Varikuti PhD thesis final.pdf - Anglia Ruskin Research Online

Dakin, Kapoor and Tewfik, 2000; Danilova and Bondarko, 2007). The results ofthe present study show no significant effect of contour interaction between 0.2to 1.0 letter width separations and the maximum effect was at the abuttingcondition. The variation in the extent and intensity of contour interaction indifferent studies is likely to be due to the differences in the experimentalparadigms. This is because, the data of Alexander, Xie and Derlacki (1997)showed that the identification of letters was differently influenced when thepercentage correct responses were measured at near thresholds or if the letterthresholds were derived from the psychometric functions.Investigating the effect of contour interaction has mostly been addressed usingoptotypes surrounded by flanking bars (Flom, Weymouth and Kahneman, 1963;Jacobs, 1979; Hess and Jacobs, 1979; Manny, Fern and Loshin, 1987; Hess,Dakin, Kapoor and Tewfik, 2000; Liu, 2001). On the other hand, the effect ofcontour interaction has also been studied using optotypes in the form oftrigrams or arranged in linear arrays (Taylor and Brown, 1972; McGraw andWinn, 1993; Liu and Arditi, 2001). However, the linear array target introducesboth the effect of contour interaction and a potential instability in gazefixations leading to studying the effect of crowding rather than the effect ofcontour interaction. However, the stimulus used in the present study isdifferent, based on the fact that it is a SGRL chart design with letterssurrounded by the same letters. The SGRL acuity is less sensitive to any effectof gaze fixations or any attentional components and visual acuity is thereforeinfluenced by contour interaction only.110