From: Chuck.Lavazzi@bbs.oit.unc.edu (Chuck Lavazzi)
Newsgroups: alt.fan.holmes
Subject: Another paper: "Holmesian Deduction and Perceptual Closure"
Date: 5 Oct 92 04:27:00 GMT
Distribution: usa
Organization: Extended Bulletin Board Service


	Another Holmes paper written for a local scion society here in
St. Louis.  Hope you find it interesting.
         HOLMESIAN DEDUCTION AND PERCEPTUAL "CLOSURE"
 
                              OR
 
          There's no such thing as a "lucky guess"!
 
                   (c) 1992 By Chuck Lavazzi
 
     It's no news to anyone that the Canon abounds in
examples of the incisive, lightning-like deductions of
Sherlock Holmes.  Like a historical paleontologist assembling
entire creatures from the evidence of bone fragments, Holmes
reconstructs whole life histories from the minutiae of
everyday activity with amazing ease.  In "The Adventure of
the Yellow Face", for example, the Master arrives at some
truly startling (and, as it happens, startlingly true)
conclusions about Grant Munro from a cursory examination of
the latter's pipe.  He decides that Munro is "a muscular man,
left-handed, with an excellent set of teeth, careless in his
habits, and with no need to practise economy."1  Furthermore,
"he must have been disturbed in his mind to leave a pipe
behind him which he evidently values highly."2
     Astonishing, Holmes!  Commonplace, Watson.  And yet upon
closer examination some of his deductions begin to look more
like guesses -- and lucky ones at that.  Returning to Munro's
pipe, it may be logical to assume that the charring on the
right side of the bowl indicates a left-handed man carelessly
lighting the pipe at a gas-jet, but does biting through the
amber necessarily require "a muscular energetic fellow, and
one with a good set of teeth"?3  Might not a nervous or angry
man with a new set of phony choppers do as well?  Holmes also
concludes that Munro has no need to practise economy because
he smokes "Grosvenor mixture at eightpence an ounce" even
though "he might get an excellent smoke for half the price".4
Yet isn't it also possible that he is so thoroughly addicted
to this particular mixture that he has chosen to economise
elsewhere?  Why choose one alternative and not the other?
     The skeptical reader might conclude that Holmes did the
mental equivalent of a coin toss and simply "got lucky".  The
truly cynical reader might take this one step farther and
conclude that Holmes simply threw out as many deductions as
he could come up with, knowing that some of them would
probably be correct and that the rest would either be
forgotten or edited out by the diplomatic Watson.  This
tactic has, after all, worked pretty well for the Jean Dixons
and Criswells of the world for some time.  And yet I submit
that the real answer is to be found in neither the betting
parlour nor the supermarket tabloid, but rather in the
precepts of Gestalt psychology.
     Let us pause, at this point, for a thumbnail sketch of
this highly significant school of perceptual psychology.  The
Gestalt school was founded in the early years of this century
	by Max Werthiemer (1880 - 1943), Wolfgang Kohler (1887 -
1967), and Kurt Koffka (1886 - 1941), largely as a reaction
to the earlier "reductionist" theories of human perception.
The Gestalt psychologists held that in human perception, the
whole is more than the some of the parts; that our
experiences are the result of more than just the physical
sensations that produce them.  Thus the term "gestalt", which
is German for "form, shape, or figure".
     Of the many principles of Gestalt psychology, the one
most relevant here is the concept of "closure".  This is the
tendency of the perceiver to "fill in the gaps" in an object
or situation; to "give the best definition, symmetry and form
to perceptual figures." (Chaplin and Krawiec, 1968).5  The
figure below, for example, is perceived as a bird, even
though it is only a collection of disconnected ASCII
characters:
                     _ 
                   ( v )
                   () ()
                    ^ ^
 [Note: it looked more like one in the original paper, where
I was able to include high ASCII characters..]

And this is seen as a rectangle, even though it is really
four disconnected lines:
                   -----------
                   |         |
                   |         |
                   |         |
                   |         |
                   |         |
                   -----------
     In short, the Gestalt psychologists maintained that the
human mind routinely assembles disjoint physical events into
perceptual "wholes" or Gestalten.  In the same way  Holmes
was able to assemble a whole picture of a person or event
from apparently disconnected items or occurrences.  His
choices among (apparently) equally likely alternative
explanations are not so much "lucky guesses" as rational
assessments of conditional probabilities that allow him to
achieve "closure" and arrive at a coherent picture of the
whole.
     Thus, to return to our original example from "The Yellow
Face",6 the alternative explanations for the bitten-through
amber and the pricey tobacco may be acceptable possibilities,
but they are unacceptable probabilities in light of the
other, more certain data.  Holmes merely achieved cognitive
closure the same way the rest of us poor mortals achieve
visual closure every day.  That he did so on such a regular
basis is, in my humble opinion, largely a tribute to his
ability to quickly analyze and evaluate data in a manner
unequalled until the advent of the modern computer.  Small
wonder that he was regarded as a kind of "thinking machine"
by his contemporaries!
 
 
 
 
 
Footnotes:
1 Yellow Face, p. 352
2 Ibid
3 Ibid
4 Ibid
5 Chaplin, J.P and Krawiec, T.S.  Systems and Theories of
 Psychology  New York; Holt, Rinehart and Winston, 1968
6 Bet you'd thought I'd forgotten it, didn't you?

Chuck
No .sig, no frills, no foolin'

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