Abstract

This challenging paper presents an ingenious argument for a functionalist theory of mind. Part of the argument: My visual cortex at the back of my brain processes the stimulation to my eyes and then causes other parts of the brain - like the speech centre and the areas involved in thought and movement - to be properly responsive to vision. According to functionalism the whole mental character of vision - the whole of how things look - is fixed purely in the pattern of responses to vision and not in any of the initial processing of vision in the visual cortex. That this functionalist theory of vision is true can be proved with alarming ease. Imagine that just the left side of my visual cortex is replaced by a gadget that has precisely the same input/output relationship to the rest of the brain as the left visual cortex had. According to any view but functionalism, the character of my vision on the right side of my visual field (normally processed by the left visual cortex) would change radically with this change in all the intrinsic properties involved in the visual cortex, with this preservation of nothing but its functional role in bringing about my responses to vision. But, say I, we have enough here to be sure that in such a case there could be no change in the character of my vision. For we know by the stipulation of sameness of output that my responses in speech, thought and movement to the right side of my visual field will be precisely the same as they would have been with the natural left visual cortex and will harmonise just as they would have done with my responses to the other side of my vision. But if half my vision had disappeared or changed I’d be speaking, thinking and acting like someone with problems on the right side of his vision. It is impossible to separate my responses to vision from the character of my vision. The character of my vision is logically determined by the pattern of responses - by nothing but the functional role of my vision.