Monday, November 11, 2019

The limitations of blindsight

Blindsight, made famous by a book of the same name in science fiction circles by Peter Watts, is a disorder caused by damage to the primary visual cortex.  Sufferers typically lose all ability to consciously perceive any sight from the eye corresponding to part of the cortex damaged.  Which sounds sort of like blindness.  If you cover their normally working eye, but a tomato on a table in front of them, and ask them what's there they'll have no idea and be unable to do so.  But this is called blindsight rather than just blindness.  If you then ask this person to point to the object in front of them they'll point right at the tomato.

How does this work?  Well, the brain is composed of different parts that connect to each other in different ways and serve different purposes.  Strange as it may seem the part that corresponds to you knowing that you know there's a tomato there and the part that lets you point to the tomato are different and its possible to cut one off from your eyes while leaving the other attached.  The brain has a certain amount of plasticity but also a certain amount that's fixed and it seems that brains can't adapt to this sort of damage.

If you can still pick up things when you aren't aware of them then you might ask why evolution ever bothered to give us consciousness in the first place.  If we don't need it to interact with the world around us, then what is it doing?  Couldn't we conceivably be better off without wasting precious brain space on being aware of the world when a leaner and more efficient brain might speed through life without wasting time on reflection?  This is the question that Peter Watts was asking in his book *Blindsight* but as you might guess from my recent post on AlphaStar versus AlphaGo the answer is probably a no.

Indirect consciousness of consciousness

Consciousness is one of those words that people argue about endlessly, see the entry in the Stanford Encyclopedia of Philosophy.  Beyond philosophy there's been a certain amount of scientific study of consciousness too.  One of the most interesting, ironically enough, has its roots in Behaviorism.  Behaviorism is the idea in psychology that we can't necessarily trust what people say or believe about their motivations so we should root our conception of psychology just in how people behave.  Or in other words that we should avoid anthropomorphizing people.  It worked as a paradigm well enough and eventually some people in that tradition asked, "Well, if we can't just use introspection how can we study consciousness?"

Well, one obvious behavior tied to our commonsense idea of consciousness is that people can talk about their experiences.  If you show a tomato to a conscious person and ask them what they saw they'll be able to say that they saw a tomato.  If you show a tomato to an unconscious person then they won't.  Even after they woke up.  Even if you were able to open their eye without waking them up.  So that's a lever scientists were able to use to study consciousness scientifically through experiment.

One important idea that came out of this was the idea of subliminal sensations.  If you project a tomato on a screen for a certain number of milliseconds they'll be able to tell you there was a tomato there.  And at a small enough duration there'll be no effect on the subject.  But there's an in between region where they won't know what they saw but the image can still have an effect on their behavior, say in how fast they press a button if a piece of text they see next is a vegetable or not.  They'll be faster on the button if they've been primed with a tomato.  This is what is known as subliminal priming.

So we're back to information getting into the brain but us not being aware of it.  These scientists aren't looking directly at consciousness, the mystical sense of selfness, but they are looking pretty directly at our conscious awareness or unawareness of things.  You can even hook some sensors to people's brains and be able to tell if a stimulus was subliminal or not.

The importance of being liminal

Ok, so now that we can look at conscious awareness in the eye, so to speak, what does it do.  Well, the first is sort of implicit in the nature of how the testing is done.  People can speak of what they know but of the rest they must remain silent.  As social creatures being able to talk to each other about our surroundings is very important for planning and coordinating.  And that's great as far as humans or other advanced creatures go but is this some facility of the brain that had to evolve along with language?  If so why do so many different creatures have varying different abilities to communicate instead of getting it all at once.  Well, there's another important thing that comes along with conscious awareness.

Subliminal stimuli disappear from the brain in a second or two.  They fade quickly away in the sensors we strap to people's heads.  The effects fade rapidly away in their responses to tests too.  It seems that everything that goes into your memory gets there by going through conscious experience.

And that's the reason you can't have a creature without consciousness and expect it to interact productively with the world.  I can sit down at a table, close my eyes, wait a second, and still point to the objects I'd seen on the table through memory.  Someone relying on blindsight can't do that.  Maybe, for the philosophers that believe in a metaphysical consciousness that exists beyond matter the person with blindsight had qualia in some place beyond our mortal ken but it didn't have any effect on the world we live in.  But it didn't happen in this world and that's why evolution keeps this sort of conscious experience around despite the fact that it involves precious brain matter that could have been used for something else.

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