models versus data

[Tony Marley]

FROM: Tony Marley, Director, McGill Cognitive Science Centre.
RE: Models versus Data.
 
    In the light of recent discussions of modeling versus data, I
thought it might be worthwhile (re)drawing attention to the following
paper by Yellott. One of the recent examples discussed was the
Hartline-Ratliff model of the limulus eye, and Mach bands, using
a LINEAR SYSTEM WITH INHIBITION - one argument being that this was
excellent work as the model was driven by biological data. The
interesting aspect of Yellott's work is that he obtains Mach bands
from a NONLINEAR SYSTEM WITHOUT INHIBITION, and argues that it is
difficult on the basis of current physiological data to decide which
model is "correct". (I do not believe that he specifically discusses the
limulus eye so perhaps the data is clear there).
    Anyway, the point is to reiterate how theory dependent
interpretation of (raw) data can be.
 
ARTICLE:
 
YELLOTT, J. I. (1989). Constant volume operators and lateral inhibition.
Journal of Mathematical Psychology, 33, 1-35.
 
    "Constant volume (CV) operators are nonlinear image processing
operators in which the area covered by the pointspread function around
each point in the input image varies inversely with light intensity at
that point. This operation is designed to make spatial resolution
increase with retinal illumination, but it proves to have unexpected
side-effects that mimic other important properties of human spatial
vision, including Mach bands and Weber's law. Mach bands are usually
attrtibuted to lateral inhibition in the retina, and when retinal image
processing is modeled by a linear operator they imply such inhibition,
since they cannot be produced by a nonnegative impulse response. CV
operators demonstrate that Mach bands and other high-pass filter effects
can be created by purely positive pointspread functions, i. e. without
inhibition. This paper shows in addition that if one attempts to combine
lateral inhibition with a CV operator, the results are dramatically
wrong: the edge response always contains Mach bands that bulge in the
wrong direction. Thus within the nonlinear theoretical framework
provided by CV operators, lateral inhibition is neither necessary or
sufficient for modeling Mach bands and other high-pass filter properties
of spatial vision."
 
 
(Yellott is at the Cognitive Sciences Department, University of
California, Irvine, CA 92717.)