Paper on MDS available

[Geoffrey Goodhill]

The following paper has been submitted for publication and is
available by anonymous ftp. It expands on our brief preliminary note
published in Nature on June 9th (Simmen, Goodhill & Willshaw, 369:448).


       An evaluation of the use of Multidimensional Scaling 
       ----------------------------------------------------
              for understanding brain connectivity
              ------------------------------------

     Geoffrey J. Goodhill, Martin W. Simmen & David J. Willshaw
                 Centre for Cognitive Science
                   University of Edinburgh

            Research Paper EUCCS / RP-63, June 1994

Abstract
--------

A large amount of data is now available about the pattern of
connections between brain regions. Computational methods are
increasingly relevant for uncovering structure in such datasets. There
has been recent interest in the use of Nonmetric Multidimensional
Scaling (NMDS) for such analysis (Young, 1992, 1993; Scannell & Young,
1993). NMDS produces a spatial representation of the
``dissimilarities'' between a number of entities.  Normally, it is
applied to data matrices containing a large number of levels of
dissimilarity, whereas for connectivity data there is a very small
number. We address the suitability of NMDS for this case. Systematic
numerical studies are presented to evaluate the ability of this method
to reconstruct known geometrical configurations from dissimilarity
data possessing few levels. In this case there is a strong bias for
NMDS to produce annular configurations, whether or not such structure
exists in the original data. Using a connectivity dataset derived from
the primate cortical visual system (Felleman & Van Essen, 1991), we
demonstrate why great caution is needed in interpreting the resulting
configuration.  Application of an independent method that we developed
strongly suggests that the visual system NMDS configuration is
affected by an annular bias.  We question whether an NMDS analysis of
the visual system data supports the two streams view of visual
processing (Young, 1992).


Instructions for obtaining by anonymous ftp:

% ftp archive.cis.ohio-state.edu
Name: anonymous
Password: <your email address>
ftp> binary
ftp> cd pub/neuroprose
ftp> get goodhill.nmds.ps.Z

The paper is approx 1MB and prints on 23 pages.


Geoff Goodhill  

gjg at cns.ed.ac.uk