I think this is extremely important in our understanding of a whole
range of skills were reaction becomes preternatural. Several clocks are integrated but this can
also be selected for. The quick lesson
is that key skills need to be made autonomous.
Thus a long ritual in order to aim a long bow may well be seriously
counterproductive while a simple draw and shoot is far easier to train up. One still needs to master all the movements
but the objective must be to make them automatic.
Up until now, we worked under the assumption that it all tied together
somewhat independent of our training protocols.
Now it is suggested that real options exist.
First man to hear people before they speak
10:49 04 July 2013
by Helen Thomson
"I told my daughter her living room TV was out of sync. Then I
noticed the kitchen telly was also dubbed badly. Suddenly I noticed that her
voice was out of sync too. It wasn't the TV, it was me."
Ever watched an old movie, only for the sound to go out of sync with
the action? Now imagine every voice you hear sounds similarly off-kilter – even
your own. That's the world PH lives in. Soon after surgery for a heart problem,
he began to notice that something wasn't quite right.
"I was staying with my daughter and they like to have the television
on in their house. I turned to my daughter and said 'you ought to get a decent
telly, one where the sound and programme are synchronised'. I gave a little
chuckle. But they said 'there's nothing wrong with the TV'."
Puzzled, he went to the kitchen to make a cup of tea. "They've
got another telly up on the wall and it was the same. I went into the lounge
and I said to her 'hey you've got two TVs that need sorting!'."
That was when he started to notice that his daughter's speech was out
of time with her lip movements too. "It wasn't the TV, it was me. It was
happening in real life."
PH is the first confirmed case of someone who hears people speak
before registering the movement of their lips. His situation is giving unique
insights into how our brains unify what we hear and see.
It's unclear why PH's problem started when it did – but it may have
had something to do with having acute pericarditis, inflammation of the sac
around the heart, or the surgery he had to treat it.
Brain scans after the timing problems appeared showed two lesions in
areas thought to play a role in hearing, timing and movement. "Where these
came from is anyone's guess," says PH. "They may have been there all
my life or as a result of being in intensive care."
Disconcerting delay
Several weeks later, PH realised that it wasn't just other people who
were out of sync: when he spoke, he registered his words before he felt his jaw
make the movement. "It felt like a significant delay, it sort of snuck up
on me. It was very disconcerting. At the time I didn't know whether the delay
was going to get bigger, but it seems to have stuck at about a quarter of a
second."
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
normally perceive the events as happening simultaneously – but how the brain
achieves this is unclear.
To investigate PH's situation, 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 37 others were
tested on both tasks, many showed a similar pattern, though none of the
mismatches were noticeable in everyday life.
Many clocks
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 have happened too
suddenly for him to ignore or adapt to, 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.
PH says that in general he has learned to live with the sensory
mismatch but admits he has trouble in noisy places or at large meetings. Since
he hears himself speak before he feels his mouth move, does he ever feel like
he's not in control of his own voice? "No, I'm definitely sure it's me
that's speaking," he says, "it's just a strange sensation."
Help may be at hand: Freeman is looking for a way to slow down PH's
hearing so it matches what he is seeing. PH says he would be happy to trial a
treatment, but he's actually not that anxious to fix the problem. "It's
not life-threatening," he says. "You learn to live with these things
as you get older. I don't expect my body to work perfectly."
Journal reference: Cortex, doi.org/m3k
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