1Laboratory of Neurosciences, National Institute on Aging, Bethesda, MD, USA
3Laboratory of Brain and Cognition, National Institute of Mental Health, Bethesda, MD
4Institute for Cognitive and Computational Sciences, Georgetown University, Washington, DC, USA
2Present Address: Rotman Research Institute, Baycrest Centre for Geriatric Care, 3560 Bathurst St., Toronto, Ontario M6A 2E1, Canada
5Corresponding Author and Address: Cheryl L. Grady, Rotman Research Institute, Baycrest Centre for Geriatric Care, 3560 Bathurst St., Toronto, Ontario M6A 2E1, Canada
ACKNOWLEDGEMENTS: The authors wish to thank Dr Francois Lalonde, David Mangot, Richard Desmond, and Eileen Daly for their technical help in carrying out this experiment. We also wish to thank Dr Claude Alain for his helpful comments on the manuscript.
Received 8 April 1997; accepted 21 May 1997
