In A Nutshell
Those who are totally blind have no visual perception of light or shapes, and their eyes lack workable photoreceptor cells. Nevertheless, some blind individuals can still “see” what’s around them by using echolocation and translating sounds into images in their minds. Also, even when an eye is technically blind, it can still detect blue light, which helps regulate the body’s circadian rhythm.
The Whole Bushel
One important thing we know from optical illusions is that vision happens more in the brain than in the eyes. Essentially, our eyes are simply tools for gathering data that our brains translate into some sort of image. Occasionally, the brain interprets things inaccurately (much to the chagrin of everyone who swore the dress was white and gold). The point is, the things we’re seeing are actually images created by our brain. And it’s this fact that explains why some blind people can actually see. At least, in a way.
Take, for example, Daniel Kish. As we’ve discussed before, he’s a blind man who taught himself how to navigate the world through echolocation. He makes clicking sounds with his tongue and then senses how those sound waves reflect off objects to get an idea of what’s around him. But what’s even more remarkable than him using this skill to successfully ride a bike down a street or hike up a mountain is that he’s not merely relying on hearing to get around: His brain is using echolocation to actually create images in his mind. In other words, he’s effectively seeing through sound. Naturally, his “vision” isn’t as clear or precise as a true seeing person, but scientists have compared it to the peripheral vision of sighted individuals, which is pretty impressive considering most of us assume blind folks only see blackness in their minds’ eye.
What’s more, blind people—even those completely sightless—also have the ability to perceive some light nonvisually. This was first discovered by a Harvard graduate student, Clyde Keeler, who noticed that the blind mice he was studying reacted to light. Even though their eyes lacked all photoreceptors, their pupils would shrink when exposed to light and their bodies’ circadian rhythms were also affected by light.
Later, similar results were found with people when researchers found that blind subjects could determine, at rates far higher than chance, whether a blue light was turned on or off. Also, like sighted people, blue light exposure triggered heightened alertness and executive function in blind individuals and influenced their sleep/wake cycles.
This nonvisual seeing is possible because the eye has intrinsically photosensitive retinal ganglion cells (ipRGCs) that send signals to the brain. But instead of using those signals to process images, the brain uses them to regulate things like sleep. So, although the completely blind aren’t truly capable of visualizing light, in a way their eyes can still “see” it and use it to regulate the body.
It’s these types of discoveries that are changing what we believe about seeing and blindness and proving that the blind aren’t quite as sightless as we previously thought.