First, I want to touch briefly on clinical facts which, in my opinion, totally validate the principle of localized memory images: These are clinical instances of sensory and motor aphasia, and cases of the so-called tactile anaesthesia of the hand. The former are probably well known by now, so I need not go into detail; but the importance of the latter is debated. Two related sets of facts provide support. On the one hand, cases have been seen where circumscribed cortical damage in the middle third of the two central gyri leads to permanent deficit, where the hand fails to recognize objects by touch, although disturbance of sensation itself can barely be detected. On the other hand, there are cases of spinal or peripheral disease where sensitivity, and—I stress—also muscle and position sense, is most severely disrupted, with only minor disturbance of tactile perception. The last-named cases demonstrate to some extent that even a very weak and patchy projection system can still conduct messages to the brain sufficient to support primary identification, provided the central projection fields and therefore the remembered images—tactile images, as we can call them here—are preserved. However, cases of the first [Ed] type can be based only on loss of primary identification itself, since disturbance of projection pathways themselves is clearly minimal. The principle that remembered images are localized to corresponding projection fields is established beyond all doubt by such facts, and thus this principle can be fairly applied to all projection fields.

After this, it appears obvious that possession of such remembered images—contents of consciousness [W], we might say—depends directly on the projection system and sense organs by which those images were obtained. The consciousness of a person with poor eyesight, or one with generally deficient senses, is thus quite different from that of a normal person. An individual born blind will certainly have no remembered images of visual sensation. Were his sight to be surgically healed, this would provide a situation we otherwise see only when the pathology of visual agnosia occurs. Just as for an individual born blind, so too for one born deaf, the content of consciousness totally lacks an entire category of memory images originating from the sense of hearing. In partial cortical deficiencies, as observed from time to time in those who are mentally defective from birth and also have sensory deficits such as deafness, there is a similar lack of remembered images due to abnormal development of central projection fields. No less instructive in this connection is a comparison with animal brains. Humans have only a vestigial olfactory bulb, whereas many mammalian species have an olfactory bulb occupying a significant part of their cerebral hemispheres, with a separate ventricle and separate surface gyri. Everyday observation shows just how different is the consciousness of such animals, for example that of a dog from our own. It appears to be full of remembered olfactory images, and the animal, snuffling here and there, revels in all its joyful frame of mind, like the gourmet at table, or the eye of an artist beholding beautiful forms. The content of consciousness shown in this way depends on the state of the projection system and central projection fields, a relationship suggesting the following principle: Consciousness is a function of the central projection fields. If the assumption—that projection fields occupy the entire cortical mantle—is confirmed, then the corollary follows: Consciousness is a function of the cortical mantle.