PLoS One的文章有些还是很不错的，看这篇－－ - 未名空间MITBBS历史存档

PLoS One的文章有些还是很不错的，看这篇－－# Biology - 生物学

u*c2011-02-24 08:02

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first year
no cap
这个卡有没有陷阱？

O*e2011-02-24 08:02

2 楼

Researchers convince people they have three arms--then threaten one with a
knife [Video]
http://www.scientificamerican.com/blog/post.cfm?id=need-an-extr
A knife-wielding researcher is bearing down on your right hand梠r is it
your hand? You see three arms in front of you, and you can feel your pal
ms dampen with fear-induced perspiration. But is it your right hand the
kitchen knife is plunging toward, or a false, rubber right hand?
The dilemma might sound ridiculous, but tell that to the 154 healthy adu
lt volunteers who found themselves persuaded into feeling like they real
ly did have three arms. Their uncanny ordeals are detailed in a study pu
blished online February 23 in PLoS ONE.
The rubber-hand illusion has been a popular perception experiment for mo
re than a decade. In it, a research subject's real hand is hidden from v
iew while a fake rubber hand is substituted in plain sight. Both hands a
re simultaneously stroked with a brush until the person's mind has come
to perceive the fake hand as part of their body. In some people梕special
ly those prone to a poorly developed body schema梩he real hand then star
ts to get ignored by the brain, marked by a discernable temperature drop
. The concept has also helped some amputees alleviate pain in phantom li
mbs.
But the false-hand illusion has been based on the notion that the brain
is maintaining a normal, symmetrical body plan: two arms, two hands. A s
trange new study throws that model out the window梠r at least adds on a
new twist. Researchers at the Karolinska Institute in Stockholm, have sh
own these healthy adults could easily be tricked into feeling as if they
had three arms.
This sensory legerdemain was accomplished by placing a false rubber righ
t hand (matched to the subject only in gender) on a tabletop next to the
subject's real right hand (with the two index fingers approximately 12.
5 centimeters apart). A cloth covered the lower arm up to the shoulder t
o obscure which hand might actually be connected to the body. With the l
eft hand also on view, an experimenter stroked each right hand in parall
el with a small brush.
"What one would expect is that only one of the hands is experienced as o
ne's own, presumably the real arm," Arvid Guterstam, of the Institute's
Brain, Body and Self Laboratory and co-author of the paper, said in a pr
epared statement. "But what we found, surprisingly, is that the brain so
lves this conflict by accepting both right hands as part of the body ima
ge, and the subjects experience having an extra, third arm."
Guterstam and his colleagues then tested the extent to which subjects ha
d adopted this supernumerary limb. After convincing the subjects that th
e third hand was indeed part of their body with the brush strokes, the e
xperimenter then swiftly picked up a kitchen knife and swiped it toward
one of the right hands. A skin conductance response sensor on the left h
and was used to detect any flashes of fear-based sweat in response to bo
dy threats. Sure enough, sweat glands became active when the knife swept
toward the rubber hand as well as when it was approaching subjects' rea
l right hands (even after controlling for any general fear-response upon
seeing the knife), showing that the participants had not disowned their
real hand as happened in traditional rubber-hand experiments.
The new findings are more than just an odd appendage to the rubber-hand
illusion, though. Presumed to be relatively hardwired梑y the nervous sys
tem and a lifetime of experience梩o expect and accommodate two arms, the
human body (and our somatosensory cortex) might be far more flexible in
what it perceives as part of itself. As the researchers noted in their
paper, the results show that, "the body representation can easily be upd
ated to incorporate an additional limb." (Previous research has also sho
wn that the brain starts to incorporate a hand-held tool, such as a hamm
er, as part of its body schema.)
The mind isn't entirely dupable, though. Exchange the false second right
hand for a left hand梠r a prosthetic foot梐nd the brain isn't buying it
. No amount of brush stroking and knife waving could trick the participa
nts into sweating that a chest-level foot was about to lose a toe.
And the researchers contend that there might be applications of this phe
nomenon beyond laboratory trickery. "It may be possible in the future to
offer a stroke patient, who has become paralyzed on one side of the bod
y, a prosthetic arm that can be used and experienced as his own, while t
he paralyzed arm remains within the patient's body image," Henrik Ehrsso
n, also of the Karolinska Institute and co-author of the study, said in
a prepared statement.
And what about those of us who could just occasionally use an extra hand
? "It is also conceivable that people with demanding work situations cou
ld benefit [from] an extra arm," Ehrsson said. But as even the researche
rs pointed out, it's unclear whether the real right hand has to know wha
t the fake right hand does梠r whether the brain would be able to tell th
em to reach for different condiments.