Can a child, blind for several years since birth, benefit from optical correction of the eye? Is the brain “plastic” enough to make use of the information from the eyes later on in life?
These are the questions that had interested Professor Pawan Sinha of the Cognitive Sciences department of MIT in Cambridge, MA, U.S. Starting with these, he had gone ahead and discovered a variety of surprising (and happy) results on how the human brain adapts to experiences and challenges.
Why human?
I have specified the term ‘human' above for a reason. All experiments to answer the above questions had so far been done on animals, with depressing results.
They had suggested that there exists a critical (presumably short) period for visual learning after sight is restored.
But these are a boon for animals, invariably on dark-reared cats. Sinha set to research on humans.
To this end, he has combined service with science. Through a scheme that he funds, called Project Prakash, he has helped many Indian children in Delhi, Rajasthan and UP, who were born cataract blind, regain sight through cataract surgery.
He then studies them in an effort to answer the above question.
Several novel things
His studies on these people have revealed several novel things hereto unknown. The first is that there may not be a critical time period at all.
Be it 10 years or even 22 years after birth, when sight is given, the individual is able to learn a variety of functions using vision.
Some of these are shape matching, colour matching, face recognition and so forth. Where and how do these functions occur in the brain? Sinha answers these by doing functional magnetic resonance imaging or FMRI on these individuals.
FMRI is an admirable, clever tool that monitors the flow and use of blood as it passes through cells and tissues, giving them oxygen for metabolism.
The iron in the haemoglobin in blood is magnetic and its property changes as it takes up and releases oxygen. You thus place the individual in the FMRI machine that looks like a bed with a tunnel-like cover (containing the magnetic field) in which you place his head.
You now ask the person to do a task, and monitor which part of his brain (one of the hemispheres, occipital lobe, cortex, etc) is active and “lights up” as he performs the function.
Using FMRI on several volunteers who benefited from Project Prakash, Sinha finds a novel result.
That not only do these subjects look and learn, but their responses are registered (hard -wired, if you will) in specific regions of the brain. The brain is indeed plastic, making new and location-specific neural connections within its parts, and this happens regardless of when sight was restored after birth.
How does such a person (or for that matter, we as growing infants) match the various sensations?
The question
In this connection, note the question which the scientist William Molyneux posed three centuries ago to the British philosopher John Locke.
He asked “Suppose a man born blind and targets by his touch to distinguish between a cube and a globe. Suppose the blind man be made to see; query, whether by his sight , before he touched them he could now distinguish and tell which is the globe, and which the cube?”
When Sinha posed this question to the audience, a majority of them said he would.
Wrong! He cannot, at first sight. The tactile sense is not necessarily transferred into the visual sense. A correlation between the two needs to be learnt which, of course, is easily done.
Integrating patterns
Sinha's work has further shown that as vision is acquired in the early stages, there appear to be some difficulties in integrating patterns.
Motion or movement of the object appears necessary for such integration. A subject shown two squares on the computer screen calls them (rightly) two.
When they partly overlap, he calls them three (two original ones, plus the overlap region counted as the third). But when the two squares are shown moving, and overlapping, the subject recognizes them as two moving objects.
Motion cues
Motion cues thus provide critical information for object integration and segregation. It is this dynamic information processing that allows us to integrate various cues such as face perception, perceiving causality, touch to vision mapping and so on. With time and learning, these become normal or second nature.
We thus see in these newly sighted people an image of what all we ourselves went through to integrate the various cues, and incorporate them in our brains, as we developed visual perception and acuity in all its dimensions, as we grew from birth to childhood. It is never too late to learn and master.
Lastly, what was Locke's answer to Molyneux? “For though he has obtain'd the experience of, how, a globe, how a cube, affects his touch; yet he has not attained the experience, that what affects his touch so or so, must affect his sight so or so.; Or that a protuberant angle in the cube, that pressed his hand unequally, shall appear to his eye as it does in the cube”.
This was the style of English prose of 1694. Simply said, he meant “no”.
dbala@lvpei.org
