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Falling towards Forgetfulness: Synaptic Decay Prevents Spontaneous Recovery of Memory

Stone, J.V., Jupp, P.E. and Friston, K.J. (2008) Falling towards Forgetfulness: Synaptic Decay Prevents Spontaneous Recovery of Memory. PLoS Computational Biology, 4 (8). e1000143. ISSN 1553-7358

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Long after a new language has been learned and forgotten, relearning a few words seems to trigger the recall of other words. This “free-lunch learning” (FLL) effect has been demonstrated both in humans and in neural network models. Specifically, previous work proved that linear networks that learn a set of associations, then partially forget them all, and finally relearn some of the associations, show improved performance on the remaining (i.e., nonrelearned) associations. Here, we prove that relearning forgotten associations decreases performance on nonrelearned associations; an effect we call negative free-lunch learning. The difference between free-lunch learning and the negative free-lunch learning presented here is due to the particular method used to induce forgetting. Specifically, if forgetting is induced by isotropic drifting of weight vectors (i.e., by adding isotropic noise), then free-lunch learning is observed. However, as proved here, if forgetting is induced by weight values that simply decay or fall towards zero, then negative free-lunch learning is observed. From a biological perspective, and assuming that nervous systems are analogous to the networks used here, this suggests that evolution may have selected physiological mechanisms that involve forgetting using a form of synaptic drift rather than synaptic decay, because synaptic drift, but not synaptic decay, yields free-lunch learning.

Item Type: Article
Copyright, Publisher and Additional Information: © 2008 Stone,Jupp. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Department of Psychology (Sheffield)
Depositing User: Sheffield Import
Date Deposited: 30 Oct 2009 13:36
Last Modified: 09 Jun 2014 11:36
Published Version: http://dx.doi.org/10.1371/journal.pcbi.1000143
Status: Published
Publisher: Public Library of Science
Identification Number: 10.1371/journal.pcbi.1000143
URI: http://eprints.whiterose.ac.uk/id/eprint/10030

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