N. Brunel, EFFECT OF SYNAPSE DILUTION ON THE MEMORY RETRIEVAL IN STRUCTURED ATTRACTOR NEURAL NETWORKS, Journal de physique. I, 3(8), 1993, pp. 1693-1715
We investigate a simple model of structured attractor neural network (
ANN). In this network a module codes for the category of the stored in
formation, while another group of neurons codes for the remaining info
rmation. The probability distribution of stabilities of the patterns a
nd the prototypes of the categories are calculated, for two different
synaptic structures. The stability of the prototypes is shown to incre
ase when the fraction of neurons coding for the category goes down. Th
en the effect of synapse destruction on the retrieval is studied in tw
o opposite situations : first analytically in sparsely connected netwo
rks, then numerically in completely connected ones. In both cases the
behaviour of the structured network and that of the usual homogeneous
networks are compared. When lesions increase, two transitions are show
n to appear in the behaviour of the structured network when one of the
patterns is presented to the network. After the first transition the
network recognizes the category of the pattern but not the individual
pattern. After the second transition the network recognizes nothing. T
hese effects are similar to syndromes caused by lesions in the central
visual system, namely prosopagnosia and agnosia. In both types of net
works (structured or homogeneous) the stability of the prototype is gr
eater than the stability of individual patterns, however the first tra
nsition, for completely connected networks, occurs only when the netwo
rk is structured.