Archive for February, 2009

The Eyes Have It?

February 21, 2009

As an oral deaf person I rely a great deal on my eyes.   With my eyesight, I can read lips, facial expressions, hand gestures, and body language  in communications with others.  Many d/Deaf individuals rely on their eye vision for understanding the visual language of ASL, for lipreading/cueing with aided residual hearing or without, and taking in their environment around them.  Many d/Deaf individuals depend on their eyes as a primary sense to take up what their ears don’t do very well and hence, they don’t take their eyesight for granted, the way so many hearing people do.

But ya know, there are some things our eyes don’t see.  Check out http://serendip.brynmawr.edu/bb/blindspot1.html and have some fun.

Yup, we all got our blindspots.

Try the site’s ‘More Blindspots’ tests, such as the “Switching Colors” yellow/green test and the “Lines” test.  The more, the merrier.

As you will discover, our brains make up for the blindspots.  Powerful stuff this gray matter, this brain, our consciousness.

There is a strange phenomenon called blindsight.  It’s been mentioned in a few blogs and on YouTube recently.  Scientific and medical researchers have observed this phenomenon in individuals who suffered brain damage as a result of a stroke, brain surgery or brain trauma.  Blindsight persons “see” (even with 20/20 vision in both eyes) but do not “understand” what exactly they see.  In other words, they can see but don’t have a conscious understanding of what their eyes are seeing.

Blindsight persons are known to “detect” objects as they navigate a room however, only guessing at the shape, color, or movement of an object, but they are unable to actually identify an object for what it is, say a ” bouncing basketball” or a “potted plant” or a “lit lamp”.  They will more likely identify the basketball as some round orange shape moving from left to right, the potted plant as an irregular green shape, the lamp as a round yellow shape.   Theirs is a “residual” vision, but not a conscious one, which in effect makes these persons blind in another way.

Some of you may have seen an example of partial blindsight in someone who has had a stroke for example.   A right-side stroke in the brain can sometimes cause a blindsight of the left eye, hence, the term partial blindsight.  (Right side brain stroke affects the left side of the body, and vice-versa.)  Such a person may be observed eating the food only on the right side of his plate for he can see and consciously understand that side of the plate, leaving the food on the left side of the plate untouched because his left eye doesn’t “understand” what it sees.

Researchers are uncertain about the exact mechanism that causes this blindsight phenomenon.  Some say that it is directly attributed to a damaged visual cortex within the brain that is responsible for conscious seeing.  Others say that the phenomenon is due to the brainstem that, if intact even with a damaged visual cortex, controls basic functions of the body such as the heartbeat and breathing.   The brainstem is the most primitive  part of the brain, site of functions that were critical to prehistoric man’s survival.   So, the basic functions of vision, that is, shape, color, and movement, are believed to be situated in the brainstem as well to serve as a visual alarm system before a threat registers consciously.

So, blindsight is a reminder that a great deal  happens unconsciously on the back burner before an image registers as a conscious thought.

On another note, blindsight reveals (pun intended) that humans with a damaged visual cortex can see without understanding what they see…or that they see.

Now that’s an even weirder thought.

Ann_C