Studies of the brain’s processing of visual images give a model.
Images are processed from their basic components in a bottom up way by the occipital cortex at the back of the brain. In V1 information is processed according to lines,edges, and corners. V2 and V3 respond to boundaries. V4 responds to colour, V5 to motion.
At the same time the brain uses a top down processing method to try to match the image being formed on the basis of past experience and context. The inferior temporal cortex responds to complex forms such as landscapes, complex colours, faces.
Fodor proposed an influential hypothesis concerning the organization of
human cognition, known as the ‘modularity of mind’. The basic idea, as initially
proposed, is that the mind is constructed from several independently functioning,
insulated subsystems, the inputs of which are restricted to a particular class of
stimulus, and the operations of which cannot be influenced by activity in other
modules or systems.
An exception occurs for the visual system with synaesthesia where a person may here a word spoken and senses a specific colour in response to the word. Synaesthesia is to some degree genetic and it occurs in between 0.05-3% of the population, being more common in children and women. It’s proposed that synaesthesia comes about because of the persistence of a fetal connection linking the word and colour processing parts of the brain.
I am proposing that, similarly, a number of disorders can be thought of as due either to persistence of abnormal inter-system connections or failures in top down processing of stimuli.
For example, Schizophrenia and Asperger’s Syndrome could be largely due to the persistence of abnormal inter-system connections.
Post Traumatic Stress Disorder and Depression can be largely due to the failure of frontal lobe top-down processing to gain ascendency over the bottom-up limbic (fight-flight ) system.