Visual Acuity in Foveal and Peripheral Vision

 

Thirty three percent of the retina’s ganglion cells receive input from cones that are found in just 2 percent of the retina’s total area.  This pinhead sized area near the optic nerve is called the Fovea.  Foveal vision constitutes 1-2 degrees of our visual field, which equates to roughly the area covered by your thumb at arms length.

Outside of the fovea there is a dramatic decrease in the density of cone photoreceptors.  This decrease in cones is referred to as eccentricity.

Studies show that the density of cones on the retina is linked to visual resolution.  By having subjects read an eye chart while focusing on something else, we find a direct correlation between visual acuity and the density of cone photoreceptors. 

The psychologists Sekuler and Blake write:  “It is estimated that the eye would have to contain 35 million ganglion cells in order to support uniform, high acuity throughout the retina.  To accommodate this many ganglion cells, each of your eyes would have to be as large as your whole head!” (112). 

We rarely notice that our peripheral vision is low resolution because we are constantly focusing on what we want to look at with our high resolution fovea.  The muscles surrounding the eye allow us to quickly scan our 2 degrees of foveal vision to whatever area we need to view.  Because of this, we are often completely unaware of just how low resolution our peripheral vision is.

View the examples

Note: the images on this page were taken from:
Cognition and the Visual Arts, by Robert Solso, (c) MIT Press
Perception: Fourth Edition, by Skeler and Blake, (c) 2002 Mc-Graw Hill