MOTORDOM

Dominion, Volume 30, Issue 266, 6 August 1937, Page 15

MOTORDOM

by

Chassis

THE EYES BEHIND THE DRIVING WHEEL Difference Between “Sight” and “Seeing”

A number of attempts have been made to pin the responsibility for a percentage of traffic accidents on the defective eyesight of motorists. I have heard one authority put the percentage as high as 80, although he has qualified his estimate by saying that psychological causes are partly responsible, says W. E. Hardy, acting-editor The Optician” in "The Motor.”

Sweeping claims like this must be taken with a grain of salt. Nevertheless, as a practical motorist and as one whose job it is to know a good deal about sight, I never hestitate to recommend budding drivers to have a care for their sight.

The "can you see a number plate at 25 yards” test is no more than a compromise. In technical language, it merely tests whether you have about 50 per cent, of normal vision. Millions of people are better off wearing spectacles, although their naked vision would enable them to pass the number plate test.

Up to the point, it is true that the better you see the safer you are likely to be when driving. But the quantitative aspect of sight is not the most important factor when considering the relationship between vision and driving efficiency—and enjoyment, too, let it be added.

How many people realise that there is a subtle difference between the functions of "seeing” and “sight”? It is quite possible for a person with perfect eyesight to be effectively blind. His attention is concentrated on some one part of his field of vision and he is blind to objects in other parts of this field.

A recent investigation has shown that “accident prone” drivers usually make fewer head movements than better drivers. They have a bad habit of concentrating their gaze too much on some extraneous object and to lose sight of other more important objects. Their “sight” may be good, but they are bad at "seeing.” For such people there is an exercise designed to correct the bad habit. They should constantly and regularly practise moving their gaze over the whole of the field of vision, moving the head with the gaze. This latter point is important, because, although the peripheral pgrts of cur eyes are very sensitive to movements of objects, they are comparatively poor at discerning definition and detail. For precise “seeing” objects must be focussed on the central part of the field of vision. An ability to range over‘the field of vision is extremely valuable to motorists, not only from a safety standpoint, but as a contribution to the enjoyment of motoring. The more we see the better we enjoy driving. ■ Another important factor in driving is the ability to recognise .objects and to judge their distance and speed. Again, this ability is not entirely dependent on the possession of 100 per cent, sight, although this is a distinct advantage. The ability rather depends on recognising and interpreting changes t:

in the shape and size of an on-coming vehicle, the meaning of shadows, and on differences between the images formed on the back of each eye. It is as much dependent on intelligence as on vision.

However, to some extent, the pure judgment of distances depends on the amount of muscular power the eyes have to exert in order to converge so that each eye is aligned on the object under view. Here the one-eyed driver is at a disadvantage. Generally speaking, he is apt to be less accurate as a judge of distance than the driver who uses both eyes for seeing. Nevertheless, a one-eyed driver can, to quite a large extent, cultivate an ability to judge distances, which shows that the ability is acquirable through intelligent application and by constant practice. ....

Unfortunately, it is a fact that many of the people who are bad judges of distance are unaware of their fault. Some with whom I have driven have even boasted of their ability. Their attempts to justify this boast have given me many anxious moments. Every experienced driver knows glare. But not every driver knows all the insidious effects of glare. _ One of the experimental methods of inducing sleep in laboratory experiments is to turn on a fairly bright light a little above and in front of a person’s eyes and tell him to look at the light continuously. If he is left alone and follows direction, or if he is made to perform a more or less monotonous repetition task, drowsiness soon sets in. Here is a tip for insomnia sufferers! Glare, then, induces drowsiness. Performing a repetition task accelerates the drowsiness. Glare also blunts the vision; makes the eyes less sensitive. The speed with which a driver can respond to emergencies is very definitely reduced. Thus, it is wise to be on guard against conditions which subject your eyes to glare. A careful study of the relationship between sight and motor driving efficiency seems to point to this conclusion: how we use our eyes is every bit as important as the amount of sight we enjoy. There are thousands of perfectsighted motorists whose "seeing” abfiitv is very defective. They are missing a‘lot of the pleasures of motoring and they may be well on the way to qualifying for inclusion in that small group of what the insurance companies call "accident'prone” drivers. Most of these drivers can avert this fate if they will only: (1) Take the usual precautions to ensure their sight being as good as either Nature or optical science can make it; and (2) precise “seeing” for the next few months.