The Illusion of Time

The Edge has an article describing research into how the brain reconstructs the passage of time from imperfect clues from the senses.

This is the problem of temporal binding: the assignment of the correct timing of events in the world. The challenge is that different stimulus features move through different processing streams and are processed at different speeds. The brain must account for speed disparities between and within its various sensory channels if it is to determine the timing relationships of features in the world.

Think about that for a second. There are all these message that get jumbled up and arrive out of sequence. Somehow your brain tries to figure out what order they should be in. How does it do that?

It guesses.

When it comes to awareness, your brain goes through a good deal of trouble to perceptually synchronize incoming signals that were synchronized in the outside world. So a firing gun will seem to you to have banged and flashed at the same time. (At least when the gun is within thirty meters; past that, the different speeds of light and sound cause the signals to arrive too far apart to be synchronized.)

But given that the brain received the signals at different times, how can it know what was supposed to be simultaneous in the outside world? How does it know that a bang didn’t really happen before a flash? It has been shown that the brain constantly recalibrates its expectations about arrival times. And it does so by starting with a single, simple assumption: if it sends out a motor act (such as a clap of the hands), all the feedback should be assumed to be simultaneous and any delays should be adjusted until simultaneity is perceived. In other words, the best way to predict the expected relative timing of incoming signals is to interact with the world: each time you kick or touch or knock on something, your brain makes the assumption that the sound, sight, and touch are simultaneous.

And if it guesses wrong?

Imagine that every time you press a key, you cause a brief flash of light. Now imagine we sneakily inject a tiny delay (say, two hundred milliseconds) between your key-press and the subsequent flash. You may not even be aware of the small, extra delay. However, if we suddenly remove the delay, you will now believe that the flash occurred before your key-press, an illusory reversal of action and sensation. Your brain tells you this, of course, because it has adjusted to the timing of the delay.

Think that’s weird?

Wait until you find out how long it takes for your brain to figure this stuff out. And what it does before it has all the information in.

What would it be like if you brain lost the ability to order events correctly? Read the article and find out.

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Ragged Clown

Based in San Jose, California

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