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

Abstract

Purpose: Letter resolution depends on three factors: perceivability, response bias, and similarity. The aim of the present study was to investigate the effect of response bias (the sensory-independent factor) on resolution thresholds of Sloan letters in central and paracentral vision. Methods: Nine subjects with normal ocular health were recruited for this study. Using the method of constant stimuli, individual Sloan letters resolution thresholds were measured at 0° (central) and at ±3° eccentricity along the vertical meridian of the visual field. Response biases and letter similarities were computed using Luce's choice model. Results: Results showed that the differences in resolution thresholds of individual Sloan letters were significant at the central (F (9, 80) =5.02, p<.001), the upper (X2 (9) = 50.38, p<.05) and the lower (X2 (9) = 56.32, p<.05) visual field locations. Unlike letter similarity measures, response biases showed significant correlations to the differences in thresholds at the central (r = -0.83, p<.05), the upper (r = -0.73, p<.05) and the lower (r = -0.70, p<.05) visual field locations. Conclusions: Our findings suggest that response biases have a significant effect on resolution of Sloan letters that could result in overestimating resolution acuity in central and paracentral visual field locations.