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@janesix
You must consider the possibility that the conscious mind doesn't "do" anything in the sense that it is just a trivial side-effect of the normal operation of our brain. You might as well be asking, "well, what does car exhaust do?" In terms of the functioning of the car, it doesn't do anything. It's not part of the car's necessary operation, it's just a byproduct.
That said, while consciousness can't change choices already made, it can influence future actions. Behavior is cyclical. We receive information about our environment. Our brain processes that information and decides upon a response. Our response then effects and changes the environment. We receive information about the environment, etc.
Through our ability to change the environment, we can then change our own future behavior since our behavior is dependent upon the environment. Our consciousness is in this process, so necessarily it can effect that process. But the effects of consciousness come after the decisions of the subconscious. The conscious mind isn't doing the deciding, it's doing the rationalizing. It assigns meaning and constructs a pleasant little narrative, after the fact.
Consider Alien hand syndrome. With this condition your hand is operating as if it has a mind of its own. Its behavior is not random or erratic. It is capable of performing deliberate and complex acts that the conscious mind is completely unaware of. So clearly the conscious mind is not a necessary component of decision making or action taking.
Consider other examples of severing the two halves of the brain:
When subjected to a series of lies sent only to one side of their vision or the other, people with split brain would only report on lights flashed on the right side of their field of vision. But when asked to point to any light that flashed, they would correctly point to every light that flashed even the lights they did not report as having seen flashed! So clearly the conscious mind is not necessary in processing input, making decisions, or taking action!
Most striking, I think, is this:
Certain experiments that Gazzaniga conducted with split-brain patients also led him to develop the concept of the “left-hemisphere interpreter”. In one of these classic experiments, the split-brain patient had to point with his two hands at pictures of two objects corresponding to two images that he had seen on the divided screen (one with each of his two separated hemispheres). In the test shown here, the patient’s left hand is pointing at the card with a picture of a snow shovel, because the right hemisphere, which controls this hand, has seen the projected image of a winter scene. Meanwhile, his right hand is pointing at the card with a picture of a chicken, because his left hemisphere has seen the image of a chicken’s foot.But when the patient is asked to explain why his left hand is pointing at the shovel, his talking hemisphere—the left one—has no access to the information seen by the right, and so instead interprets his behaviour by responding that the reason is that you use a shovel to clean out the chicken house! Experiments like this show just how ready the brain is to provide language-based explanations for behaviour.
So not only is your conscious mind not required in input, decision making, or action taking, but it'll readily invent completely fabricated justifications for why you took a certain action!
