Article Information
- Received February 2, 2007
- Revision received June 8, 2007
- Accepted June 11, 2007
- First published August 8, 2007.
- Version of record published August 8, 2007.
Author Information
- 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. matthewb{at}princeton.edu
Author contributions
Disclosures
- Received February 2, 2007.
- Revision received June 8, 2007.
- Accepted June 11, 2007.
-
This work was supported by National Institutes of Health Grant MH16804 (M.B.) and the University of Tokyo International Academic Exchange Grant Program (T.W.).
-
↵a Although our focus in the present work is on activation-based mechanisms for serial order memory centered in the prefrontal cortex, it is important to acknowledge evidence that memory for serial order information may also depend on long-term memory mechanisms housed in medial temporal lobe structures (Fortin et al., 2002).
-
↵b As in the model of Pouget and Sejnowski (1997), no effort was made to capture differences in overall firing rates between cortical regions (e.g., between the IPS and prefrontal cortex). Such an undertaking would face the problem that spike rates in the relevant empirical studies have tended to be reported only in normalized form.
-
↵c Rank units with preferred ranks larger than six were included in the model because, given the graded nature of the rank code, such units naturally contribute to the representation of six-item sequences.
-
↵d Another consequence of this factor is that exchanges between adjacent items become more frequent with increasing rank. Thus, although the format of the data in Figure 3E does not make it evident, the model is less prone to exchange items at positions 2 and 3 than it is to exchange items 4 and 5.
-
↵e The strong recency effect in the figure reflects the fact that early list items are more subject to the cumulative effects of noise. If this factor is equalized across items (as might be justified given that in the laboratory task items are recalled one by one), the straight Gaussian implementation yields a symmetric recall accuracy curve, still inconsistent with the empirical pattern.
- Correspondence should be addressed to Matthew Botvinick, Princeton University, Psychology Department, 3-C-10 Green Hall, Princeton, NJ 08540. matthewb{at}princeton.edu
Online Impact