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Published online 22 December 2008 | Nature | doi:10.1038/news.2008.1328
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Blind man walking
Man navigates obstacles he can't consciously see.
A man with brain damage that makes him clinically blind can navigate an obstacle course, seemingly by using a primitive part of his brain to perceive the objects in his path.
This remarkable ability, discovered through a chance observation, is shedding light on a curious phenomenon known as blindsight.
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Billions of neurons, roughly 1000 muscles and 100 joints are involved in everyday movements. Even with all the senses intact, it would be impossible to control and coordinate such a complex system if the brain were aware of all the 'signals' impinging on it. Besides displaying interesting phenomena TN may be helping scientists become aware of their assumptions.
The article states, "They used brain imaging to show that there was no activity in his visual cortex..." Does the same brain imaging show where there might be activity in response to the stimuli used to test visual cortex function? Since TN's eyes and optic nerves are intact, one might expect activity in the tectum (superior colliculus) and the thalamus (esp. the lateral geniculate nucleus); it is in these regions where vertebrates with no visual cortex (e.g., frogs) have their visual centers. Like other functions normally controlled by the neocortex, midbrain and lower centers continue to function "under the radar", but presumably can function independently when the neocortex is disabled.
one of the arguments that creationists have used against evolution is the existence and de novo development of complex organs such as the eye and the ear. I can't describe it very well, but it seems to me that the existence of this phenomenon which is probably inherent in all ..would aid in the support of slow evolutionary changes to complement and improve on it with the final result being the eye
Some remarks, it is possible to have light sensitivity by means of a melanopsin pathway (intrinsically photosensitive retinal ganglion cells) which project to LGN, SCN and many other earea's in the brain, see Hattar S et all, J Comp Neurol 2006 jul 20;497(3):326-49 and references. it is further possible that by means of "sparing" braincells obtain new functions to make input functional again. The melanopsin pathway can be checked by checking the pupil reflex. FMRI will probably not pick up these kind of signals. Furthermore the patient should be checked for circadian responses; is there a "free running rythm" in this patient and does his rhytm respond on paseshifting light stimuly? Bos NP, The Netherlands
Work by Targ and many others demonstrates that we have an ability to tap into a "field" of quantum energy. An everyday example is feeling the presence of someone in a room without knowning someone is there. So called psychics who are adept at ESP and remote viewing also tap into this field. I think the 21st century will open this sphere to a level of widespread legitimacy within mainline science. We've got a long way to go in understanding and using the full potential of our brains.
Dacey et al in Nature showed that the melanopsin pathway does contribute to visual perception in some way but the retinal ganglion cells have low resolution compared to rods and cones so the contribution here is indirect (either colour constancy or object segregation, say). Dkhissi-Benyahya et al 2006 reports that there are also melanopsin containing cones but no-one else has confirmed or disconfirmed this yet but their sparseness means that are probably either non-imaging or low-resolution as with Dacey et al (and I note in passing that everyone, including the Guler et al paper in Nature earlier this year, appears to be ignoring D-B et al). Of more significance I suspect is that the visual cortex has two main divisions - the ventral pathway where we consciously perceive things, and the dorsal pathway, which we are not conscious of, but which is involved in spatial perception and motor action planning. TN ability is either subcortical (via the superior colliculus and pulvinar nucleus) or its extrageniculate. Its known that the superior colliculus and pulvinar project to the dorsal pathway and information can therefore pass from the retina to the dorsal visual cortex without V1 or the ventral pathway ever knowing about it. See the paper by Perenin & Rossetti (1996) for another example of this.
Can TN negotiate the obstacle course in the dark? That should be a good test to see whether he is using echo-location.
A correction needed? The article states ``TN was not blindfolded to block out all visual input at any stage of the test, "so it can't be ruled out that he was using the echo of the sound of his own breathing or footsteps".'' Clearly, instead than blindfolding, ear plugs or equivalent would be needed to block echolocation and so-called "facial vision" (which is also mediated by auditory input).
This is very interesting !! I've just put down the book called "On Intelligence" by Jeff Hawkins (highly recommended), from which I learned the hypothesis that all sensory areas of our cortex follow the same algorithms. The level below the cortex connecting to our "senses" may process information differently, but when it comes to the cortex, all signals are the same. Now his hypothesis appears to fit with this case, because (1) even though TN's visual cortex was damaged, but the fact that his eyes being OK makes visual signal entering the cortex remain undamaged (2) given enough exposure, the brain then learn to handled such signal at other areas of the cortex, giving TN the same perception of vision. Now the (2) point is pretty speculative, and admittedly difficult to prove, but the ideal of it is very appealing. If it were true, what would TN "feel" different? Would he learn to "see" the world again just like a child does ? (Disclaimer: I don't work on anything biology-related)
You must be kidding me. How could Current Biology publish this work? Nothing quantitative, no controls. It would have taken 5 minutes to put a blindfold on this man to see if he negotiated the obstacle course any differently. In fact they probably did that, found that he tripped over everything, and realized that obviously he has some vision, conscious or unconcious, that kept him from tripping on it in the first place. Or will that be their next paper?