City Research Online

Abstract

This thesis investigates the temporal processing of visual stimuli, particularly luminance flicker, in the context of binocular vision. Prior research on monocular versus binocular thresholds has yielded conflicting results, which may be attributed to various factors such as individual variability, naso-temporal asymmetry, and spatio-temporal stimulus properties. To address this variability, we optimized stimulus parameters such as temporal frequency, eccentricity, luminance, and chromaticity to elicit rod and cone-specific responses. Three experiments were conducted to gain insights into the limits of binocular summation in temporal domain. The study investigated the roles of the absolute monocular threshold, variations in retinal illuminance between the two eyes, and differences in binocular summation.

The aim of the first experiment was to understand the flicker processing in monocular and binocular viewing under photopic and mesopic conditions. Five target sizes and two luminance conditions (photopic/mesopic) were incorporated in the experiment to induce a range of absolute monocular thresholds. The binocular summation ratios stayed unaffected by the absolute monocular thresholds, and binocular inhibition manifested solely when there were larger interocular differences, exceeding the limits of agreement for each target size. In conclusion, the study demonstrated binocular summation resulting in an enhanced flicker detection, regardless of absolute monocular thresholds.

In the second experiment, the objective was to investigate binocular flicker sensitivity by deliberately introducing different retinal illuminances between the eyes. The key finding revealed that the binocular summation ratio (the process by which the visual cortex combines information from both eyes to create a unified perceptual experience) was unchanged until the interocular difference (IOD) in retinal illuminance was 50%. IOD of 60% or greater caused binocular inhibition and monocular suppression. This negative impact on summation was comparable to disruptions observed in the spatial domain, indicating that intentional variations in retinal illuminance, encompassing factors like blur and contrast, can compromise the visual systems ability to integrate information from both eyes effectively. This insight contributes to our understanding of how specific interocular differences in retinal illuminance influence binocular vision and the integration of visual stimulus.

The third experiment established the summation ratios with IOD in Flicker modulation threshold (FMT) and region-specific changes in FMT using a disease model. The impact of interocular differences and changes in FMT on binocular summation was studied in a unilateral ocular pathology i.e, Branch retinal vein occlusion (BRVO). There was a significant increase in thresholds in the affected regions of the diseased eye. Additionally, the binocular summation ratios were also affected. This information implies that the disease in one eye has a discernible impact on both the sensitivity to visual changes and the binocular summation involving both eyes.

Overall, this thesis provides insights into the complex process of binocular summation of luminance flicker. Also, highlights the importance of increase in IOD in retinal illuminances can impact the binocular summation capabilities, may induce monocular suppression in large IODs. In addition, it is important to consider the individual variability in understanding visual processing. This also sets the operating range of the visual system for a temporally varying signal in terms of stimulus and IOD properties.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

Export

Downloads