Stereo-Sue as a Real Life Problem Of Problem of Mary


            In chapter 5 of his 2010 book ‘The Mind’s Eye’ neuroscientist Oliver Sacks discussed the case of Sue Barry, a lady who grew up cross eyed and whose eyes did not work in tandem, so she had to view things one eye at a time. As a result of her condition she was unable to view the world stereoscopically, so she lacked the ability to see the world in the same three dimensional manner normal people do. Sue was a neurobiologist who had read the works of Hubel, Wiesel and many other scientists on stereo vision. In 1996 at a shuttle launch party she met Oliver Sacks and discussed her lack of stereo vision with him. He asked her if she could imagine what it was she was missing as a result of lacking stereo vision. She said that yes she could because her knowledge of neurobiology helped her understand what the experience of stereo vision would be like. In 2004 Sue sent a letter to Sacks to inform her that she had treatment on her eyes and now had stereopsis. She noted the following about her experience of stereo vision:

You asked me if I could imagine what the world would look like when viewed with two eyes. I told you that I thought I could… But I was wrong”

            Now clearly Sue’s case has a lot in common with Frank Jackson’s thought experiment ‘The Problem of Mary’. In Jackson’s thought experiment Mary is a neuroscientist who knows everything about the physics, and neurobiology of colour vision. However she has been brought up in a black and white room so has absolutely no experience of colour. One day she released from her black and white room and she experiences colour for the first time. A substantial proportion of philosophers have argued that after being released from her room, she will be in awe of her experience of colour which will go beyond anything she could have predicted on the basis of her complete knowledge of third person science. So they argue that there are experiential facts which are not captured by a complete scientific understanding.

In some ways one could argue that Stereo-Sue is a real life Mary who supports the conclusion that there are experiential phenomena e.g. qualia which cannot be captured by third person science. However there are obvious disanalogies between the two cases. The most important one being that in the case of Mary it is stipulated that she has ALL of the scientific knowledge of colour while Sue on the other hand is an extremely well educated neuroscientist who obviously doesn’t know everything about the neuroscience and physics of stereo-vision.

Dennett has critiqued ‘The Problem of Mary’ thought experiment as being a simple intuition pump where the conclusion is more or less stipulated. He argues that one could just as easily draw the opposite conclusion that upon leaving the room Mary is not surprised because given that she knows all of the science she will know what the experiential facts will be like. Dennett’s point is that one can stipulate how Mary will react all we want, however the truth is we do not know how we she will react. The thought experiment is merely designed to make it seem plausible that there will be experiential facts which third person science cannot capture. However the thought experiment proves no such thing.

Now in the case of Stereo-Sue because she is a real person she obviously doesn’t know everything. So we cannot draw any conclusions as to whether knowing all of the relevant scientific fact about stereo vision would have enabled her to predict what the experience of stereo vision would be like. In Sue’s case the amount of scientific knowledge she had wasn’t enough for her to predict what her experience would be like if she had Stereo Vision. However it tells us little about whether she would have been able to predict accurately what the experience of stereo vision would have been like if she knew more third person science or if a la Jackson she knew all of the third person science. So clearly Stereo-Sue’s story has little bearing on ‘The Problem of Mary’.

Nonetheless the case of Stereo-Sue has led Oliver Sacks drawing the following dramatic conclusion:

She had discovered for herself that there is no substitute for experience, that there is an unbridgeable gulf between what Bertrand Russell called “knowledge by description” and “knowledge by acquaintance,” and no way of going from one to the other” (The Mind’s Eye, p. 131)

Sack’s view of the case of Stereo Sue is similar to that of people like Tom Nagel. Sacks thinks that her case demonstrates an unbridgeable gap between what we can know from third person science and what we can directly experience. However, there is no reason to draw the dramatic conclusion that Sacks does. Granted some of Sue’s descriptions are extremely interesting and extremely dramatic, she reports the following experience after a session with her developmental optometrist:

“I went back to my car and happened to glance at the steering wheel. It had “popped out” from the dash-board. I closed one eye, then the other, then I looked with both eyes again, and the steering wheel looked different. I decided that the light from the setting sun was playing tricks on me and drove home. But the next day I got up, did the exercises, and got into the car to drive to work. When I looked at the rear-view mirror, it had popped out from the windshield.” (ibid, p. 128)

“Today, I was walking by a complete horse skeleton in the basement of the building where I work, when I saw the horses’ skull sticking out so much, that I actually jumped back and cried out.” (ibid, p, 130)

Sue’s experiences are extremely interesting however they do not support Sack’s conclusion. If Sack’s wants to point to an unbridgeable chasm between experience and knowledge he will need a real life case of Mary. This will obviously never happen as it is extremely unlikely that humans will ever have a completed knowledge of the physical world.

Now Stereo-Sue could be used as a part of a kind of inductive argument. If we could discover a variety of different cases that of scientists who had similar impairments and who after an operation discovered experiences that they could not predict from their science. It could be argued that this is inductive evidence that in Mary’s case she is likely to be surprised as well. However such an argument would be extremely weak as there is no reason to think that a person with ALL scientific knowledge will have predictive powers even remotely analogous to those of contemporary scientists. Therefore the inductive argument fails.  So over all, it seems that despite what Sacks thinks there is no reason to think that Stereo-Sue case provides an unbridgeable chasm between experience and knowledge. It is unbridgeable for us today, but may not be for Mary.


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