Abstract

My central claim is that philosophers of mind have failed to take adequate account of empirical evidence regarding human consciousness and vision. Experiments on split-brain patients over the past fifty years reveal consciousness in both cerebral hemispheres. I claim specifically that (a) consciousness in the right hemisphere is inherited from our animal ancestors; (b) consciousness in the left hemisphere arose during human evolution in association with language; and (c) the existence of both forms of consciousness provides the best explanation for many aspects of normal human experience. Evidence for two cortical visual pathways in the human brain has been expanding for twenty years. The ventral pathway is specialised for object identification, and the dorsal pathway for the control of actions in respect of those objects. The evidence has been challenged by those who have failed (a) to distinguish between the visual pathways themselves and processes served by the pathways, and (b) to recognise the specific circumstances in which actions draw on one pathway. I claim that in the left hemisphere only the ventral pathway reaches consciousness. The combination of two visual pathways with two centres of consciousness challenges traditional views about perception. I claim that (a) perception is distinct from seeing; (b) perception is limited to the left hemisphere; and (c) the parallel process in the right hemisphere is associated with the emotions. The presence of two centres of consciousness challenges traditional views on the unity of consciousness and on personhood; but it also offers an explanation for conflicting views on the emotions and the existence of self-deception. I distinguish my claims about human consciousness from the Dual Systems (or Two Minds) Theory. Although there are superficial parallels, the latter theory denies that both systems/minds are conscious, and takes no account of the specialisation of the cerebral hemispheres revealed by experiments on split-brain patients. I conclude that philosophy must incorporate empirical evidence if it is to avoid claims of irrelevance