Eyeing people: eyesight and the brain of Deaf people

Sometimes we joke "we have four eyes" in the 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 "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.

What does a unused hearing region of the brain do

In my ASL intermediate-level class, I explained (in ASL, as always, translated as) "In the hearing region of your brain, it's used for your hearing processing. In this same region, what does it do in Deaf people's brain like me who never hear nor use any hearing aids? Unused? Just a blank gray wasteland, eh?"

The students looked blank, waiting for an answer as I continued.

Interesting, studies show 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 enhanced as visual and tactile.

The students nodded with fascination as they had witnessed a living proof as some of them had taken my ASL courses from the very beginning (ASL 101/111) as well as from the other Deaf instructor. They became more aware of my visual world (but not fully aware).

"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.

Based on the cartoon, it's how hearing people perceive. What they don't think of is that Deaf people feel vibration and visual cues of a honking horn, screaming siren, and taking-off airplanes. Hearing doesn't go through the ears; it goes through the body in a different way.

Visual-spatial perception

Many Deaf people describe many of their observations of how often hearing people overlook happenings or things to the point of nearly being blind. That is, seeing without looking.

High visual discrimination

The illustration shows that in a study, "deaf signing children can discriminate faces under different conditions of spatial orientation and lighting better than hearing children."

Think in real life applications: Deaf native-signers also use faces as one of the articulators to convey linguistic information, such as topicalization, adverbial forms, conditionals, relative clauses, sentence types, intonation, and so on. They are sensitive to subtle facial differences.

Many hearing signers and even interpreters can unawarely miss some grammatical or semantic inflections and subtleties (movement, location, palm orientation, handshape, and non-manual signals) that native Deaf signers naturally grasp.

"Visual-spatial perception, memory, and mental transformations are prerequisites to grammatical processing in ASL (Emmorey and Corina, 1990...)".

Fast mental rotation

Another study tests deaf and hearing subjects on the mental rotation tasks.

The result shows that "Deaf signers did not mentally rotate imaged patterns better than non-signers; rather than finding differences in the speed of rotation per se, our results suggest that signing subjects were better able to evaluate mirror reversals." Ref

Deaf/native signers have easier comprehending ASL that involves transformation or reversal, such as describing an object, a room, or another.

Sharp kinesthetic perception

In an experiment, children were asked to write a Chinese pseudo-character each time they observed a lightpoint motion of the written Chinese pseudo-character in the air.

The result above shows a remarkable difference between hearing and Deaf children that deaf signers can detect and interpret moving light characters more accurately than hearing non-signers.

"In this experiment, ... Deaf signers (both Chinese and American) were significantly better than their hearing counterparts at perceiving the underlying segments of these pseudo-characters. Figure 2b [above] shows the contrast between first-grade Chinese hearing and deaf children on this task." (Neville, 1988)." (p 141)

Enhanced motion perception

In an EEG study on how deaf native signers perceive biological motions, Deaf signers and hearing non-signers watched both the Biological Motion point-light dispays (PLDs) which depicted everyday human actions and the Scrambled PLDs as control. The researchers computed the time-frequency responses.

The findings were:

1) "Deaf signers reported significantly less effort required for identifying coherent biological motion."

2) "Deaf native ASL signers showed theta, mu, and beta differentiation between scrambled and biological movements."

3) "These differences were seen earlier and more consistently than in hearing non-signers." Ref

The researchers conclude that "native ASL users exhibit experience-dependent neuroplasticity in the domain of biological human motion perception."

Enhanced peripheral vision

Deaf people have larger and sensitive peripheral vision based on many observations and studies. For example, it's not uncomomn that Deaf people gathered information out of peripheral vision.

Also, a study shows that literate Deaf people read faster because of the larger peripheral vision.

Based on anecdotes, observations, and statistics, Deaf drivers generally are safer. All the information used in driving is primarily visual.

Sharper alertness

Not only Deaf people may have sharper eyesight but also are more alert and responsive.

"My deaf daughter was extremely visual, like crazy visually intelligent, from day 2 of her life. Probably day 1 really, but we noticed it day 2. We didn't even know she was deaf yet, but we were shocked to notice how she took in the world, turned to look at everything, especially changes in light and also the ceilings anywhere we went. We had 4 hearing babies before her, they didn't even notice these things in early infancy at all. As early as a couple weeks old, we could tell she was identifying where we were by the particular visual features of the ceiling. She is incredibly smart and adaptive and visual." -- Jennifer Roy, a hearing mother of five children (Feb. 12, 2019, FB)

Better vision

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.

Deaf Eyes

Now, you have a better understanding and insight into the world of Deaf people's enhanced eyesight and brain. Deaf people are not only visual but also tactile which is more sensitive and enhanced as well.

In other word, Deaf gain where "Deaf contribution" which is beneficial for larger society, is part of.

Despite these heightened senses, Deaf people are not immune to carelessness or accident, because we are human, too. We can be sometimes daydreaming or be absorbed in something among a number of other factors. We may be super-eye but not superhuman. We are human just like you.

Resources

"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