THE SUNDAY TELEGRAPH – 22 November 1998
How the blind really do ‘see’ with their fingers
WHEN a blind person with a guide dog is lost and asks the way, it is not unusual, apparently, for the passer-by to bend down and whisper instructions into the dog’s ear. The reasoning is obvious: guide dogs appear so adept at leading their owners, it is only natural to assume that they must be able to follow human instructions about where to go.
Not so, says Anne Robertson, from Orry-la-Ville in France, who has relied on a guide dog for almost 20 years. She has to know the route she is following in the first place and then instructs her guide dog accordingly with appropriate commands, "left, right, forward, find the crossing" and so on. "The dog’s job is not to find the way but to avoid obstacles and stop at hazards, such as road junctions," she says.
However, her dog has learned the commoner routes she takes and will then literally "guide" her to her destination. "They can learn specific shop names, like ‘butcher’, ‘baker’ and ‘post office’, but seem not to learn the word ‘vet’. My first guide dog always took me to pubs. She liked a glass of beer and thought I should too."
Thus a guide dog’s ability to acquire human-type skills is perhaps not quite as impressive as it might seem, in marked contrast to the phenomenal ability of the blind themselves to compensate for their lack of vision by increasing the acuity of their remaining senses such as hearing and touch.
It is, for example, truly extraordinary that tactile sensation in the tips of the fingers can become so discerning as to be able to translate the raised dots of the Braille alphabet into words.
How is it done? The senses of sight and touch are relayed from the eye and skin respectively along separate pathways and "processed" in anatomically quite distinct parts of the brain, the visual cortex being at the back and the touch, or somatosensory cortex, in the middle of the left side.
One would expect that in the blind, the somatosensory cortex would increase in size and density and the visual cortex would get smaller, but this is not what happens. Rather, it has recently been found that when a blind person "reads" Braille, it is as if he is indeed "seeing", for it is the visual rather than the somatosensory cortex that is activated.
It is impossible to convey the truly remarkable nature of these observations other than to note that they overthrow all the common assumptions of how the brain works. The experiments were performed in people who, having been blind since birth, had never seen the external world, but to compensate for the absence of impulses passing down the optic nerve, their sensory nerves from their fingertips have plugged into the visual cortex. The blind, it would seem, have a means of seeing quite different from and not experienced by the sighted. If the blind can "see" with their fingertips, then perhaps the deaf can "hear" with their eyes and it will be interesting to know if the visual perception of sign language activates the section of the brain involved in hearing.
There is no doubt that the human brain possesses uncanny powers of which we are only dimly aware. Several months ago I described a case of a woman in her 40s, blind from birth, who could detect physical objects in a way similar to a bat’s radar. So, on the way to work, she would "count off" the lampposts until she knew that she had reached her office.
One morning this remarkable extrasensory perception deserted her and she could no longer tell when she had reached her destination. Realising that something must be wrong, she consulted a neurosurgeon. He found and removed a small benign tumour from the frontal lobe of her brain, after which she was able, once again, to count the lampposts.
However, this radar faculty is not exclusive to the blind. Subsequently, Mr R. Pinckheard, from Northamptonshire, wrote to tell me that both he and his daughter also possessed it. "Our Sunday walks often involved my blindfolding her and leading her towards solid objects, such as walls or trees. I never recollect her failing to detect them," he writes.
His "radar" proved particularly useful when finding his way round London during the blackouts of the last war, although it was insufficiently sensitive to protect him from stumbling over the small "cannon" posts on the pavements of the City. He concludes: "My surmise is that I (and my daughter) can pick up the force fields of objects on reaching them."
From which we can only conclude, as Hamlet to Horatio: "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
Copyright: Telegraph Group Ltd