“Its DeJa Vu All Over Again”
The human brain is very much like a computer.
A computer is very much like a clock. Or a series of clocks that are coordinated to keep things happening in order.
What happens when the clockwork gets a little bit offset?
From an article in The New Scientist.
First man to hear people before they speak
EVER been watching an old movie, only for the sound and action to go out of sync? Now imagine every voice is like this – even your own. That’s the world PH lives in.
PH is the first confirmed case of someone who hears people speak before registering that their lips have moved. His situation is giving unique insights into how our brains unify what we hear and see.
Light and sound travel at different speeds, so when someone speaks, visual and auditory inputs arrive at our eyes and ears at different times. The signals are then processed at different rates in the brain. Despite this, we perceive the events as happening simultaneously. How this happens, however, is unclear.
An opportunity to study this process came about when 67-year-old PH started experiencing bad dubbing following surgery. “I said to my daughter ‘hey, you’ve got two TVs that need sorting!’,” he recalls. PH then realised that he was hearing his own voice before feeling his jaw move. A scan of his brain showed he had two lesions in areas that may play a role in hearing, timing and movement.
To investigate, Elliot Freeman at City University London and colleagues performed a temporal order judgement test. PH was shown clips of people talking and was asked whether the voice came before or after the lip movements. Sure enough, he said it came before, and to perceive them as synchronous the team had to play the voice about 200 milliseconds later than the lip movements.
The team then carried out a second, more objective test based on the McGurk illusion. This involves listening to one syllable while watching someone mouth another; the combination makes you perceive a third syllable.
Since PH hears people speaking before he sees their lips move, the team expected the illusion to work when they delayed the voice. So they were surprised to get the opposite result: presenting the voice 200 ms earlier than the lip movements triggered the illusion, suggesting that his brain was processing the sight before the sound in this particular task.
And it wasn’t only PH who gave these results. When 34 others were tested on both tasks, many showed a similar pattern, though none of the mismatches were noticeable in everyday life (Cortex, doi.org/m3k).
Freeman says this implies that the same event in the outside world is perceived by different parts of your brain as happening at different times. This suggests that, rather than one unified “now”, there are many clocks in the brain – two of which showed up in the tasks – and that all the clocks measure their individual “nows” relative to their average.
In PH’s case, one or more of these clocks has been significantly slowed – shifting his average – possibly as a result of the lesions. Freeman thinks PH’s timing discrepancies may be too large and happened too suddenly for him to ignore, resulting in him being aware of the asynchrony in everyday life. He may perceive just one of his clocks because it is the only one he has conscious access to, says Freeman.
Tim Griffiths at Newcastle University, UK, says any interpretation is hard, but that Freeman’s multi-clock theory is possible. As for PH, help may be at hand: Freeman is looking for a way to slow down his hearing so it matches what he is seeing.
It makes me wonder how much this sort of phenomena might explain a wide variety of telepathic or precognitive phenomena.
Maybe all these people should get together an from a band
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