Sometimes we joke "we have four eyes" in Deaf world when we're asked "how do you know?" as if we could "hear" without physically hearing with ears. No, it doesn't mean the same thing in the hearing world where four eyes indicate eyes and eyeglasses. We mean our two eyes on the front and other two eyes on the back.
Deaf people's eyesight is as sharper as an eagle's, is widely peripheral like an iguana, is as alert as a housefly, and has faster saccadic movements.
"[Deaf people] are first, last, and all the time the people of the eyes" -- George Veditz, 1910.
Studies show a very interesting fact that the region of the brain used for hearing is not wasted nor is left unused in Deaf people. This 'hearing' plasticity of the brain is used as visual and tactile.
"Using congenitally deaf cats and hearing cats, Lomber and his team showed that only two specific visual abilities are enhanced in the deaf: visual localization in the peripheral field and visual motion detection. They found the part of the auditory cortex that would normally pick up peripheral sound enhanced peripheral vision, leading the researchers to conclude the function stays the same but switches from auditory to visual." -- Science News.
Many Deaf people describe their experience, observing how often hearing people overlook happenings or things to the point of nearly being blind. That is, seeing without looking.
Cartoon by Matt and Kay Dangle, www.thatdeafguy.com
Both individual observations and studies show that Deaf people's eyesight is sharper and has larger peripheral vision.
Something catching my attention was that my highly-visual hearing daughter, who has been exposed to native ASL (American Sign Language) as a first language since birth, demonstrated her well-developed peripheral vision as early as age one. She responded without looking at me signing from time to time.
It's not uncommon that Deaf people listened to other ASL speakers out of peripheral vision. For example, a signer was talking in ASL while I was listening out of peripheral vision while I was busy attending to my toddler.
Deaf people have known it for thousands of years.
"We already know that, but pah, a science admits it. :)" -- Kevin Gamache (FB).
Note that "pah" is a gloss for the ASL sign for "finally".
Standing on the top of the blocks, we (back then novice swimmers) awaited the sound of a start pistol. A few teenage teammates used to mock me being for the slowest starter. Couldn't help it that I had to watch the other swimmers and followed them.
Over a few years, I climbed to the higher competitions, I was thrilled to learn that they had a light strobe that flashed whenever the pistol fired. Then, we all were equal in competition.
At the sound of the pistol, the light strobe flashed. I jumped off the block. To everyone's surprise including myself, I responded to the cue the fastest. Not only Deaf people may have sharper eyesight but also are more alert and responsive. Deaf people are not only visual but also tactile.
How about driving? Deaf drivers are known for safer drivers.
A study of the University of Sheffield shows that the retina of deaf-born adults develops differently compared to hearing adults' retinas. In addition to visual cortex, the retinas change to more advantages.
"How the Deaf Have Super Vision: Cat Study Points to Brain Reorganization." Science News. October 11, 2010. http://www.sciencedaily.com/releases/2010/10/101010133604.htm
"Deaf Adults See Better Than Hearing People, New Study Finds." Science News. November 11, 2010. http://www.sciencedaily.com/releases/2010/11/101110205051.htm
Bauman, H-Dirksen. Open Your Eyes: Deaf Studies Talking. "Upon the Formation of a Visual Variety of the Human Race" by Benjamin Bahan, pp pp 83-99.
"Retina holds the key to better vision in deaf people." Science Daily, June 2, 2011. https://www.sciencedaily.com/releases/2011/06/110601171620.htm
Related posts: vision of the Deaf people.