How
much of this page do you think you can see at one glance? A lot! Let me change the question a bit, how much
of it can you see clearly? If your answer doesn't change even now, you better take this test. Look at the first letter of
this paragraph, seeing exactly that try reading this line. Even though this entire paragraph may come under
your visual field, it does not allow you to read beyond a certain area. This region in the eye is called the macula, where
the density of cones is maximum. The obvious question would be why is such a thing ever required? Why isn't the entire
retina composed of even density of cells? Would we be able to see much better if the entire retina were a macula? Even
though we capture the entire scene, we recognise only a part of it. You might have observed an illusion with a dark spot
and haze around. By concentrating at the center for a few seconds the haze appears to vanish. This is not a defect
with your eye, it is it's property. If the region surrounding the macula does not detect any change in the color it is receiving,
it neglects it, I mean takes it's concentration away from there. In order to over come this, your eye keeps on changing
its centre of view by a very small amount so that you experience a change all the time. This is the reason many of them find
it difficult to realize such illusions.
The cells interrupt the brain only when they find a difference. When you are watching TV or busy reading some interesting
book suddenly if a cockroach passes by, you turn towards it, but before that you din't know what was going on there.
The name "Motion detection" is a misnomer. It does not try to detect motion, but indirectly does it by having this interrupt
capability.
So if our entire eye were to be made of macula our vision wouldn't improve any further, since we don't need to process so
much information. All our recognition and observation is taking place in the macula region. The surrounding region is only
required if there is some movement to be observed and hence the name.
