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Proceedings Paper

Implementation of the Hopfield model with excitatory and inhibitory synapses and static thresholding
Author(s): Amanda J. Breese; John Macdonald
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Paper Abstract

Optical implementations of neural networks based on the Hopfield model have always found it difficult to produce the negative weights required for the interconnecting synaptic matrix. One solution involves the addition of a positive offset to the weights to ensure that they all become non-negative but this introduces another problem as a dynamic (or time-dependent) threshold value is then required which may be difficult to implement. The dynamic threshold arises out of an inconsistency in the implementation. To overcome this our implementation employs a biased (non-negative) interconnection matrix which is dynamically multiplied by a diagonal matrix version of the neural state vector so that the same biasing is experienced. The above problem then no longer arises and we are left with a static threshold value. The method is demonstrated in an optoelectronic system employing 50 fully interconnected neurons. This uses a laser source for the neurons a computer driven liquid crystal spatial light modulator to produce the interconnection weights and a photodiode array with appropriate electronic circuitry to introduced the summing and thresholding aspect. 1. .

Paper Details

Date Published: 1 August 1990
PDF: 7 pages
Proc. SPIE 1294, Applications of Artificial Neural Networks, (1 August 1990); doi: 10.1117/12.21191
Show Author Affiliations
Amanda J. Breese, Univ. of Reading (United Kingdom)
John Macdonald, Univ. of Reading (United Kingdom)


Published in SPIE Proceedings Vol. 1294:
Applications of Artificial Neural Networks
Steven K. Rogers, Editor(s)

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