Time is of the essence

New Scientist has an excellent article on how the brain makes sense of time and looks at why certain intense experiences seem to trigger the perception that time has slowed down.

It covers David Eagleman’s well-known study where he dropped people 30 metres into a safety net and while falling, asked them to read off numbers that were flashing by too fast for normal perception.

The idea was that if time really did ‘slow down’, or rather, if the brain became ‘over-clocked’ and the resolution of time perception genuinely became more fine-grained, the participants could read off some of the digits that they couldn’t normally make sense of. As it happened, they couldn’t, suggesting that time slowing effect is an illusion and not an effect of the brain going into overdrive.

The piece also has an interesting discussion of how cognitive scientists are using the wagon wheel effect to study time perception in the brain. This is where after a certain speed, spokes on a wheel seem to starting moving backward.

This has been used to work out the brain’s ‘refresh rate’, but it turns out that this is unlikely to be a global process because when looking at two such objects moving at exactly the same rate, only one of them might be subject to the effect.

This suggests that the brain might have many clocks, perhaps each assigned to a different task:

The case for discrete perception is far from closed, however. When Eagleman showed subjects a pair of overlapping patterns, both moving at the same rate, they often saw one pattern reverse independently of the other. “If you were taking frames of the world, then everything would have to reverse at the same time,” says Eagleman.

VanRullen has an alternative explanation. The brain processes different objects within the visual field independently of one another, even if they overlap in space, he suggests. So the RPL [right inferior parietal lobe] may well be taking the “snapshots” of the two moving patterns at separate instances – and possibly at slightly different rates – making it plausible that the illusions could happen independently for each object.

This implies that there is not a single “film roll” in the brain, but many separate streams, each recording a separate piece of information. What’s more, this way of dealing with incoming information may not apply solely to motion perception. Other brain processes, such as object or sound recognition, might also be processed as discrete packets.

Link to NewSci piece ‘Timewarp’.

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