Thursday, March 5, 2015
Response to a Comment by Ned Block
Ned Block writes:
“I think what Sinha showed is that there is a critical period for object-perception. [Ned is referring to my post “Perceptual Transparency and Sinha’s Observations” 1/20/15] He did not show that we have to learn cross-modal connections. There is a ton of data showing that human-babies have built-in cross modal connections at birth. Human babies will turn toward a sound at birth. And human babies prefer to look at a picture of the pacifier they have in their mouth. Also babies imitate facial expressions.” [you can find a video by searching under “Neonate Imitation”]
Ned is absolutely right. I did not know about the critical period. Here is some material on that from the National Institutes of Health:
“This idea of a developmental critical period is largely based on animal studies performed during the 1960s. It’s an influential idea which many researchers use as a basis to design and interpret experiments and many doctors use to make treatment decisions.
Nonetheless, there have been a few rare cases of blind patients who gained sight later in life and learned to recognize some objects. Furthermore, children born blind with cataracts but who had gained sight from surgery a few months after birth eventually learned to recognize most objects. These cases suggest that our brains may be able to learn to see regardless of whether we have vision problems during the critical period.
Every child Project Prakash treats provides one more reason to think that the brain is more flexible than we once thought. So far, the project has treated 200 children, many of whom are older than six years of age. Nine of "the children have been described in scientific journal articles. The average age of these children was 13 years old, ranging from 7 to 24.
Although they do not have perfect vision, all of them have learned to recognize most objects and can rely on their vision to work and play like people who grew up with normal vision. These results support the idea that our brains can learn to recognize objects after the critical period.”
How does this information affect the case I have been making in these posts? That case is directed against the idea that visual experiences are intrinsically transparent, as Tye has claimed. But the Sinha-Held observations as well as Held’s experiments with kittens in the 1960s show that, regardless of whether it be because visual-haptic connections have to be learned (as I thought) or because they have to be activated during a critical period, as is now believed, they are not universally present – not in the case in which that activation fails to occur. Nor is it the case that in the first hours after sight is restored, the visual objects are experienced as of “external” objects. To quote again [see my post “More on Transparency” 2/2/15] from the description given by Ostrovsky et al (who examined the children in India immediately afer they received the corneal implants)—
“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”.
The visual experiences of those children at those times weren’t “transparent” to them. Afortiori, transparency is not an intrinsic property of visual experiences. I added that the visual-haptic connections are “quickly learned”, and I would now say, “quickly activated”, but my point is unaffected: “transparency” is not an intrinsic feature of visual experience.