Purchase this article with an account.
R. S. Anderson, N. Shah, S. C. Dakin; Individual Differences in Detection and Discrimination Performance for Vanishing Optotype Letters in Foveal and Peripheral Vision. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5171.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Vanishing optotype (pseudo-high-pass) letters display the same mean luminance as their surround and thus ‘vanish’ when the resolution threshold is reached during foveal viewing. Several previous studies have found significant differences between the detection and discrimination of pairs of vanishing optotype letters when viewing peripherally, suggesting that discrimination of these optotypes may be limited by retinal sampling in the periphery. However, under the 2AFC conditions of these studies, where the degree of ‘uncertainty’ is low, it may be that, while the letter undergoes local aliasing, it remains easily discriminable from its partner. We wished to determine the differences in detection and discrimination for individual letters under conditions of higher ‘uncertainty’, i.e. with 26 alternatives, to better determine which letters display individual sampling-limited performance.
We separately measured detection and discrimination performance for 26 different computer-generated vanishing optotypes in both the fovea and at 10 degrees in the horizontal temporal retina. Thresholds were determined for each letter using an ascending method of limits where the subject had to report either the presence of stimulus contrast (for detection) or the actual name of the letter (for discrimination). Three experienced observers took part and refractive error was carefully corrected at each location for each subject before the commencement of each test.
In the fovea, with a few exceptions, thresholds for detection and resolution were closely similar for each letter and the differences in discriminability between letters were smaller than for conventional letters. However, in the periphery, for nearly all letters, the threshold for discrimination was significantly higher than for detection (p<0.01). Detection thresholds showed only moderate differences between letters but discrimination performance varied considerably from letter to letter.
Unlike in foveal vision, most ‘vanishing’ optotypes display significant differences in their detection and discrimination thresholds in peripheral vision, i.e. do not ‘vanish’ when the resolution limit is reached. The magnitude of this difference varies from letter to letter but is further evidence for the sampling limited nature of peripheral discrimination for most of these optotypes.
This PDF is available to Subscribers Only