Path: utzoo!attcan!uunet!lll-winken!ames!ncar!tank!staff_bob@gsbacd.uchicago.edu
From: staff_bob@gsbacd.uchicago.edu
Newsgroups: comp.ai
Subject: Re: Some questions regarding lateral specialization
Message-ID: <1566@tank.uchicago.edu>
Date: 24 Jan 89 01:45:15 GMT
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Organization: University of Chicago Graduate School of Business
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(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?