When sitting in the rear of a hall listening to an address, by giving my whole, conscious attention to what is being said, I am able to hear everything said; but at the end of the lecture I always find myself in a state of genuine fatigue. It is not a state of fatigue incident to the difficulty of comprehending. It is a fatigue wholly different from that which results when I sit in the front part of the room where I can hear easily. It is a fatigue which is due entirely to the giving of attention — a fatigue of strain, not a fatigue of the ear...FROM THE BOOK