Joe Joseph_Pullara at Maillink.berkeley.edu
Wed Jul 27 14:02:04 EST 1994

In article <3163m6$a27 at news.cc.oberlin.edu>
ssl7091 at ocvaxa.cc.oberlin.edu (We have met the enemy, and they are
illiterate.) writes:

> idea of the two hemispheres of a dolphin's brain being alternately
> active also presents a satisfying answer to the puzzle that dolphins'
> cerebral quotient (or something like that-- brain weight to body weight
> ratio , or something similar) is similar to humans', about twice that
> of chimps and apes and far above anything else.  Under this theory,
> dolphins' quotient can be effectively chopped in half, making it the
> same as a chimp's, 


Using this logic, "split-brain" humans (those whose corpus callosum has
been surgically severed) are only half as intelligent after the
surgery.  Not true. In fact it takes fairly sophisticated
neuropsychological testing to reveal the changes which occur after
disconnecting the hemispheres.

Look at it this way, a certain amount of brain tissue is required to
process, evaluate and act on sensory input. The more tissue, the more
sophisticated the evaluation, processing and output. Each hemisphere is
responsible for sensory and motor function for one half of the body
_whether_they're_connected_or_not. In dolphins, the corpus collosum may
have fewer fibers than humans but that only means that there is less
need for communication between hemispheres. I don't know why this would
be, though perhaps it has something to do with the fact that the
sensory modalities upon which dolphins rely most, echolocation and
audition, are less lateralized than vision (upon which we rely the
most). Certainly it has no bearing on their intelligence.

>which makes a lot more sense given what we know about
> what dolphins, chimps, and people can learn.

Actually we know very little about what dolpnins _can_ learn since we
occupy  a very different sensory space (visual and low frequency
audition vs echolocation and high frequency audition).  For example a
rat might conclude that we are very stupid since we cannot learn in
their primary sensory space (olfaction). Can you smell your way home?

- Joe Pullara
  UC Berkeley

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