Wednesday, November 24, 2004

Sensory Substitution

This is fascinating stuff:
Ms. Schiltz and other patients like her are the beneficiaries of an astonishing new technology that allows one set of sensory information to substitute for another in the brain.

Using novel electronic aids, vision can be represented on the skin, tongue or through the ears. If the sense of touch is gone from one part of the body, it can be routed to an area where touch sensations are intact.
[T]he brain does not seem to care if patterns come from the eye, ear or skin. Given the proper context, it will interpret and understand them. "For me, it happened automatically, within a few minutes," said Erik Weihenmayer, who has been blind since he was 13.
He found doorways, caught balls rolling toward him and with his small daughter played a game of rock, paper and scissors for the first time in more than 20 years. Mr. Weihenmayer said that, with practice, the substituted sense gets better, "as if the brain were rewiring itself."
Dr. Ptito is scanning the brains of congenitally blind people who, wearing the BrainPort, have learned to make out the shapes, learned from Braille, of capital letters like T, B or E. The first few times they wore the device, he said, their visual areas remained dark and inactive - not surprising since they had been blind since birth. But after training, he said, their visual areas lighted up when they used the tongue device.

I find this to be an incredibly exciting topic. It's a pity the NY Times article doesn't tackle some of the most interesting questions raised by such research. E.g. What do these new sensations seem like, in the subject's consciousness? Are these people actually seeing? Are they just receiving information about visible things (size, motion, distance, etc) in tactile form? Or it is some new conscious quality altogether?

Fortunately, these questions are discussed by Dennett in his book Consciousness Explained. For example, he describes how the subject's "awareness of the tingles on their skin dropped out", and their 'point of view' shifts from the area of tactile stimulation to the position of the camera.
The array of tinglers was on [the subject's] back, and the camera was mounted on the side of his head. When the experimenter without warning touched the zoom button, causing the image on the subject's back to expand or "loom" suddenly, the subject instinctively lurched backward, raising his arms to protect his head. (p.341, original emphasis)

Although suggestive, there's still room to doubt whether these subjects experience genuine visual qualia. Even if scans show activity in the visual regions of their brains, that might just be because they're (subconsciously) processing visual information (size, motion, etc.). I'm inclined to think that, ultimately, the subject is the only expert regarding their own subjectivity. If we want to know what substituted sensations seem like, we need to ask the subjects who are experiencing them. That's why I'm disappointed the article didn't probe a bit deeper regarding this point. The closest they come is with the following comment:
Mr. Weihenmayer said the device at first felt like candy pop rocks on his tongue. But that sensation quickly gave way to perceptions of size, movement and recognition.

But did they seem (qualitatively speaking) just like normal visual perceptions? We're not told. They're clearly not as accurate or detailed as usual - Mr W. once confused his wife with a tree! So that might affect their subjective quality. It would be especially interesting to hear from someone using a "higher-resolution" device, capable of transmitting as much information as our eyes usually do.

I wonder what would happen if you had two cameras, facing in opposite directions, each wired up to a different tactile area? Could you be trained to develop 360 degree vision? Would you see the images superimposed atop each other (like when you can see a reflection in a glass window)? Or would it just be too confusing to make any sense of at all?

This may be similar to a normal-sighted subject receiving a single sensory substitution. Such a situation is (all too briefly) described in the article:
Dr. Raj said the tongue unit had already been tried out in a game that involved shooting villains. "In two minutes you stop feeling the buzz on your tongue and get a visual representation of the bad guy," he said. "You feel like you have X-ray vision. Unfortunately it makes the game boring."

Is it superimposed - is that what he means by "like... X-ray vision"? How is that boring? Argh, so many unanswered questions...

1 comment:

  1. I have a blog post on this exact same thing, although might have read a different article.

    Does anyone know if this guy's firsthand papers are available to read? i.e. Free, free and freely? If not, does anyone have a good knowledge of electronics, a few hundred bucks and a willing slave?


    Posted by Tennessee Leeuwenburg


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