Page:Popular Science Monthly Volume 50.djvu/71

Rh motor elements. Dr. Browne says further that "the muscles not only by the locomotion which they make possible enormously widen the field from which our sense impressions are gathered, but also, by the experience which their own activities involve, expand our mental resources a thousandfold."

How does this come about? it will be asked. Let one reach out his hand in any fashion, and he knows exactly what movement he has made. Does he know because he saw what he did? Then let him close his eyes and move his hand in any other fashion, and he knows just as well what the movement was as if the act were performed with eyes open. Did he know it because he had willed to move the hand thus? Not so. It must be granted that he willed to do it, and pictured in his mind previously the movement to be made; but that was the end of it in one particular. From that point it disappeared from his consciousness. The picturing of the movement with the intention to make it was the last thing he was conscious of so far as the movement is concerned. Because of that willing a discharge was set off from the motor centers, and the next thing in his consciousness was a perception coming from the sensations which arose from the movement. He then compared that perception with the previous image of the willed movement. They agreed, and he knew just the movement he had made.

But it will now be asked, How do sensations arise from the movement? Such a question is most pertinent at this point. Sensations arise from movement because there are distributed through the muscles, the joints, ligaments, and tendons, even the skin itself, sensory nerve ends which are affected by the movement and convey to the brain sensations of that movement. Out of these sensations the mind perceives what has been done. There is, then, connected with the motor or muscular side an important sensory side. We may go further than to say it is connected with the motor side; it is really imbedded in it. This important sensory side, it will therefore be seen, can not perform its function and carry information to the brain unless the motor side is used; and the more various the employment of the motor side, the larger the knowledge stored up in the brain from its sensory counterpart. The motor and the related sensory are developed by and with each other. The ideas resulting therefrom are sensory-motor ideas; and we have at last come to have some scientific appreciation of the far-reaching importance of these sensory-motor ideas as a part of the structure of the mind and as a means of producing fuller as well as higher mental development.

Ideas of time and place and position in their basic and most important elements are motor. Ideas of form involve more of motor impressions than of optical impressions. By the use of