Vision and Racing

By Ron Watson

      Racing requires increased driver vigilance and search habits such as localization or identification of objects in cluttered visual scenes. We must react to visual input such as positions of other cars on the track, flag signals displayed by marshals, the glistening of oil or water on the track, dirt, sand, rubber marbles or stray car parts on the track surface which may require, depending on their location, the driver to change position on the track or alter his line in the corner.
      These decisions will often demand half second response times. It is obvious that acute vision is paramount to insure quick reaction times. Driving decisions are based on what you see. What you see can be classified as interaction of the six basic visual attributes which are:  visual acuity, depth perception, eye coordination, field of vision, night vision and colour vision.

Visual Acuity:  refers to the ability to recognize detail. We are all familiar with the designation 20/20 (or 6/6 for those who are metrically inclined). 20/20 vision means you can see a 5 inch letter from a distance of 280 feet. 20/40 means you can see that same letter at 140 feet. Thus if you have 20/40 vision you must be twice as close to see this letter. Many people have 20/15 acuity which is better than 20/20. These individuals can see this 5 inch letter at 372 feet.

      A number of factors affect visual acuity. The first thing that concerns us as racing drivers is that visual acuity decreases as the speed we travel increases. The visual acuity previously mentioned is referred to as static acuity--i.e.the acuity measured when you are standing still. When you are in a moving vehicle we then refer to dynamic acuity. Dynamic visual acuity decreases the faster you drive. For example, a sign you can read at 400 feet standing still will not be seen until 260 feet when traveling at 70 miles per hour. This change results from the change in size of the retinal image and its movement across the retina.

      Visual acuity is decreased by refractive errors such as myopia (nearsightedness), hyperopia (farsightedness) or astigmatism. These can usually be corrected by wearing glasses, contact lenses, or by refractive surgery such as lasik. Our vision also changes with age. As we mature our focusing ability decreases and it becomes more difficult to change focus from distance to near objects. Pupil size decreases and we require more light to see well. Changes occur in the clarity of the lens of the eye causing light to scatter, making it more difficult to see at night. This is more a concern driving home from the track since we as vintage racers do not as a rule race in the dark.

Depth Perception:  In basic terms this refers to distance judgment. Whether passing, stopping or avoiding a spinning car you rely on your ability to accurately judge the distance between objects or the distance between you and an object. To judge distances accurately a driver should have as close as possible to balanced vision in both eyes(ideally 20/20 or better in each eye). Depth perception is also dependent on good eye coordination.

Eye coordination or binocularity:  refers to the way the twelve muscles that move the eyes are coordinated. The eyes must be properly aligned so that you can see clearly and without eyestrain. A problem with binocular vision such as over or under convergence can result in fatigue, blurring or doubling of vision.

Field of Vision:  refers to the ability to perceive objects to the side, above and below without moving your eyes or turning your head. A wide field of vision enables you to be aware of the big picture and our position in it. The normal horizontal field of vision is about 180 degrees. As with visual acuity, this field of vision is reduced by speed. At 70 mph you are able to use only 25% of your normal side vision due to the blurring of stationary objects close to the side of the car. We are further restricted by the fact we wear helmets which limits our peripheral vision. Thus, it is very important to keep our eyes constantly moving and scanning, and to use our mirrors. These mirrors must be adjusted so as to provide for the maximum lateral vision. It is critical that this mirror adjustment be checked each time before going onto the track, since vibrations of the car, and people walking by in the pits and bumping the mirrors can cause misalignment.

Night Vision:  As mentioned earlier this is not a primary concern for those of us that race only during daylight conditions. However it is important to realize that being outdoors all day in the bright light without sunglasses will require a longer time to dark adapt once the sun has set. We will adapt to night conditions quicker if we have been wearing sunglasses during the bright hours. This prevents the bleaching out of the photopigments in the retina which are necessary for night vision. It is important to be sure sunglasses are not worn once the sun sets.

Colour Vision:  or for our American friends, color vision. The recognition of colours is a complex visual task. About 8% of men and 0.4% of women suffer from defective colour vision and hence perceive colours differently from the majority. Of real concern are those classified as protanopes (1.2% of the male population),whose visual perception is insensitive to very deep red colour. These individuals tend to confuse reds, yellow and greens. These drivers derive some benefit from our highway and city traffic signals due to their brightness and colour saturation as well as by convention that the red is placed at the top of the red yellow and green signals (other than in Quebec, where many traffic signals are orientated in a horizontal position). Colour defectives require about twice as much time as a normal driver to act upon coloured signals,and the incidence of errors in the recognition of the colour is much higher.

      On the track the flag colours do not differ in brightness, and they are more difficult to see due to the fact that they may be waved, and the background is usually that of a bright day, which lowers the contrast between the flag and the background. Colour defective race drivers must be extremely vigilant when interpreting race course flags.

      As you can see, we as vintage racers must realize that with age and increased speed our visual acuity decreases, our field of vision decreases, our depth perception decreases, our colour discrimination decreases, and our reaction times decrease.

      My advice would be for all MG drivers to SLOW DOWN on the track so that Watson in his '61 Midget #63 has a chance to keep up. I hate wondering where everyone went.

Dr. Ron Watson is an Optometrist practicing in Burlington Ontario and is past co-chairman of the Motorist Vision Committee of the Ontario Association of Optometrists.