What do the blind see?
By Shirish Joshi

ANCIENT philosophers called the human senses "the windows of the soul," and Aristotle enumerated at least five senses — sight, hearing, smell, taste, and touch — and his influence has been so enduring that many people still speak of the five senses as if there were no others. Today we know that there are many more.

Sight is our most precious sense, and many people fear blindness more than any other disability. Eye, the organ of sight, is our most important organ for finding out about the world around us. We use our eyes in almost everything we do — reading, working, watching movies and television, playing games, and countless other activities.

The human eyeball measures only about 25 mm in diameter. Yet the eye can see objects as far away as a star and as tiny as a grain of sand. The eye can quickly adjust its focus between a distant point and a near one. It can be accurately directed toward an object even while the head is moving.

Where do we see? The eye does not actually see objects. Instead, it sees the light they reflect or give off. They eye can see in bright light and in dim light, but it cannot see in total darkness. Light rays enter the eye through transparent tissues. The eye changes the rays into electrical signals. The signals are then sent to the brain, which interprets them as visual images. We therefore, see in our brain.

What do the blind see? A blind person who has never experienced any colour like red would not have the awareness of red that the normally sighted person has. He might have some vague idea, as did the hero of the story told by a British scientist. A man born blind, who mightily beat his head about visible objects, and made use of the explanation from his books and friends, to understand those names of colours which often came in his way, said one day, that he now understood what red signified.

What was red? His friend asked. The blind man answered, "It was like the sound of a trumpet."

This reply is not totally wide off the mark; but any sighted person will have a far more precise idea of red colour than that. What he has and what the blind person lacks is something that philosophers have called the "raw feel" of red, that peculiar and special way red colour looks.

Several centuries ago, the French mathematician, Descartes, who lived from 1596 to 1650, proposed that a blind man, by tapping objects with a stick, used his sense of touch and hearing to build his mental image of the world.

Descartes believed that a normal man with eyes who tried to make out objects with a stick in a darkened room, found this kind of sensation confusing as well as blurred. He postulated that men or women who are born blind and have made use of this method of perception of objects since childhood feel things with such perfect exactness that they may be seeing with their hands and fingers.

Are the mental images of blind and sighted persons the same? As sighted people invent the language this question can not be answered easily. One blind man was asked to define a straight line. He answered,"When I have something to do immediately, I feel as if I were going forward in a straight line bound to arrive somewhere, or go on forever, without turning to the right or to the left."

Some persons born blind gain sight after surgery. They are right candidates to compare the mental images of the blind and the sighted people. A scientist studied reports from people born blind but later cured. There was a big difference in perception of these people. Another scientist asked some persons born blind to draw pictures of objects like a cup or a table on a plastic sheet that produced a raised line when a special pen is moved across it.

As we all sighted people know, any picture is a two-dimensional way of representing a three-dimensional word. Surprisingly, the blind also quickly realised this. Like us, they also chose a point of view. They also devised ways to convey this reality. What most surprised the scientist was that blind understood the principle of occlusion. While drawing the picture of a person sitting with hands crossed, they knew that part of one hand would be covered by the other.

A sighted person recognises objects and persons by matching what he sees with an earlier, formed mental image stored in the memory of his brain through his senses of sight, taste, smell and hearing. A blind person does it through his sense of touch, taste, smell, and hearing that are far more developed than an average sighted person does.

For sighted people vision is dominant, for the blind touch, taste, smell and hearing are dominant. A blind person who gains his sight after several years has to learn to see. Aman who was born blind was an expert at working on a lathe. He was shown a lathe after he gained his sight, but could not recognise it. He then closed his eyes, felt the lathe all over, and said, "Now that I have felt it, I can see."

The one who is blind can not recognise anything whose shape and texture they have not felt before, or one that does not make a sound with which they are already familiar. They recognise cars because they know the noise of the engine. They recognise persons through their voice, and items of food through taste and smell.

There have been some reports about people distinguishing colours through the sense of touch, but no systematic research has been carried out.