Look at an object within arm’s reach, a pencil for instance. Now close your eyes and reach for that object. Chances are you have no difficulty grabbing the pencil.

This is a remarkable feat. Your brain continually updates where it believes you are in the world, including where your hand is in relation to the rest of you. It holds the same understanding of where the pencil is. When you grab the pencil, the brain compares the start location (where it thinks your hand is now) with the goal location (where the pencil is), and uses that comparison to activate the correct muscles that move your arm to the desired location next to the pencil.

If you do not stand in awe of this simple ability, watch a baby feed itself with a spoon. A baby does not fully understand where anything is: his food, his mouth, the spoon. As a result, most of the meal winds up on the floor (or his face).

Nor does this ability come from our vision. Perform the same experiment (with your eyes closed again), but move somewhere new before grabbing the pencil. Relative to your body, the pencil is now in a totally different location, requiring a totally new motion from your hand. But chances are your mind still has little difficulty determining the location of the pencil. Or, if a friend snaps his fingers with your eyes closed, you can reach out and grab his hand straight away.

Granted, our mind does the input we receive from our eyes to construct an understanding of the world. Still, what our eyes “see” is only superficially related to what our mind “sees”. The bulk of what we experience is a personal holodeck or virtual-reality that our mind has created for us to live inside. When you close your eyes right now, you can still see the keyboard, monitor and mouse before you — although far less vividly for most people than with open eyes.

Should you or someone else move the mouse, your mind does not receive a new picture of the world projected onto a screen inside your mind like a movie camera does. Instead you see a mouse, and you see that it is moving at a certain speed. Your mind then updates the mouse object inside your virtual reality so that it moves at the correct speed. This is the same way programmers give life to objects with a game or animation engine.

This is how you can watch a moving car disappear behind a building, follow it along behind the building and know exactly when and where it will reappear, even though your eyes see none of this. The car object continues to exist and move inside your head even after your eyes stop seeing it.

Infants are not born with this ability. If you hide an object under one of three cups and ask him where it is, he will simply guess. In fact, a young enough infant will lose track of an object as soon as it is partially obscured. It magically “reappears” when the obstruction is cleared; the infant will giggle with surprise and delight. In America we generally call this game “peek-a-boo”.

It is not an abstraction to say your mind dedicates specific areas of the brain to motion detection and processing. People have strokes in this area. These people see the world just fine — they can close their eyes and describe the contents of their surrounding just as well as we can — but everything they see remains still. If they look at a street, the parked cars look the same as the ones rumbling down the road. They cannot pour coffee: the cup is empty one moment, overflowing with coffee the next. If you have ever played a 3D game on an old computer that can only render one or two frames per second, you can begin to understand the everyday conditions they must endure.

You do not see or experience any true reality. You create a fictitious world (with varying amounts of input from the things you experience) and live inside this.

The implications of this are profound. There is no difference — Psychologists and Neurologists have yet to find one anyway — between dreaming or imaging something from happening and it “actually” happening. When you close your eyes and imagine moving the mouse, your brain responds in exactly the same way it would if you actually did so. The only way your mind knows the difference is that normally you wake up from or snap out of your dreams. The mind reconnects to your eyes, ears and other senses, realizes the mouse never really did move and creates a new “reality” with this updated information.

People with amputated limbs will sometimes fail to update this reality. Even though we can see the person no longer has an arm, when he looks, he sees his arm and hands the same as ever. Ask him to wiggle his fingers and he will do so. These people are not simply lying. Their brains really believe they are wiggling their fingers; they activate the same parts of their brain that a person with fingers we can see do. If these people are holding a coffee cup and you quickly grab the cup out of their non-existent hands, they will experience the same real pain anyone else would in that situation.

What is going on is that these people’s minds do not update their inner-reality. Like most of us, they created and live in a reality where they have two arms and two legs. They close their eyes and — like us — know exactly where their hand is. For their whole lives, they have opened their eyes and their hand right was right where it should. Suddenly, this no longer happens. They open their eyes; their eyes fail to find the hand. They face a dilemma: either their eyes or mind is lying, despite both having a history of being right.

Most people choose to believe their eyes. Their mind abandons its old reality and constructs a new one to replace it. These people close their eyes and (generally) no longer see their missing hand.

A few people refuse to give in. They see their hand as healthy as ever, whether their eyes are open or closed. They know exactly where it is, whether it is waving or holding cup. They simply ignore what their eyes tell them.

Before you think this sounds weird, realize that we do the same thing. We hear screams that our mind decides is “just the wind” and monsters that turn into “just shadows of the trees”. But before we made that the decision, the screams and monsters were as real as anything inside our mind.

When people claim to see space ships or big-foot, I agree with what Ramachandran says in his book, Phantoms in the Brain: they saw a space ship as clearly as they saw the person next to them. Whether their mind gave in to their eyes, their eyes gave into their mind, or the space ship really existed is irrelevant. The space ship is real in their mind.

Question: can people with damaged motion cortexes dream or imagine motion?

Question: if you show someone who sees a phantom limb a photograph of himself, does he still still see his missing-limb in the photograph?

This entry was posted on 2006-9-21 at 22:48 and is filed under Psychology. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.