ABSTRACT

The British physiologist Sir Charles Sherrington was the first to suggest that, contrariwise, developing sense organs led to the need to grow brains to make the best use of them. Interpreting sensory information to predict the immediate future gave even these very simple creatures the foundations of physics and philosophy: the ability to perceive time (soon, less soon); the relation of time to distance and movement (fast or not so fast); and probability (opportune, risky or futile to dodge or pounce). Visual illusions illustrate that there are many different levels at which the changes that age brings to our nervous systems affect our interpretations of the world. The grid of light-sensitive cells at the back of the eye is called the retina (Latin for a “net”) that acts like the array of pixels in a digital camera, each of which registers whether, and how much, light falls on it.