Note FQ — Chapter VIII · MENTAL PROCESSES IN MAN.

And I may add it is not an easy matter to explain to those who have not considered such questions. It is a matter of the correlation of the testimony of the sense-organs. A boy stands before me. I go to him and touch him, and pass my hands downwards from head to foot. Then I stand a little way off and look at him. His image on my retina is inverted. But as I run my eye over him I direct my eye downwards to his feet and upwards to his head. I am not conscious that the stimuli are running upwards along the retinal image. Thus my eye-muscles and my other muscular and tactile sensations seem to tell me that he is one way upwards. The image on my retina tells me, though I am not conscious of the fact, that he is the other way upwards. But he cannot be both! The testimony of one sense has to give way. One standard or the other has to be adopted. Practically that of touch and the muscular sensations is unconsciously selected, and sight-sensations are habitually interpreted in terms of this standard. So long as the two are sufficiently accurately correlated, the practical requirements of the case are met. And it is well known that it is not difficult, with a little practice, to establish a new correlation. This is indeed done every day by the microscopist, for whom the images are all reversed by his instrument. He very soon learns, however, that to move the object, as seen, to the left, he must push it to the right. A new correlation is rapidly and correctly established.