Why do our eyes make short, rapid movements as we read instead of scanning the page continuously?
The last time you saw someone reading a book, you may have noticed their eyes didn't follow the line of text smoothly, but instead seemed to make little jumps across the page. These movements are called saccades, and we make them thanks to the anatomy of our eyes.
Photons
When we open a book, the process of reading begins with photons, or particles of light. Photons are reflected off of the page and enter our eyes.
At the back of our eyes are our retinas, which is where we find the light receptors, rods and cones, that translate particles of light into nerve signals, creating the images we see. The rods allow us to see in dim lighting, while the cones respond to bright light and allow us to see color and fine detail.
Fovea
But these light receptors are not evenly distributed across our retinas. The part of our eyes we use to see fine detail, and to read, is actually very limited: an angle of five degrees at the center of our field of vision.
This part of the eye, at the center of the retina, is called the fovea, from the Latin word for pit, and it is the most dense with cones.
According to scientists, the brain also adjusts the distance for each saccade according to the size of the print, so that the number of letters we take in with each movement remains constant: seven to nine. (Also according to scientists, learning how to read changes the structure of your brain.)
Because of this, a skilled reader's eyes move four or five times each second, apprehending as they go.
Thank you to T. Rowan Candy of Indiana University for reviewing this episode's script!
Sources And Further Reading:
- Deheane, Stanislas. Reading in the Brain: The Science and Evolution of a Cultural Invention. New York: Viking, 2009. Print.
- Hubel, Daniel. Eye, Brain, and Vision. Web. 1 Sept. 2017.
