This is from another list but I thought it relevant here. I’ve also posted it to CSGNet.
As a young research student, Hermann Helmholtz was told by his professor that it would be impossible to measure the speed of nerve conduction. It would be too fast. But, like all good students, he ignored this advice. In 1852 he was able to measure the speed of nerve conduction and showed that it was rather slow. In sensory neurons it takes about 20 msec for the nerve impulse to travel 1 meter. Helmholtz also measured “perception time” by asking people to press a button as soon as they felt a touch on various parts of the body. These reactions times turned out to be even longer, being more than 100 msec. These observations show that our perception of objects in the outside world is not immediate. Helmholtz realized that various processes must be occurring in the brain before a representation of an object in the outside world appears in the mind. He proposed that perception of the world was not direct, but depended on “unconscious inferences.” In other words before we can perceive an object the brain has to infer what the object might be on the basis of the information reaching the senses.