Technical Report available

[Peter Foldiak]

The following report is now available:

                  Models of sensory coding
                       Peter Foldiak
    Cambridge University Engineering Department Tech. Report
                   CUED/F-INFENG/TR 91
      (technical report version of Ph.D. dissertation)

For a copy, send physical mail address to:
  peter at psy.oxford.ac.uk
or to
  Peter Foldiak
  MRC Research Centre in Brain and Behaviour,
  Dept. Experimental Psychol., University of Oxford,
  South Parks Road, Oxford OX1 3UD, U.K.

(I may also have to ask you for a check to cover postage.)
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Abstract

1 - An 'anti-Hebbian' synaptic modification rule is demonstrated
to be able to adaptively form an uncorrelated representation of
the correlated input signal. This mechanism can match the
distribution of input patterns to the actual signalling space
of the representation units, achieving information-theoretically
optimal signal on noisy units. An uncorrelated, equal variance
signal also makes fast, optimally efficient least-mean-square (LMS)
error correcting learning possible.

2 - A combination of Hebbian and anti-Hebbian connections is
demonstrated to implement a form of the statistical method of
Principal Component Analysis, which reduces the dimensionality
of a noisy Gaussian signal while maximising the information
content of the representation, even when the units themselves
are noisy.

3 - A similar arrangement of biologically more plausible, non-
linear units is shown to be able to adaptively code inputs into
a sparse representation, substantially reducing the higher-
order statistical redundancy of the representation without
considerable loss of information. Such a representation is
advantageous if it is to be used in further associative learning
stages.

4 - A Hebbian rule modified by a trace mechanism is studied, that
allows processing units to respond in a way which is invariant
with respect to commonly occurring transformations of the input
signal.

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