If Seeing Is Believing, How Do We Know What We See?

The eye is a simple optical instrument. With internal images projected from objects in the outside world, it is Plato’s cave with a lens. The brain is the engine of understanding. There is nothing closer to our intimate experiences, yet the brain is less understood and more mysterious than a distant star.

We have only to open our eyes, and spread before us lies a banquet of colors and shapes, shadows, and textures: a pageant of rewarding and threatening objects, miraculously captured by sight. All this, from two tiny distorted upside-down patterns of light in the eyes. Seeing is so familiar, apparently so easy, it takes a leap of imagination to appreciate that the eyes set extremely difficult problems for the brain to solve for seeing to be possible.

Light does not enter or leave the brain, locked privily in its box of bone. All the brain receives are minute electrochemical pulses of various frequencies, as signals from the senses. The signals must be read by rules and knowledge to make sense. Yet what we see, and what we know, can be very different. As science advances, differences between perceived appearances and accepted realities become even greater.

What is striking is the huge amount of brain contributing to vision, giving immense added value to the images of the eyes. Where does this added value come from? Even in ideal conditions object perception is far richer than any possible images in the eyes. The added value must come from dynamic brain processes, employing knowledge stored from the past, to see the present, and predict the immediate future. Prediction has immense survival value. It makes fast games possible in spite of the physiological delays from eye to brain, and brain to hand. Moreover, anticipating dangers and potential rewards is essential for survival — made possible by buying time from seeing objects distant in space.