Tuesday, 9 October 2012

Peripheral Vision.


            An aggressor is before you and there is no place to run. He has a knife or broken bottle in his right hand. Where should you be looking to gauge his next move?

            An obvious answer may seem to be to keep your eyes on the weapon, since that is the bit that can harm you. In truth many other parts of his body can attack you and some foes will use the weapon to fixate your attention so they can land an attack with another body part. Watching the eyes “the windows to the soul” may seem logical but some fighters will use these to feint, distract and deceive. In the Bando section of the book the technique of looking at one part of the body and attacking another was described. Some Asian martial arts include mesmerism techniques, tricking the foe into a staring competition to make him vulnerable.

            To attack with his hands a foe must first move his elbows and shoulders. He may first move his feet to change position or balance. He may or may not look at his intended target. To kick he may first move his shoulders to shift balance. Which body part do you watch?

            The answer is, as many as possible. A foe may feint with his eyes but if other parts of his body indicate he is going to do something different his true intentions are more likely to be ascertained. How can you view areas as remote from each other as the hands, eyes, elbows, shoulders and feet all at once? The solution is to make use of your entire visual field.

            The visual field can be divided into your central vision and your peripheral vision. Central vision is your high resolution colour vision and the part of the visual field you use to look at anything you are interested in. It is the part you use for reading, watching television, appreciating paintings and checking out member s of your preferred gender.

What is interesting is that your central visual field is only about 13° of you visual field, with you foveal only about 3°! If you are unfamiliar with how the eye and the visual processing system work this may seem hard to believe, so go ahead and do some background reading on the subject. Vision is a fascinating topic. While the central vision takes up only a small part of your visual field the fovea alone uses something like 50% of the nerve output from the eye.

Peripheral vision is the rest of your visual field. For each eye it is about 60° on the nose side and 100° on the temporal side of the eye. The shape of your face will affect this field at different angles so the visual field of each eye varies from 135-160°. Since most of us have two eyes side by side we have a total visual field of about 200°. Try this out for yourself. Keep looking straight ahead, hold your hands out to the sides of your head and wiggle your thumbs. You can see the movement.

Your peripheral vision lacks the high definition of your central vision. Most of the photoreceptors responsible for the peripheral vision are the Rods, which cannot see colour. If you move a coloured light into someone’s peripheral vision some people will first see it as a white light, and only be able to identify the colour as it moves further into the field. A more practical application is that if you want to see something in dim light, looking past it can often make it clearer. This brings the more light-sensitive Rods to bear rather than the more daylight orientated Cones that predominate in the part of the retina used for central vision.

Another thing that peripheral vision is quite good at is motion detection, which is brings us back to the subject of this blog. Centre your vision on your foe’s upper chest and learn to use both your central and peripheral vision to detect movements of the rest of his body. If a foe attacks you do not look at the attack, then deflect or avoid it. You react as soon as any part of your vision detects it, then change your focus as you counter attack. With a little practice you will be able to make defences and attack just using your peripheral vision. By looking at his chest you can detect telltail shouder movements and are less likely to fall for tricks from his eyes. Also helps keep your chin tucked in against uppercuts. Next time your girlfriend complains you talk to her chest just explain you are practicing self-defence!

Practice using your peripheral vision more in everyday life. Pick things up without looking at them directly. More challengingly, put them down. At the crossing, operate the button without looking directly at it. Word of warning though. Your colour perception is not so good at the periphery so don’t use it to see if the lights or crossing sign have changed!

Here is the late, great Erle Montaigue talking about peripheral vision.