstract

Summary We investigate the influence of stimulus contrast upon contour interaction in normal and amblyopic subjects. Using a computer generated acuity task, flanked and unflanked acuities were measured psychometrically at both high contrast (80%) and low contrast (6%), in a group of 19 normal and 11 amblyopic subjects. The crowding ratio for high contrast letters was found to be significantly higher than that for low contrast letters. The extent of the crowding zone was measured at high and low contrast by varying the separation of the optotype and flanking bars. The crowding zone measurement was repeated for the high contrast optotypes using dioptric blur. The position of the flanking contours was found to have a significant effect on letter resolution at high contrast but no significant effect was demonstrable at low contrast. With the addition of dioptric blur the effect of contour interaction became negligible at high contrast. These findings support the hypothesis that the crowding effect is: (1) similar in normal and amblyopic eyes when tested at threshold; (2) is contrast dependent appearing only for high contrast optotypes.

Journal

Ophthalmic and Physiological OpticsWiley

Published: May 1, 1999

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