I came across an old but rather fascinating article about a gentleman who had suffered two strokes which destroyed his visual cortex, rendering him blind. The brain processes the raw input from the eyes into what we might term 'sight' in quite specific areas, and, absent these, we are unable to see.
The patient's eyes were of course still functioning, as were the optic nerve, but the inputs were no longer being converted into the subjective experience of seeing. However, despite not having 'sight' per se, the patient was still able to react to visual stimuli: he could correctly read and respond to facial expressions, and even managed to navigate an obstacle course unaided.
How is this possible without the subjective experience of sight? Well, simply put, there are other areas of the brain--those that control emotional reactions and obstacle avoidance--which also use the visual input, but were not damaged in the stroke.
The article was linked in the context of a discussion of consciousness--is it a metaphysical phenomenon, ie, the result of some 'ghost in the machine', as the saying goes, or simply an emergent phenomenon of the interlocked operations of the disparate parts of our brain?
Human beings are nothing if not subjective, and our subjective experience is certainly NOT of being the result of the cooperative function of the various hardwired sections of our brain. Our subjective experience is one of a singular conscious entity experiencing the world, reflecting on the world, and making decisions about how best to act in it. We do indeed experience the world and decide how to act, yet even those processes are hardwired, and our ability to engage in those actions and perceptions is directly tied to certain specific sections of the physical brain. In the case of the patient mentioned in the article, when his visual cortex was damaged, then he could no longer see despite that his eyes were in perfectly good working order. Yet, he could still process input from his eyes in other ways, because the areas of the brain that do so were still intact.
This is hardly the only example: I have a friend, for example, who suffered brain damage in a car accident, changing her mental capacities in ways that her conscious mind struggled to accept. My grandfather went through a long and pitiable period of some years in which the physical state of his body and brain decayed rapidly, changing his personality markedly in the process (he would, for example, swear reflexively and often propositioned the female residents of the nursing home, actions which he would never have dreamed of engaging in had his brain not been ravaged by age). Alzheimer's wipes out memories; trauma to the organism can result in change of personality; children not taught language at the early ages when the brain is still rapidly developing can seldom be taught later once that growth has slowed.
If there is a ghost, then its abilities, perceptions, and actions are indistinguishable from those of the machine. What does it know that the brain does not? What does it perceive that the brain does not? What does it do that the brain does not? Where does it process information, if not in the space inside our heads? What are the properties which distinguish it from the physical brain?
That the 'self' is an emergent property of chemical reactions within a chunk of gray matter seems counter-intuitive and demeaning--something within us balks at the conclusion. We yearn for a metaphysical validation of our subjective experience, for the essence of the 'I' to transcend ephemeral matter and touch (or descend from) the eternal.
Whether that desire has any basis in a reality beyond our own is a question that perplexes me. Matter returns to divinity, as the song says; whether there is a divinity remains to be seen, but that we are matter seems difficult to question.