[1] MRC, Cognit & Brain Sci Unit, Cambridge, England
[2] Univ Cambridge, Cambridge Ctr Ageing & Neurosci, Cambridge, England
[3] MRC Cognit & Brain Sci Unit, Cambridge, England
[4] Harvard Univ, Dept Psychol, Cambridge, MA 02138 USA
[5] Duke Univ, Dept Psychol & Neurosci, Durham, NC 27706 USA
[6] Univ Manchester, Sch Biol Sci, Manchester M13 9PL, Lancs, England