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perceptual variables and data variables

Al Bregman says
> A dimension of
> experience, such as pitch, can be either prothetic or metathetic
> (metathetic, in the case of pitch).  The mass of an animal is physical, so
> it can't be either prothetic or metathetic.
> It occurred to me that if we're not allowed to link quantitative physical
> variables such as wavelength or repetition rate with metathetic variables
> of experience, such as color or pitch, psychophysics (i.e., Psycho <--
> physics) becomes impossible.

in visualization Bertin has
proposed a formal method for representing
data variables with perceptual variables

the idea is that a prothetic variable
such as colour lightness or sound loudness
which has a true or "natural" zero and a unidimensional metric
(i.e. colour can't be seen when lightness goes to zero,
sound can't be heard when loudness goes to zero)
allows faster, more accurate perceptions of ratio data
(i.e. data with a true zero and a unidimensional metric
such as the mass of an animal)

metathetic variables such as colour hue,
allow the better perception of difference without order
in judgements of difference between categorical data
(for example different colours for different species of
animals in a graph)

pitch has order and difference, but no zero
so allows better perception of ordinal data
(for example ordered categories such as
the likelihood of rain classed as "low, medium or high")

further reading if interested ...

Bertin J. (1981) Graphics and Graphic Information Processing, Walter de

Casner S. (1992) A Task Analytic Approach to the Automated Design of
Graphic Presentations, ACM Transactions on Graphics, 10, pp 111-151.

Cleveland W.S. (1985) The Elements of Graphing Data, Wadsworth Advanced
Books and Software, Monterey, California.

Norman D.A. (1991) Cognitive Artifacts, in Carroll J.M. (ed), Designing
Interaction : Psychology at the Human-Computer Interface, Cambridge
University Press.

Rogowitz B.E. and Treinish L.A. (1993a) Data Structures and Perceptual
Structures,  Proceedings of the SPIE Human Vision, Visual Processing and
Digital Display IV, SPIE Vol. 1913.

Ware C. (1993) The Foundations of Experimental Semiotics: a Theory of
Sensory and  Conventional Representation, Journal of Visual Languages
and Computing, 4, pp 91-100, Academic Press Limited, London.

Grüßen stephen

  Stephen Barrass Ph.D. <http://viswiz.gmd.de/~barrass/thesis/>
  Virtual Environments  <http://viswiz.gmd.de>
  GMD IMK, Schloss Birlinghoven, D-53754 St. Augustin, Germany
  fax:+49-2241-14-2040 phone:+49-2241-14-2838(w) +49-0228-465432(h)

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