For the past three weeks, we have been talking about the connection between the physical world of the brain and the metaphysical world of the mind. This week, I would like to finish this discussion with two aspects of the mind/brain problem which emphasize the complexity at hand.
The first is the question of time.
If you think about thinking, it will most likely seem to you that it is a continuous thread. One thought flows smoothly into the next. One action follows another.
Our sensations happen at the same time.
However, consider the simple act of getting hit on the toe. We perceive this through our sense of touch as pain. We see our toe being struck through our eyes.
We might even hear the resulting sound of the blow. In our mind, these are simultaneous occurrences. They happen at the same time.
Yet we know it takes nerves signals more than 200 milliseconds to travel from the toe to the brain while the visual signals received by the retina arrive in less than 20 milliseconds. There is almost a two tenths of a second difference between seeing our toe get hit and feeling it.
How do we account for this time discrepancy?
There are a number of theories but the most popular is that we don't live in an instance in time but rather a span of time about 30 milliseconds or so long, under normal circumstances. It can be stretched out even further when the need arrives.
Put another way, if our consciousness was a tape run through a machine, it would constantly be moving back and forth.
We hold time in our mind for moments while we edit the tape to produce a cohesive picture of the world around us.
Psychologists have found a number of ways to test this hypothesis.
With the advent of computer monitors, for example, one experiment presented a series of volunteers with two large flashing dots of color. With the right distance and timing, the dots appear to be a single dot moving back and forth. (Imagine a game of Pong if you can remember it.)
This is not an unusual experimental setup. In many ways, it is how television creates the illusion of motion or what we see on the silver screen. A series of still images, if played fast enough, is stitched together by visual cortex into a continuous scene.
Now imagine one of the dots is yellow and the other is red. What you should see is a yellow dot disappear and a red dot appear.
But because we perceive the dot to be moving from one location to the other, this makes no sense. So instead we see a yellow dot fade into a red dot and then back again as it moves across the screen.
The really tricky part comes into play when experimenters now randomly change the colours of the dots. You still see a gradual shift - one colour fading into the other - but this can happen by as much as 25 milliseconds before the second dot appears. In other words, 25 milliseconds before, say, a green dot actually appears on the screen, you perceive a shift to the colour green.
Your mind is editing your consciousness.
It is "rewinding" the tape and writing your moment of thought to be consistent with what you see.
We do this all the time. Consciousness is not smooth but jerky with re-writes and post-scripts.
However, from the perspective of the mind, this is all happening at the level of zombie systems inside our functional brain. We are not conscious of the processing of our own consciousness.
The second idea is more philosophical in nature. Since you can't know what I am actually experiencing in my mind and I can't know what it is like to you, how do we know we are experiencing the same thing?
That is, we both call the sky blue but do we both perceive it in the same way?
Our minds understand the world as told to us by our senses and we assume everyone's senses work in the same fashion. But we know this is not true.
For example, someone who is colour blind is definitely not going to see the sky in the same way as someone who isn't. Equally, for the 15 per cent of women who have four instead of three types of cones in their eyes - who have four channels of colour information - they see sky blue as something different from the rest of us.
Much of what are senses tell us is therefore socially constructed.
We all see the sky and whatever colour we perceive it to be, we all agree that colour is what we call blue.
In the end, our minds construct our world out of atoms and the void.
