A person who has dementia loses the uncanny ability normal individuals have for judging the passage of time. He may repeatedly ask you what time it is, feel that you have left him for hours when you are out of sight for only a few minutes, or want to leave a place as soon as he has arrived. It is not hard to understand this behavior when you consider that, to know how much time has passed, one must be able to remember what one has done in the immediate past. The person who forgets quickly has no way to measure the passage of time.
