Comments on: Blind man navigates obstacle course perfectly with no visual awareness

By: Azrael Brown

Azrael Brown — Sat, 27 Dec 2008 16:00:07 +0000

When I was younger I’d get slight migranes; not much pain, but I’d see sparkles around the edge of my vision, which would slowly grow until they blocked my entire eyesight (I’ve heard them called “optic migraines”). I’d just have to sit and rest or nap and they’d go away. One particular time I had one and was unable to “see” at all due to sparklies in my vision, but someone handed me a glass of water and I grabbed it without thinking; I briefly experimented with ‘seeing’ and found that, the less I concentrated on what I was doing, the better I did (the more I did, the dizzier I got, so I didn’t do it long). It really shows how “me” and “my body” tend to be two things operating cooperatively, not necessarily one-and-the-same.

By: Dr X

Dr X — Tue, 23 Dec 2008 21:55:46 +0000

It would, indeed, be interesting to hear what TN has to say. I did find this general claim, on the subject:

It is particularly important that blindsighted persons describe themselves as not seeing anything within their blind fields, and as not having any knowledge about the objects presented there. Hence, from their perspective they are only guessing, when they are forced by the insistence of the experimentator to make decisions between given alternatives. What is amazing about blindsight, is the fact that there is a significant contrast between the declarative and the procedural knowledge of the blindsighted persons.-- link

But, the hallway obstacle course isn't a task involving forced choice between given alternatives. I wonder if TN was simply asked to walk with the additional instruction "try to avoid any obstacles as you walk." I found this speculation from another article interesting:

The admission of a realm of agentic qualia makes the story I have been telling considerably more complicated. But that's a good price to pay for making it more likely to be right. One particular area, I might mention, in which it makes it more likely to be right - and indeed makes it possible to tell a story at all - is in relation to the much-disputed phenomenology of blindsight. Suppose that, despite the fact a person with blindsight has no consciousness of visual sensations in the blind field, he nonetheless does experience it as "like something", consciously, to detect an object in the blind field (and several reports suggest that in a strange way it may be so) - then perhaps the explanation is that what he is experiencing are the agentic qualia associated with his having an incipient plan to grasp the object. -- link

By: TM

TM — Tue, 23 Dec 2008 19:59:28 +0000

Has any one thought to ask TN how he does it?

By: Ed Yong

Ed Yong — Tue, 23 Dec 2008 15:16:26 +0000

While it’d be interesting to read about how he felt while navigating the corridor, I actually wonder how informative that might be. I think the idea is that whatever pathways he’s using lie outside conscious thought – he is, after all, functionally blind and has no conscious awareness of seeing. He doesn’t have any other cognitive problem, by the way – just the blindness.

By: Noni Mausa

Noni Mausa — Tue, 23 Dec 2008 15:09:07 +0000

What I looked for in the article, but didn’t see, was a report of that the patient himself thinks about this. Unless his speech has been badly affected, he should have some interior report which might add to the topic.
Noni

By: Ed Yong

Ed Yong — Tue, 23 Dec 2008 09:26:41 +0000

Thanks for the context folks. I did feel that the paper was frustatingly conservative in suggesting possible explanations/pathways but that’s an emotional reaction from me – as Michael said, I fully understand the reasons for being cautious.
Psycho – I think the objection to the echolocation idea is that it’s unlikely that it could provide enough spatial resolution to be able to avoid some of the smaller obstacles like the boxes. In the example you cite of someone standing behind you, a person is considerably larger than any of the obstacles TN bypassed.

By: Michael Anes

Michael Anes — Tue, 23 Dec 2008 02:16:04 +0000

If I recall my blindsight literature correctly (and I haven’t read this report yet) I thought for sure that there are identified pathways directly from the thalamus to motion area V5 (or called MT). Not mysterious. But if so, these are better abilities than have been demonstrated before.
Now I have to go read!

By: Michael MacAskill

Michael MacAskill — Tue, 23 Dec 2008 00:40:31 +0000

This is not perhaps as entirely mysterious as your entry implies. The paper gives a nicely characterised case, particularly by using DTI imaging to track white matter pathways and show the extent of the damage, which wasn’t available for earlier case reports. But blindsight and related effects are well-established phenomena, with Larry Weiskrantz, one of the co-authors of this paper, being particularly prominent in this field over several decades.
Just because striate cortex is obliterated doesn’t mean visual information doesn’t reach other parts of the brain. For example, this person will almost certainly still have a pupil reflex. Most visual fibres from the optic tract reach a relay station in the thalamus called the lateral geniculate nucleus and travel thence to striate cortex (which is disrupted in this case). But some fibres directly project directly to the pretectal area in the midbrain which controls the pupil reflex. So it is quite possible for a person’s pupils to constrict in response to light that they don’t report seeing.
Still other fibres travel to another midbrain structure called the superior colliculus, which is capable of controlling much more interesting behaviour. It can generate eye movements to a visual stimulus and cause other orienting movements. There may be a useful ascending pathway from superior colliculus to parietal cortex which controls spatial awareness and directed movement. That cortical area normally gets much of its information from the neighbouring visual cortex but might rely more on other sources when that is not available, as in this case.
The authors are being rightly conservative about naming possible pathways because they don’t have any evidence in favour of any particular one in this case. But candidate pathways are certainly known:
“In addition to the projections to the superior colliculus, the retina projects directly to at least ten other distinct sites in the thalamus, hypothalamus and midbrain and some of these structures send projections in turn to the cerebral cortex. Processing in all or some of these pathways could support many of the different kinds of visually guided behavior that have been called blindsight.” (Danckert & Goodale, 2000. Blindsight: a conscious route to unconscious vision. Current Biology, 10, R64-R67, p. 64)
To rule out the use of auditory information would be reasonably straightforward. Just get the subject to wear an iPod, playing white noise to be scientific, but loud music would suffice.

By: psycho

psycho — Mon, 22 Dec 2008 22:19:37 +0000

Sorry, me again.
Maybe if they could try few things:
- record him going in total dark, using infra camera
- move objects further away from each other, so that you know whether he dodges (or not) because he sensed object on his side, or in front of him (i mean that green book)
- try different shapes with different material (what about flat piece of another carpet?)

By: psycho

psycho — Mon, 22 Dec 2008 22:10:51 +0000

I believe he navigates with sound, using echolocation. It happens to me very often, that I can feel somebody standing right behind me, even though he makes no sound. Its probably because he’s blocking noise coming from behind. It can be very little noise (smaller than from street through good windows, air flowing). It’s like when you cover your ears – you can actually HEAR the silence, its different.
But yeah, could be anything, looking forward for explanation.