The Journal of Neuroscience, August 8, 2007, 27(32):8636-8642; doi:10.1523/JNEUROSCI.2110-07.2007
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Behavioral/Systems/Cognitive
From Numerosity to Ordinal Rank: A Gain-Field Model of Serial Order Representation in Cortical Working Memory
Matthew Botvinick1 and
Takamitsu Watanabe2
1Psychology Department and Institute for Neuroscience, Princeton University, Princeton, New Jersey, 08540, and 2Department of Physiology, University of Tokyo School of Medicine, Tokyo 113-0033, Japan
Correspondence should be addressed to Matthew Botvinick, Princeton University, Psychology Department, 3-C-10 Green Hall, Princeton, NJ 08540. Email: matthewb{at}princeton.edu
Encoding the serial order of events is an essential function of working memory, but one whose neural basis is not yet well understood. In the present work, we advance a new model of how serial order is represented in working memory. Our approach is predicated on three key findings from neurophysiological research: (1) prefrontal neurons that code conjunctively for item and order, (2) parietal neurons that represent count information through a graded and compressive code, and (3) multiplicative gain modulation as a mechanism for information integration. We used an artificial neural network, integrating across these three findings, to simulate human immediate serial recall performance. The model reproduced a core set of benchmark empirical findings, including primacy and recency effects, transposition gradients, effects of interitem similarity, and developmental effects. The model moves beyond previous accounts by bridging between neuroscientific findings and detailed behavioral data, and gives rise to several testable predictions.
Key words: prefrontal cortex; parietal cortex; working memory; serial order; computational models; numerosity
Received Feb. 2, 2007;
revised June 8, 2007;
accepted June 11, 2007.
Correspondence should be addressed to Matthew Botvinick, Princeton University, Psychology Department, 3-C-10 Green Hall, Princeton, NJ 08540. Email: matthewb{at}princeton.edu