Effects of foveal and eccentric viewing on the resolution and contrast thresholds of individual letters.

Abstract

Letter recognition is regularly assessed in clinical and experimental settings using a set of letters, either with single letters that are presented successively or with a string of letters that is presented within a single trial. The aim of the present study was to determine resolution thresholds and contrast thresholds for the recognition of each of 7 Sheridan−Gardiner letters that were presented at the central fovea and different retinal eccentricities. Using a method of constant stimuli with a 7-alternative forced-choice paradigm, we measured resolution thresholds for high-contrast letters and contrast thresholds for fixed-sized letters. Measurements were made at the central fovea and at 0.5, 1.0, 2.0, and 4.0° in the lower visual field. Results indicated that the resolution threshold for high-contrast letters (in logMAR) increased approximately linearly with increasing eccentricity (slope = .13, SD = .01). Separate analyses for each letter revealed that their resolution thresholds at a particular eccentricity differed by up to .43 logMAR. However, contrast thresholds for individual letters, scaled for eccentricity, for all retinal locations tested did not differ significantly. Our findings have implications in clinical settings where measurements of visual acuity are performed with a limited number of letters, but they complement the use of low-contrast charts for measurements of contrast sensitivity for letter recognition in the periphery.

The effect of response biases on resolution thresholds of Sloan letters in central and paracentral vision

“…These results are similar to those reported previously. Figure 5 shows the slope of the regression line of letter resolution log thresholds as a function of eccentricity for two previous studies (Ludvigh, 1941;Hairol, 2015) and the current one. A direct comparison of the regression lines of two previous studies and the current one shows a similar slope, but higher thresholds ( Figure 5).…”

“…The higher thresholds in this study could be the result of differences in study design. For example, Hairol et al (2015) used Sheridan Gardiner letters and unlimited viewing time, and Ludvigh (1941) used F, E, C, L, T letters and did not specify the viewing time. Resolution threshold in log visual angle Ludvigh 1941Hairol et al 2015Current study et al, 2018.…”

“…For example, Hairol et al (2015) used Sheridan Gardiner letters and unlimited viewing time, and Ludvigh (1941) used F, E, C, L, T letters and did not specify the viewing time. Resolution threshold in log visual angle Ludvigh 1941Hairol et al 2015Current study et al, 2018. Figure 6 shows the resolution thresholds of individual Sloan letters (central) compared to two previous studies (Hamm, 2018;Reich & Bedell, 2000).…”

“…However, little is known about the effect of response biases on the resolution thresholds of individual Sloan letters. In this study, the aim was to investigate the effect of the response biases on resolution thresholds of individual Sloan letters in central and paracentral locations since the pattern of differences in letter thresholds has been found to be different at the central and paracentral locations (Ludvigh, 1941;Strasburger, Rentschler et al, 2011;Hairol, Abd-Latif et al, 2015).…”

Perbandingan Zon Interaksi Ruang Dua Dimensi Subjek Normal dan Ambliopia Anisometropik

“…Apabila sesuatu rangsangan dikelilingi oleh objek yang lain, kebolehan seseorang untuk mengenal pasti objek tersebut merosot. Kesan ini berlaku untuk pelbagai jenis rangsangan seperti huruf, nombor dan gratings (Bouma 1970;Hairol et al 2015Hairol et al , 2013Strasburger et al 1991;Stuart & Burian 1962). Kesan kesesakan boleh bertambah dengan meningkatkan jumlah objek yang mengelilingi rangsangan tersebut (Felisberti et al 2005) dan kedudukan (esentrisiti) rangsangan yang menjauhi retina (Bouma 1970;Jacobs 1979) atau pun dengan mengurangkan jarak antara rangsangan dengan objek yang mengelilinginya (Flom et al 1963).…”