Blind Man Navigates Obstacle Maze Unaided 191
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 eyes are fine (Score:4, Informative)
Re:Ben Underwood (Score:5, Informative)
TFA specifically states that they ruled out echolocation.
Re:his eyes are fine (Score:5, Informative)
"Without a working visual cortex, nothing from the eyes enters the brain. At all."
Whoopsie. Apparently you didn't know about the body of work showing that there are connections between the retina and subcortical areas as well as the striate cortex. Of course, if you'd read the article, you would have noticed they mentioned that.
Yes, I read your other comments, including the one where you claim to have read the article. To summarize: you don't think it's possible... because .
Uhno (Score:5, Informative)
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.
Re:his eyes are fine (Score:5, Informative)
Maybe the problem is that TFA tried to make the science more approachable to people, but you obviously don't understand a single thing about blindsight. This is nothing new at all. In layman's terms, the participant still experiences visual sensation but not visual perception -- they can still see, but they are unaware of it. What is significant in this case is the extent of the damage to the visual cortex. The sensory compensation of congenitally blind people is incredible, but this is an entirely different phenomenon.
Sight doesn't "occur" in the eyes, but there are a number of subcortical structures the information passes through before it gets to the visual cortex. Which, oddly enough, is exactly what they say in TFA, which you claim to have read. They specifically say that the "visual areas of the brain" did NOT "light up", so I have no clue what you're babbling about.
The entire point of the article is that the extent of subcortical visual processing (which we are unconscious of) is greater than most people realise. So feel free to read it again and appreciate what is actually a well-established neurological phenomenon.
Registration required (Score:5, Informative)
From bugmenot.com [bugmenot.com]:
Username: arizonafrank
Password: poochie
Blindsight, Deafhearing and Alien Limbs (Score:5, Informative)
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.
Re:Ben Underwood (Score:1, Informative)
.
Congratulations, you found the point of the article. Many have failed to do so.
Video of the experiment - from BBC (Score:5, Informative)
http://news.bbc.co.uk/2/hi/health/7794766.stm [bbc.co.uk]
Ps: Found this after 'Submit'ting to slashdot
Re:Its not that hard (Score:5, Informative)
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 [gnome.org] was very sluggish and crashed. I guess Slashdot hates blind Linux users.
Video at NPR (Score:2, Informative)
A video of the blind man walking down the corridor accompanies this story at National Public Radio [npr.org].
Re:his eyes are fine (Score:5, Informative)
http://www.amazon.com/Physiology-Behavior-MyPsychKit-Neil-Carlson/dp/0205593895/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1230187013&sr=8-1 [amazon.com]
Chapter 1 has a short item on blindsight and it's relation to consciousness. You should really read chapter 1 of this book.
IMHO, sight doesn't happen as much in the eyes as it does in the brain.
Well, that's how the brain does its thing. Your eyes, ears, nose, skin, are instruments that extend from the brain. Data that flows from your senses to your brain lacks meaning until the brain processes it.
A few posts earlier you say:
( http://science.slashdot.org/comments.pl?sid=1072951&cid=26228425 [slashdot.org] )
Without a working visual cortex, nothing from the eyes enters the brain. At all.
Blindsight does not imply that the visual cortex does not "work". Have a look at http://en.wikipedia.org/wiki/Primary_visual_cortex [wikipedia.org]
Data still flows from the eyes over the optical chiasm to the primary visual cortex (the cortex around the calcarine fissure in the occipital lobe). From there, there are multiple "streams" of visual data. One of those streams is the one that "enters" consciousness.
It is the absolute certainty with which you refute the previous, and the postulation of the following near-superhuman senses that make you appear rather uninformed and quite arrogant.
Most likely, he is using sound or air pressure. Blind people can often maneuver by hearing things like subtle changes in sound of footprints, etc., echoing off of or being aborbed by walls, etc. There are also subtle changes in air pressure as you approach obstacles, and that can often be 'felt' by blind people.
Take a biological psychology course or your own medicine (your signature)
http://www.scholarpedia.org/article/Blindsight [scholarpedia.org]
http://en.wikipedia.org/wiki/Blindsight [wikipedia.org]
Re:his eyes are fine (Score:5, Informative)
Re:his eyes are fine (Score:4, Informative)
If you RTFA (I know, a big assumption -- Google can take you to the no-registration-required SciAm version), they say that scientists suspect there are other pathways where the info is getting into his brain, even though his visual cortex is totally destroyed on both hemispheres. This is the first blindsight demo with NO visual cortex, and thus seems to suggest strong that there are some alternate pathways going on. He can also react to facial expressions.
Re:his eyes are fine (Score:3, Informative)
The signal from the optic nerve doesn't go exclusively to the primary area of the visual cortex- it forks at the lateral geniculate nucleus before it gets there and some also goes to subcortical targets which provide functions like the flinching reflex. These are older pathways and modern vision evolved by eavesdropping on the signal.
Re:Its not that hard (Score:2, Informative)
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.
Re:Its not that hard (Score:3, Informative)
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.
Re:Its not that hard (Score:2, Informative)