Shape discrimination in central and peripheral vision and its potential for vision screening

Abstract

Background and aims: Radial frequency (RF) shape discrimination with small central and achromatic stimuli has been successfully used in vision monitoring tests for age related macular degeneration (AMD). This thesis aims to provide basic vision research in the peripheral visual field (VF) that can expand the versatility and sensitivity of the current tests. Methods: The research described herein used visual psychophysics to explore RF shape discrimination under different conditions in normal vision. Aspects explored included chromatic and luminance mechanisms, retinal location, size and scaling, binocular interactions and effects of simulated scotoma, concentric and eccentric presentation, and interval and spatial methods. Results: Achromatic and yellow-blue RF shape discrimination was shown to perform, although on a different level, relatively constant to up 20 and 15 degrees of the VF in concentric and eccentric presentation with red-green mechanisms performing less consistently. These observations support the feasibility of using chromatic, especially yellow-blue, stimuli at different retinal locations. Second, it was demonstrated that peripheral RF shape discrimination is limited by the spatial properties of the peripheral vision, thus it is constrained by low- level properties. However, over the resolution limit, performance is based on the proportion between the modulation and radius, which suggest scale invariance for RF patterns. This allows for direct comparisons between thresholds for stimuli of different sizes and eccentricities. No binocular summation was found in normal vision for yellow-blue and achromatic RF shape discrimination in central nor in peripheral vision. This did not preclude other binocular interactions induced by a simulated monocular scotoma, such as inhibition, facilitation, and suppression. A novel nested spatial presentation method was designed and examined. The findings showed that the method holds good feasibility for more efficient estimation of RF thresholds at different retinal locations. Conclusions: This thesis provides novel contributions to the current understanding of chromatic and peripheral RF shape discrimination, and brings practical implications for design of vision monitoring tests that utilise RF shape discrimination.