I am teaching "Human Nature and Human Values" again and that always means consuming a lot of recent research. One study I just digested into PowerPoint slides concerned the development of language by infants. Back when I was (briefly) a psychology major (late 1970's), I was taught that language is acquired by mere power of association. When an infant is exposed to one auditory stimulus (a word) in frequent conjunction with another (an object), then the infant learns that word for that object. That is the Standard Social Science Model. All social behavior is explained by reference to other social behavior.
For that model to be confirmed, it should be the case that any sufficiently recognizable auditory stimulus would do. For example, a buzz or buzz and click should be learned as a word for nose, if that is what the infant is taught.
A recent study indicates that only certain kinds of auditory stimuli trigger the learning of words and that these stimuli in conjunction with visual examples triggers categorization in infants as young as three months old. I find that very exciting.
The study is "Nonhuman primate vocalizations support categorization in very young human infants" by Alissa L. Ferry, Susan J. Hespos, and Sandra R. Waxman (PNAS | September 17, 2013 | vol. 110 | no. 38 | 15231–15235). Ferry et. al. exposed infants to images of dinosaurs in conjunction with a range of auditory signals, including tones and backward human speech. Then they showed the subject two images, one of which was a new dinosaur and the other a fish. They measured learning by whether the infant gazed at the dinosaur rather than the extra-categorical image.
It turns out that tones and backward speech had no effect. The infants did not associate these auditory stimuli with categories of objects. Nor did they respond to the visual stimuli alone, in the absence of any auditory stimulus. However, when the infants were exposed to coherent human speech or nonhuman primate vocalizations along with the images in the first stage of the test, then they recognized the novel dinosaur in the second stage of the test.
That the infants responded to human vocalization in the first stage but not to tones or backward speech suggests that they are primed to tune in to certain stimuli but not others. This indicates an evolved psychological mechanism for learning language. That they recognized a new member of a previously presented category after only a very brief exposure indicates that this mechanism, far from being a mere power of association, includes a power of forming mental categories. At three months of age. That their power of categorization was triggered both by human speech and nonhuman vocalization indicates that this mechanism has deep evolutionary roots, going back well before the emergence of human beings on this planet.
The Socratic philosophers were onto this more than two thousand years ago. Plato knew that human beings could form altogether artificial categories, such as "all numbers except 17". That capacity exists, however, because it reflects and exemplifies something essential about the world we live in. The world sorts itself into categories: rocks and living creatures, plants and animals, dinosaurs and mammals, horses and cows.
Evolutionary theory wonderfully enriches the Socratic idea. The ability to recognize categories of things is not only a consequence of evolution is part of the dynamic of evolution. One theory of what a biological species is turns precisely on species recognition. Horses are horses and not cows because they recognize horses as potential mates. That horses can breed with donkeys indicates that the two species have split but remain just close enough to produce mules.
The Greek word logos was pregnant with meaning. It meant first the human power of speech. It was extended to include human reason and the truths that reason could reveal. Later, it came to mean the coherence of the intelligible kosmos. Philology recapitulates metaphysics, in Greek philosophy and evolutionary psychology. In the beginning was the word.
I found this analysis fascinating, however I am having a little trouble agreeing with all of it.
ReplyDeleteYou write:
"Horses are horses and not hows because they recognize horses as potential mates." If this is the case, why aren't dogs legs?
Since horses have - upon occasion - tried to mate with other animals (and other animals have tried to mate with horses) can we be sure recognition of potential mates plays a strong role in the solidification of the horse's horse-ness?
Miranda: you put your finger squarely on a fundamental problem that haunts biology. There doesn't seem to be any theory of species that works in all cases.
ReplyDeleteI am tempted to reply that no leg every tried to mate with a dog and thus require mutual recognition; however, the species recognition formula probably works only in conjunction with Ernst Mayr's interbreeding idea. To offer a simple formulation: two individuals belong to the same species if they can have grandchildren.
It doesn't tell against this definition that some persons are sterile. Just because some people are blind doesn't change the fact that the function of eyes is sight. That animals occasionally try to mate outside their species only shows us that the power of recognition can fail. As Aristotle noted, we understand something natural when we can distinguish between the healthy and the unhealthy examples.
The bigger problem is that this definition is that it only works for sexually reproducing organisms. What about single celled bacteria?
I am inclined to see each species as an object, extended in space. So deer are like triangles and ungulates are like plane figures. In one sense a deer and an elk are one species; in another, not.
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ReplyDeleteDr. Blanchard: I like the idea of triangular deer!
ReplyDeleteEverything you've written here makes a good deal of sense to me - but I think there may be a difference between blindness - which is relatively rare - and dogs trying to mate with objects and animals they cannot successfully mate with - which is very common.
I think, perhaps, you are giving animals too much credit - and that the reason dogs are dogs and horses are horses is not that they can recognize other animals in their species as mates, but because it is impossible for them to reproduce with the other objects they may try to mate with.
But I agree with you that the case of single-celled bacteria presents a bigger problem.
Tempted as I am to pretend that I understand how deer are like triangles and ungulates are like planes, math has never been my strong suit.
I THINK what you are saying is that just as a plane can be a square or a triangle, an ungulate can be a deer or an elk, so in one sense, deer and elk belong to the same category - but just as triangles are specific planes and squares are not triangles - deer are very specific ungulates and not the same as elk. But what does this tell us about single-celled bacteria?
Miranda: Human beings masturbate. That doesn't mean that they are trying to mate with themselves. The psychological/physical mechanisms that are part of the mating array occasionally engage out of context or serve other functions. Consider Bonobos, who use sexual stimulation to resolve conflicts between males or to cement female alliances. If a dog humps a leg, that is because it feels good. I wouldn't infer that the dog can't tell the difference between a leg and another dog.
ReplyDeleteI am no math whiz either, but I know the difference between a triangle and a square. I also know the difference between a dog and a cat.
If we can't make the same distinctions between bacteria, that means that these creatures haven't achieved the same categorical being that we have. Hence my point.
Thanks, Dr. Blanchard. This makes sense. I appreciate you taking the time to answer.
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