This brings us to the subject of "concentration." A person who is sitting with closed eyes is not necessarily concentrating - he may be just resting; he may be asleep. If he is dreaming, that is not concentration either. Concentration is an act of the will during which the mind actually sees, during which the seeing faculty of the mind acts, and also the hearing faculty of the mind acts. Whereas our physical being uses five senses to perceive things, our mental being uses only two - seeing and hearing. When we visualize, we see things by the help of the mind.