Tuesday, January 20, 2015
Perceptual transparency (repeated as background to next post)
In 1976, when I delivered the John Locke Lectures at Oxford, I often spent time with Peter Strawson, and one day at lunch he made a remark I have never been able to forget. He said, "Surely half the pleasure of life is sardonic comment on the passing show". This blog is devoted to comments, not all of them sardonic, on the passing philosophical show.
Back in August (August 27, 2014, to be exact), my post included a description (which follows) of two sets of experiments by Richard Held of MIT, who was my colleague when I was Professor of Philosophy of Science there from 1961 to 1965. I argued, and would still argue, that those experiments show that what is called the “transparency” of our visual experiences is learned and not innate or intrinsic (not part of their “essence”, as it were). Some months later Held transmitted to me a further description of the second set of experiments (involving children who had been blind from birth) by Pawan Sinha, who collaborated with Held in this research. In this post, I will simply repeat the earlier description so my readers won’t have to scroll down all the way to the August 27 post. In the next post I will give the further description and discuss whether it requires any modifications in my argument.
Held’s experiments (1)
There is strong experimental evidence that in certain cases, described by Richard Held in two different series of experiments many years apart, some non-human mammals and even some humans do not visually perceive colors and shapes as “out there”. I conclude that “transparency” is (normally) the result of early learning (but, contrary to Block’s view, mentioned in my previous post, not something we can override if we try and we know how to do it. At least I see no evidence for this claim.) The first visual experiences of many mammals, including both cats and humans, are not experienced by those organisms as properties of surfaces “out there”. “Out-thereness”, recognition of things as having locations in places accessible to both sight and touch, requires that the correlations between visual space and sensorimotor (tactile, or “haptic”) space be learned. The disposition to learn such correlations quickly may well have been selected for in the evolutionary history of our visual and haptic systems, but some hours or days of learning are still needed. Here is some background.
In 1963, when Richard Held and I were colleagues at MIT, he showed me the following experiment that he and Alan Hein performed: two kittens were placed in baskets that were at the opposite ends of a pole that was free to rotate around a vertical axle. One basket had holes that permitted the kitten in that basket, kitten A, to push against the floor and thus to determine how the basket would move, at least to a limited extent. Kitten B’s basket had no holes; willy nilly, kitten B experienced spatial motion when kitten A moved – the mirror image of kitten A’s spatial motion, in fact - but no sensorimotor feedback. When kitten B was taken out of its basket, it had no recognition of any sensorimotor affordances at all. If one poked a finger towards its eyes, it stuck out its paws (an innate reflex), but not in the direction of the approaching finger. If it were put near the edge of the table, it would fall off (or would have fallen if there were not something to catch it) as often as not. But when Kitten A was taken out, it was able to position its paws in front of the threatening finger, it never walked off the edge of the table, etc. The results strongly suggest that the kitten that had not learned those correlations did not see the visual data it experienced as “out there”, and so the phenomenal aspects of its visual experiences were not transparent.
Held’s experiments (2)
In 1688 William Molyneux sent a message to the philosopher John Locke asking: “Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal ... Suppose then the cube and sphere placed on a table, and the blind man be made to see: query, whether by his sight, before he touched them he could now distinguish and tell which is the globe, which the cube ...?”
In 2011 a team of researchers including Held and led by Pawan Sinha of MIT, published a negative answer to Molyneux’s question. Similar results were reported earlier by a group referred to by Held in “Visual-Haptic Mapping and the Origin of Crossmodal Identity”. The research involved studying youngsters who had been blind from birth, after they had lenses surgically implanted under the auspices of Project Prakash in India. Here is the Abstract of “Visual-Haptic Mapping”:
“We found that the congenitally blind person who gains sight initially fails to identify seen objects with their felt versions: a negative answer to the Molyneux question. However, s(he) succeeds in doing so after a few days of sight. We argue that this rapid learning resembles that of adaptation to rearrangement in which the experimentally produced separations of seen and felt perceptions of objects are rapidly reunited by the process called capture. Moreover, the original ability to identify objects across modalities by the neonate may be assured by the same process.”
—And here is a description of the subjects studied by Ostrovsky et al:
“subjects’ responses were driven by low-level image attributes; [when asked to point to objects] they pointed to regions of different hues and luminances as distinct objects. This approach greatly oversegmented the images and partitioned them into meaningless regions, which would be unstable across different views and uninformative regarding object identity. A robust object representation is difficult to construct on the basis of such fragments” (Ostrovsky, Y., et al. 2009. “Visual parsing after recovery from blindness”. Psychological Science 20, 1484-1491.
In sum, these subjects’ visual experiences were anything but “transparent” to them. The representational content of visual experiences is something we learn to recognize. It is not intrinsic, and a fortiori not identical with their phenomenal character.