_Learning by thinking_ depends on observation, since in {320} thought we make use of facts previously observed. Seldom, unless in the chimpanzee and other manlike apes, do we see an animal that appears to be thinking. The animal is always doing, or waiting, or sleeping. He seems too impulsive to stop and think. But a man may observe something in the present problem that calls previous observations to mind, and by mentally combining observations made at different times may figure out the solution before beginning motor manipulation. Usually, however, some manipulation of the trial and error sort is needed before the thought-out solution will work perfectly. Sometimes mental rehearsal of a performance assists in learning it, as we see in the beginner at automobile driving, who, while lying in bed after his first day's experience, mentally goes through the motions of starting the engine and then the car, and finds that this "absent treatment" makes the car easier to manage the next day. In summing up the points of superiority of human over animal learning, we may note that-- 1. Man is perhaps a quicker learner, anyway, without regard to his better methods of learning. This, however, is open to doubt, in view of the very rapid learning by animals of such reactions as the avoidance of a place where they have been hurt. 2. Man is a better observer, and this is the great secret of his quick learning. He is especially strong in observing relationships, or "principles" as we often call them. 3. He has more control over his impulses, and so finds time and energy for observing and thinking. 4. He is able to work mentally with things that are not present; he remembers things he has seen, puts together facts observed at different times, thinks over problems that are not actually confronting him at the moment, and maps out plans of action. {321} The Learning of Complex Practical Performances A great deal of light has been thrown on the learning process by psychological studies of the course of improvement in mastering such trades as telegraphy and typewriting. A student of telegraphy was tested once a week to see how rapidly he could send a message, and also how rapidly he could "receive a message off the wire", by listening to the clicking of the sounder. The number of letters sent or received per minute was taken as the measure of his proficiency. This number increased rapidly in the first few weeks, and then more and more slowly, giving a typical learning curve, or "practice curve", as it is also called. [Illustration: Fig. 51.--(From Bryan and Harter.) Practice curve of student W. J. R. in learning telegraphy. The height of the curve indicates the number of letters sent or received per minute. Therefore a rise of the curve here indicates improvement.]