We don’t ‘know’, or even learn, literacy - we do it. The doing is the knowing and the knowing is the doing. It is only ‘behaving’ (reading, say, or writing) which delivers meaning and it is only meaning which is the purpose of behaving. It is only in the behaving, or at the very least the potential behaving, that we can learn or understand. Without some motor involvement, or at least potential involvement, there is no learning.
As we have already seen, we have two brains in our heads: the left and the right. The left copes with language and the right could be said to be ‘mute’, although that may be somewhat overstating the case. Between the two is a thick band of millions of nerve fibres called the corpus callosum. This it is which connects the two hemispheres, which keeps each just about totally informed as to what is going on within the other, moment by moment. Patients with very severe epilepsy were, at one time, treated by surgically cutting the corpus callosum. They are referred to as ‘split-brain patients’. The severance of the corpus callosum almost completely isolates the hemispheres from each other - it certainly does so at least as far as higher level activities like ‘thought’ and ‘consciousness’ are concerned. In fact most nerve pathways to and from body, ears and eyes actually cross over at brainstem level. Information at basic perceptual level, therefore, (well below ‘thought’) crosses over below the corpus callosum and so is not affected by its severance.
Information from (and instructions to) the right side of the body are managed in the left brain and vice versa. Whatever we hear in the right ear is experienced in the left brain and vice versa. The same applies to vision. All fibres from the right side of both retinas cross to the left brain and all fibres from the left side of both retinas cross to the right (and ‘mute’) brain - If we stare fixedly ahead, what is to our left is seen only in the right brain and what is to our right is seen only in our left brain, where language is managed. This information passes below the corpus callosum, and reaches those brain areas which deal with it whether your corpus callosum is intact or not. Images, for example, from both sides of both eyes reach those parts of the brain they should, and can be further processed as usual - but if the corpus callosum is cut this information remains within that hemisphere in which this normally takes place. In other words, normally (if your corpus callosum is intact) all this cerebral information is instantly shared with the opposite hemisphere, but in split-brain patients it is not. This fact can be used to explore language management.
(Springer & Deutsch 1997)