New Vision > main page > J. Hensil > Vision is a Learned Sense

Vision as a Learned Sense

What would happen if a person who spent their entire life totally blind had their vision resorted? One would assume that they would rejoice in their new sight, living life as those who are congenitally sighted do. In reality, however, these individuals are plunged into a world of sensory overload resulting in severe depression and often suicide. This was discovered after well-meaning surgeons removed congenital cataracts from adults in the early days of modern cataract surgery.

Why does this happen? As infants, we enter the world as poorly seeing entities. Only high contrast, large targets may be distinguished by an infant's visual system. Our visual acuity at birth is about 20/1000. It is only over the first few years of life, while our brains are still highly adaptable and our visual structures mature, that we learn how to see. By age four, our eyes and vision related nervous systems enable us to see 20/20, but this is more complex than a passive act of seeing, it is experience.

Experience tells us what a straight line feels like and correlates it to what it looks like, so that we can distinguish a straight line from a curve by either sensory modality individually. A person who has never had this experience due to congenital blindness can not make the connection, and only through touch can make the identification of a straight line or any other object, as they have never learned what it is to see it.

In addition to shape perception, size is foreign. When something is very close, it appears larger than when it is farther away, a concept alien to one who only knows the object through the size constant sense of touch. Not only are objects unrecognizable by sight, they change size depending on distance and shape depending on what side you are looking at it from. As a car drives farther away from the person with new vision, they can not perceive distance, only that the car is shrinking.

Individuals who have suffered from adult vision restoration can not appreciate optical illusions either, for the same reasons…experience is required to interpret these forms.

The brain is not meant to learn a new sense in adulthood, so the attempt to do so impacts the person negatively. Remember this when reading Stevie Wonder's hopes of getting a retinal implant. How would it actually impact him? Imagine having a 6th sense…what would it be? We can not even fathom what this sixth sense would be, much less how we would adapt to it, just as sight is completely foreign to those who have never experienced it.

Oliver Sachs relates Diderot's words from Letter on the Blind: For the use of those who can see (1749). These words should be heeded by those in the sighted community: ' the blind may, in their own way, construct a complete and sufficient world, have a complete 'blind identity' and no sense of disability or inadequacy, and that the 'problem' of their blindness and the desire to cure this, therefore, is ours, not theirs.'

J. Hensil

For additional reading on this topic, see:

Sachs, Oliver. An Anthropologist on Mars: 'To See and Not See.' NY: Vintage Books. 1995.

Hull, John M. Touching the Rock: An Experience of Blindness. NY: Pantheon Books. 1990.

Valvo, Alberto: Sight Restoration After Long Term Blindness: The Problems and Behavior Patterns of Visual Rehabilitation. NY: American Foundation for the Blind. 1971.

Hebb, D.O., The Organization of Behavior. NY: Wiley. 1949.