There is no kind of mental activity in which memory does not intervene. We are most familiar with it in the case of images, those fugitive elusive copies of sensations with which psychology has been hitherto so much, perhaps too much, concerned. Visual images are the best known of them, but it is important to recognise that every kind of sensation may have its corresponding image. Visceral, kinæsthetic, thermal images can with a little practice be produced, even by people who have never noticed their occurrence. But individual differences as regards imagery are enormous, more in the degree to which images become conscious, however, than in their actual presence or absence on the needful occasion. Those people who, by their own report, are devoid of images, none the less behave in a way which makes it certain that the same processes are at work in them as in producers of the most flamboyant images. CHAPTER XV Attitudes My Sences want their outward motion Which now within Reason doth win, Redoubled by her secret notion.—John Hoskins. The interventions of memory are not confined to sensation and emotion. They are of equal importance in our active behaviour. The acquisition of any muscular accomplishment, dancing or billiards, for example, shows this clearly. What we have already done in the past controls what we shall do in the future. If the perception of an object and the recognition that it is a tree, for example, involve a poise in the sensory system concerned, a certain completeness or ‘closure,’ to use the term employed by Kohler, so an act, as opposed to a random movement, involves a similar poise in a motor system. But sensory and motor systems are not independent; they work together; every perception probably includes a response in the form of incipient action. We constantly overlook the extent to which all the while we are making preliminary adjustments, getting ready to act in one way or another. Reading Captain Slocum’s account of the centipede which bit him on the head when alone in the middle of the Atlantic, the writer has been caused to leap right out of his chair by a leaf which fell upon his face from a tree. Only occasionally does some such accident show how extensive are the motor adjustments made in what appear to be the most unmuscular occupations.