staff_bob@gsbacd.uchicago.edu (01/24/89)
(Diana Smetters) writes... > >I have a question about arguments which mention that hemispheric >specialization is present "from the start" or "very early in life" >and then go on to use the presence of this specialization to deduce that >such specialization is innate. Namely: how early is "very early" -- if >you consider the fact that evidence that a particular pattern of hemispheric >specialization is present in the 2yr old child, or even the 3 month >old infant does not constitute evidence that such specialization is >genetically predetermined. A 3 month old infant has already been subject >to a large number of "environmental" influences -- both at the level >of the uterine environment and at the cellular level, in terms of the >chemical influences on the migrating neurons. > This is a very good question, and while no one yet knows to what extent the hemispheres differ at birth, there has been a good deal of research which show that they do differ. In one of the articles I mentioned in my last posting, Molfese (1977) "Infant Cerebral Asymmetry" in Segelowitz and Gruber(eds.) "Language Development and Neurological Theory", the author discusses an experiment performed on infants less than 24 hours old. Among other things, he found that the left hemisphere in more responsive to certain forms of speech stimuli than the right. For other evidence, see Witelson and Pauli (1973). "Left hemisphere specialization for language in the newborn: Neuroanatomical evidence of asymmetry." Annals of the New York Academy of Sciences, 299. 328-354 or Wada, Clark and Hamm (1975) "Cerebral asymmetry in humans: Cortical speech zones in 100 adults and 100 infant brains", Archives of Neurology. 32. 29-38 If studies on infants aren't enough, I even found one reference which purports to have demonstated differences after 31 weeks of gestation: Chi, Dooling and Gilles (1977) "Left-right asymmetries of the temporal speech areas of the human fetus." Archives of Neurology, 34. 346-348 >In addition, I wish to mention that the fact that all individuals seem >to undergo some pattern of hemispheric specialization does not mean that >all individuals undergo the *same* pattern of hemispheric specialization. >(See Geschwind and Galaburda: "Cerebral Dominance" and "Cerebral >Lateralization"). > This is quite correct, and ever worth bearing in mind. The left vs. right brain distinction is problematical in that a) there is a wide variance of the degree of lateralization across individuals and b) both hemispheres appear to be at least somewhat capable of performing the sort of task best performed by its opposite. >Lastly, and most emphatically: the evidence to date concerning cerebral >lateralization has focused primarily around lesion studies. There is >evidence of such things as: lesions to areas of the left hemisphere >(ex. Broca's area) tend to produce certain types of language dysfunction. >From this, one can deduce things like "many aspects of language function >may be carried out by the left hemisphere (in most people)". This >does not give any evidence for the claims that the left hemisphere >is logical/analytical, while the right is concerned with creativity, >art, etc. If anyone could give me references that show this sort of >lateralization of higher cognitive functions like "logical thought", >"creativity", "aesthetics", etc., I would really appreciate it. The >fact that the left hemisphere may handle the bulk of low-level language >processing, and that the right may handle spatial processing and the >generation of mental images (to be kept strictly distinct from the >process known as imagination), does not seem (to me, at least) to constitute >evidence for the lateral specialization of any of the high-level >cognitive processes which have been discussed here (under the denotation >"mysticism"). > To begin with, I have never claimed that there is any evidence that the right brain is somehow more "mystical" than the right. I do however believe that the possibility is worth investigating, in the sense that if the two halves of the brain are in fact different, whether or not the difference is innate, then one would expect that one hemisphere would have problems "understanding" the other. Then "Mysticism" reduces to the inability of the left hemisphere to understand the right in its own terms. As for evidence, the suggestion that the evidence for cerebral asymmetry is primarily based on lesion studies may have been true during the days of Broca and Wernicke, but today it seems to be stretching things. There is a good deal of research on normal humans, as well as the well known studies of split brain behavior. A good introductory book on the subject is (was) Gazzaniga and LeDoux(1978), "The Integrated Mind", Plenum Press. How well this concurs with present research, I cannot say as I have been out of the field for some time. I cannot imagine that things are now less well defined than they were then. However, I must confess that with certain exceptions, I know of no research linking "high-level" function to one side of the brain or the other. This may simply be a result of my ignorance, or it may be a result of the difficulty of such research. To my thinking, this does not mean we should adopt the attitude that "this has not been proven, so I refuse to accept it." We do have evidence that the right hemisphere (in right handed individuals) is more spatially sophisticated, holistically oriented, musically inclined and better at recognizing visual images than the left. The left, (literally) on the other hand, is more symbolic and analytical. If you want me to find references to support this, please let me know, but I believe this much is generally accepted. These are generally what I would consider "low-level" skills, and to some extent I am sure that we have been able to place them in one hemisphere or the other because they are easier to measure than more complex abilities, which may involve both hemispheres simultaneously. The reason I believe lateral asymmetry is worth keeping in mind may best be demonstrated with the following anecdote. In "The Integrated Mind", there is a description of a split-brain patient who was asked "What job would you like to have?" His left hemisphere, which had presumably been his dominant hemisphere, answered that it would like to be a draftsman. The right hemisphere declared that it wanted to race cars. It is quite reasonable to assume that this same duality of preference existed before the corpus callosum was cut, and one can imagine that the response frm the unified brrain would have been "draftsman." It occured to me that the same sort of conflict seems to be present in the debate which I had been observing here between what I will loosely call the "rationalists" and the "mystics". No one seems to argue with the former term; I'm not particularly happy with the latter, but I'm at a loss for a better one. Is it not possible that this debate, which I daresay is considerably older than this newsgroup, is the product of a fundamental dichotemy of our own minds?
bwk@mbunix.mitre.org (Barry W. Kort) (01/29/89)
In article <1566@tank.uchicago.edu> staff_bob@gsbacd.uchicago.edu writes: > I have never claimed that there is any evidence that the > right brain is somehow more "mystical" than the right. I do however > believe that the possibility is worth investigating, in the sense that > if the two halves of the brain are in fact different, whether or not > the difference is innate, then one would expect that one hemisphere > would have problems "understanding" the other. Then "Mysticism" reduces > to the inability of the left hemisphere to understand the right in its > own terms. > We do have evidence that the right hemisphere (in right handed individuals) > is more spatially sophisticated, holistically oriented, musically > inclined and better at recognizing visual images than the left. The left, > (literally) on the other hand, is more symbolic and analytical. In my experience, it is damn hard to devise a translation between left and right hemispheric representations of the same information. It was not obvious to me that conic sections were representable as quadratic equations. And all of analytical geometry turned out to be a great boon. Still, when I catch a frisbee, I do not calculate trajectories with my left hemisphere. But please don't ask me how I catch the frisbee. My right hemisphere refuses to divulge its methods. Similarly, I labor to translate time domain signals into the frequency domain with Fourier transforms. But somehow my right hemisphere effortlessly recognizes notes and tunes from time-domain playbacks of my records and tapes. And I cannot look at the grooves on the record and recognize the music (although some people have reportedly learned to do so). Worse yet, I can't read music. Show me the sheet music to a common tune and I just shrug my shoulders. My television paints a picture by raster scanning, much like the way I read pages in a book. But my visual system just sees the TV image "all at once," and I'll be damned if I can tell you how that works. I certainly couldn't teach scene recgonition to anyone (and especially not to a computer). So I agree that the left hand doesn't know what the right hand is doing (most of the time), and even if it does, it doesn't know how the other half figures it out. One thing I do know. For those few cases where I can readily translate back and forth between left and right hemispheric representation of the same information, I can make a comfortable living. --Barry Kort