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Blind Man Navigates Obstacle Maze Unaided
iammani writes "The NYTimes runs a story about a blind man (blind because of a damaged visual cortex) successfully navigating an obstacle maze, unaided. Scientists have shown for the first time that it is possible for people who are blinded because of damage to the visual (striate) cortex can navigate by 'blindsight,' through which they can detect things in their vicinity without being aware of seeing them."
his brain is still able to make use of the input comming from the eyes which are undamaged. interesting.
If you mod me down, I will become more powerful than you can imagine....
TFA specifically states that they ruled out echolocation.
Always going forward, 'cause we can't find reverse.
This is hardly the first time blindsight has been demonstrated. I recall Ramachandran at UCSD doing experiments on it a while back.
One of the more mind blowing things I read in 2008 was the discovery of a third type of visual receptor besides rods and cones. Essentially there's a third type of receptor that only detects sort of gross levels of light, and feeds directly into the system which regulates your circadian rhythm and is used for some other purposes. People that were completely blind were able to tell when light levels were fluctuated in a large way, like walking in front of a TV, and be totally puzzled how they knew that, since it didn't register as sight at all for them.
The fact that these neuroscientists would call it the first evidence for blindsight means that either they really didn't read their papers very well, or it was a bad article summary on Slashdot.
From bugmenot.com:
Username: arizonafrank
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No existe.
There are two distinct causes of blindsight (and deafhearing and alien limb syndrome), damage to the primary sensory cortext but not the secondary or assosiation cortices, and damage to the association cortex, but not the sensory.
The latter is easy to explain. The person can perceive, but can't incorporate the fact of it into their conscious experience. They can't "own" the perception. This is very often found in damage to the somatosensory cortex which leaves partial paralysis. Often the person can't perceive the limb attached to their body as 'theirs'. Sensations in the limb do not become perceptions for them. Similarly, vison and hearing can occur, and the brain can make use of the data, but the person can't perceive it because it's not coming from "them".
The former is harder to explain. There seems to be a parallel visual (and auditory) system through which information can pass and the brain make use of, but which bypasses the association cortex. The person can't perceive normally, but if tested they react as if they can. They can, for instance, consistently "guess" the number of fingers shown them. There is a similar system for somatosensory. Perception of touch to, say, the hand, has highly detailed "maps" elsewhere on the body. For the hand it's on the cheek and on the back just below the shoulder. Just why this secondary pathway exists is a mystery. But it does, in most people.
Around 20 years ago in Coevolution Quarterly there was an article about a 'school' in (IIRC) New Mexico that taught people to use their blindsight to navigate in the desert at night. The secondary visual pathway that persons with the second form of blindsight use, exists intact in everybody. It's not something you develop because of damage, it's something that's there in case you need it but below the level of consciousness so as not to interfere with normal perception. Occasionaly hunters, hiker/campers or survival technique practioners will hear of a person who can literally run through a pitch black forest without running into anything. These people have the ability to react to the subliminal perception from the secondary visual system in what occurs to them as instinctive reactions because they don't consciously perceive anything.
"I may be synthetic, but I'm not stupid." -- Bishop 341-B
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Congratulations, you found the point of the article. Many have failed to do so.
Heres a video of the man walking through the obstacles - from BBC
http://news.bbc.co.uk/2/hi/health/7794766.stm
Ps: Found this after 'Submit'ting to slashdot
I call it being able to hear the "sound shadows" of objects, because that's really what they are - an object blocks sound, and that blockage is projected to the ear. With a good cane, I can navigate around tables, columns, and even position myself relative to peoples' voices to keep myself from running into them. It's quite amazing what you can tell with a good hallway, and a constant sound source (soda/vending machines are good). For example, an open, echoy space usually means a stairwell.
Also, randomness ... the first time I went to post, my screen reader was very sluggish and crashed. I guess Slashdot hates blind Linux users.
A video of the blind man walking down the corridor accompanies this story at National Public Radio.
The article sure reads like BS, but that's popular science for you. I read about this kind of thing back in first year psychology (never did second year, I don't claim to be an expert). The brain is, frankly, a complete fucking mess from a design perpsective. It's entirely possible to knock out random parts of abilities that would be unitary if the brain was well designed, particularly through strokes or other injuries that damage small parts of the brain exclusively. Speech centres are classic; people lose their nouns, or the ability to speak entirely but can still swear reflexively because the reflex is in a different part of the brain.
I read about this kind of blindsight too, I'm not sure how this case is exceptional except that it's recent news and it's an uncommon condition. It's not magical (except when pop sci journalists need a story), it's just that the brain doesn't store all its functionality in logical places. I forget what the explanation I read was, but most likely the hardware for visually identifying objects is in a different place from the hardware for avoiding objects (regardless of what they are). IIRC, there are edge detecting cells in the eye, so it's plausible that something like a wire frame model gets sent down the optic nerve even before the visual areas get to work on it. There's quite a lot of visual cortex, and I suspect the journalist was glossing over some of the details. As I said, it sounds like BS except for the background I already know.
Fun further experiments: throw balls of rolled up paper at his head and see if he can dodge them; get him to throw things at a target! Both are plausible if he has object-sensation but not object-identification.
.evom ton seod gis eht
While that is true, that's not what's happening here. In the case from TFA, the man is not conscious of any visual sensory input, but IS able to subconsciously make use of visual information. Also from TFA, he has the same subconscious responses to being shown pictures of people's faces displaying various emotions and other responses that cannot be due to echolocation.
In another experiment (not part of TFA) a number of subjects with cortical blindness were able to accurately state which direction a dot of light was moving across a screen at a rate far above chance. It is suggested that they can improve upon their results with practice.
RTFA. Of course he would hit the obejcts. The article states that the person needs working eyes and that the vision he gets is unconcious.