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From: norman@cogsci.ucsd.EDU (Donald A Norman-UCSD Cog Sci Dept)
Newsgroups: comp.cog-eng
Subject: Re: What is the difference between a metaphor and a mental model?
Keywords: mental models, metaphors
Message-ID: <786@cogsci.ucsd.EDU>
Date: 17 Oct 89 11:46:18 GMT
References: <31966@ucbvax.BERKELEY.EDU>
Reply-To: norman@cogsci.UUCP (Donald A Norman-UCSD Cog Sci Dept)
Organization: UC San Diego Department of Cognitive Science
Lines: 90

..In article <31966@ucbvax.BERKELEY.EDU>
..thom@dewey.soe.berkeley.edu.UUCP (Thom Gillespie) writes: It seems to
..me that you can find metaphors but you can't find mental models. Is
..this my imagination? Please don't tell me that a mental model is a
..bunch of metaphors.

My quick response is:

Mental models and metaphors are very distinct and different things.
But neither are well understood. Lakoff and friends have done much to
popularize the importance of metaphor in thought and language
(also see the earlier book by Ortony -- more in the standard tradition
of psychological and linguistic modeling but also considerably older
and less fun to read).  Metaphors often can serve as starting points
for mental models.

Lakoff, G., & Johnson, M. (1980). Metaphors we live by.  Chicago:
University of Chicago Press.

Ortony, A. (Ed.). (1980).  Metaphor and thought.  Chicago: University
of Chicago Press.
       UCB   Main      BF455 .M47
(UCB library call given since the original correspondent was from UC, Berkeley)

My quick definition -- which won't pass for long but which will help
get things started -- is that a metaphor is the use of knowledge in
one domain as a prototype (model? framework?) for discussing,
understanding or operating in another domain.  This leaves open the
mechanisms and the nature of the mapping between domains, how the
relevant dimensions are appropriated and the irrelevant suppressed or
modified, and how the new domain is appropriately understood despite
the fact that there are known and obvious differences.  There is a
huge amount of work on these aspects of the use of metaphor.

A mental model is the set of mental knowledge (including procedural
knowledge) of the operations of some system.  The model allows for
some level of prediction and understanding, and is of special
relevance when:
	A. initially learning the system;
	B. things go wrong and troubleshooting must take place;
	C. unexpected events occur and problem solving behavior is
		necessary.  

Mental models are probably not much used by skilled operators in
routine operation -- they will get aplied only under conditions B and
C, and for really skilled operators, the standard set of
things-going-wrong or "unexpected" events are probably handled by
skilled routines and do not require mental models or troubleshooting.
Thus, skilled airline pilots are so well trained for most major
malfunctions so that they seldom need to call upon mental models of
the aircraft and its systems.(This is one of those observations not
necessarily accepted by everyone, but that to me explains some of the
limitations of the mental model work and why they have been so
difficult to study).

Metphaors are often useful to describe and explain new systems by
allowing the intial learning to capitalize on prior knowledge.  This
does not mean that metaphors are mental models -- they, by themselves,
do not provide explanatory structure nor proecedural information.  And
metaphors are, well, metaphorical -- they never are completely
appropriate for the new domain.  A mental model does have explanatory
and procedural information and is specifically for the domain in
question.  As Lakoff et al show, metaphors also carry with them a lot
of extra baggage that carries considerable inference power and
entailements that may or may not be what the users intended, but the
metaphor esentially forces them into buying into the entire structure.

--- 

Perhaps you can begin to see that the discussion will expand rapidly
from here.  The long-for-email, but short-for-science discussion above
leaves much to be desired and probably confuses and confounds some
issues.

Personally, I have found the literature on mental models to be less
and less useful -- almost makes me doubt their existence.  They are
tricky things to study, but some progress has been made.  A good
summary is:

Rouse, W. B., & Morris, N. M. (1986). On looking into the black box:
Prospects and limits in the search for mental models. Psychological
Bulletin, 100, 349-363.

----------------------------------------------------------------------

Don Norman                         	       INTERNET:  dnorman@ucsd.edu
Department of Cognitive Science D-015	       BITNET:    dnorman@ucsd
University of California, San Diego	       AppleLink: d.norman
La Jolla, California 92093 USA
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