Published online by Cambridge University Press: 26 September 2008
Preparation of this manuscript was supported in part by grants to the first author from NINCDS (NS 17604) and NICHHD (HD 12701) and by the Mailman Foundation. The authors would like to express their appreciation to P. Blaney for his helpful comments. Address for correspondence: Rebecca E. Eilers, Mailman Center for Child Development, University of Miami, P.O. Box 016820, Miami, Florida 33101.