Asymmetrical color filling-in from the nasal to the temporal side of the blind spot.

Hui Li,Yiliang Lu,Lothar Spillmann,Wei Wang,Janis Kan,Junxiang Luo

doi:10.3389/fnhum.2014.00534

Abstract

The physiological blind spot, corresponding to the optic disk in the retina, is a relatively large (6 × 8°) area in the visual field that receives no retinal input. However, we rarely notice the existence of it in daily life. This is because the blind spot fills in with the brightness, color, texture, and motion of the surround. The study of filling-in enables us to better understand the creative nature of the visual system, which generates perceptual information where there is none. Is there any retinotopic rule in the color filling-in of the blind spot? To find out, we used mono-colored and bi-colored annuli hugging the boundary of the blind spot. We found that mono-colored annuli filled in the blind spot uniformly. By contrast, bi-colored annuli, where one half had a given color, while the other half had a different one, filled in the blind spot asymmetrically. Specifically, the color surrounding the nasal half typically filled in about 75% of the blind spot area, whereas the color surrounding the temporal half filled in only about 25%. This asymmetry was dependent on the relative size of the half rings, but not the two colors used, and was absent when the bi-colored annulus was rotated by 90°. Here, the two colors on the upper and lower sides of the blind spot filled in the enclosed area equally. These results suggest that the strength of filling-in decreases with distance from the fovea consistent with the decrease of the cortical magnification factor.

Highlights

The optic disk of the eye is formed by the ganglion cell axons exiting the eyeball on their way to the brain, resulting in a region on the retina where there are no photoreceptors and there should be no vision at all
The blind spot has been revealed by retinotopic mapping of the human primary visual cortex (V1) (Tootell et al, 1998; Awater et al, 2005), we never experience a dark hole in our visual field; instead, we perceive a complete visual world
We found that the color from the nasal side predominantly filled in the blind spot, whereas the color from the temporal side filled in only a small portion

Summary

Introduction

The optic disk of the eye is formed by the ganglion cell axons exiting the eyeball on their way to the brain, resulting in a region on the retina where there are no photoreceptors and there should be no vision at all. This area is known as the physiological blind spot which is located in the temporal visual field with its center at approximately 15◦ and subtending 6 × 8◦ of visual angle (Armaly, 1969; Ramachandran, 1992b; Pessoa and De Weerd, 2003; Komatsu, 2006). Komatsu et al (2000) have shown that there is no direct retinal input to the cortical region corresponding to the blind spot, the blind spot region may become filled in by the intracortical circuitry, resulting in large receptive fields capable of interpolating retinal signals in the interest of contiguous surface and contour perception (Komatsu, 2011)

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