Psychology experiments give us a good reason to think that there are multiple streams of thought going on in our minds. For example the classic experiment where the brain stem is cut, separating the right and left hemisphere, demonstrates that the two sides of the brain can continue to function and perform plenty of tasks without contact between the two. The left side of the brain is clearly conscious in these cases and can carry out a conversation on its own. The right hemisphere is a less familiar beast as it lacks the ability to speak but it can process images and do spatial tasks similar to before. If you are willing to admit those who can’t speak as conscious, then you could reasonably say that each hemisphere was a largely separate consciousness after such a cut. Of course, in normal brains, these two streams are intimately linked, sharing lots of information about language and images back and forth, making any boundary invisible.
This lovely video demonstrates the above:
Might a normally functioning brain have a similar split to this one – one which we don’t even notice? We commonly talk about our ‘subconscious,’ and infer its existence from conclusions that come to us on topic we have never contemplated consciously. Is it possible that this ‘subconscious’ is another stream of consciousness having a similar experience of life to us, the ‘conscious’ part? I don’t see why not. Indulge me in some speculation.
Our subconscious probably exists in order to make it easier for our conscious mind to deceive others. As an example, if you are befriending someone powerful you otherwise don’t like because you are planning to take advantage of their power, that is something you might not want to give away to them. However, if your conscious mind had to decide whether to befriend them in the first place by calculating how useful they would be in the future, it would be very aware of the ploy it was trying to pull and that knowledge would leak through in what you said and how you behaved. In the arms race between deceivers and those trying to catch them out, there would have to come a point where the best and perhaps only remaining strategy for deceivers was to believe their own lies. If your conscious mind really believes that it likes this person and has no intention to exploit them, and it is the part controlling your signalling behaviour, then there’s no way to catch the deceiver at their game! Evolution would then could build a mind that is split into two decision makers, with our conscious part thinking mostly nice things, and the subconscious sitting to the side doing its ‘dirty thinking’ and passing on instructions. “Be helpful to this (hot) woman.” “Of course you love Jazz (just like these high status people do).” “Be helpful, (because people are watching).” All the while the self-serving motivations for our actions are hidden from us so that we are at no risk of giving away our true intentions. If ever our behaviour seems peculiar to our conscious mind, there’s no problem, because as shown in that video above we are brilliant rationalisers who are always able to explain away our own self-serving behaviour.
How sophisticated would this subconscious have to be to serve its role? At a first glance, it would have to be pretty smart! We need this subconscious to process almost the same information that comes in to us, scour it for useful bits, and then processing it into simple impulses it can send to its conscious counterpart. Unless most of this processing is being done by the conscious with occasional memos sent down to the subconscious for its consideration, then the subconscious would need the broad range of skills that our conscious minds need - language, spacial and visual skills, planning, social awareness, etc. In this possible design at least the subconscious is an incredibly Machiavellian mirror of ourselves, doing the thinking we pure beings can’t do.
There are problems with this approach though: our subconscious might be a dumb rule follower (people = act nice) rather than a smart mind that processes each individual situation on its merits; or it could be outsourcing most of its ‘thinking’ to other parts of the brain and just piecing together simple little bits of information it receives without having an ‘enunciated’ stream of thoughts. How might we detect the level of sophistication of our subconscious? To test whether it is an unsophisticated rule follower you would hand it ever more compliated calculations to make and see how good it is at determining what is in its carriers self interest. If it is easily tricked into sending us bad advice when there are conflicting issues it has to weigh up, that would be an indication we have a rule follower. If, on the other hand, it is able to adapt to new and unusual circumstances easily and always produce a sensible result, that is evidence for a smarter mind.
As for how aware of itself the subconscious would be, and how much information processing it would need to do, I have no idea, nor do I know how this could be tested. So over to you to help me think of some experiments!
UPDATE: Robin Hanson proposes that the image and action parts of the brain are more integrated and different triggers activate different patterns of thought.