The worldwide demographic explosion in numbers of older people makes the study of cognitive change in old age of obvious practical interest. It is also theoretically crucial because it demands models for cognitive change that can explain how some cognitive skills are retained while others are lost and how tasks that we once performed superbly well are compromised by biological changes in the brain.
A striking weakness of models in contemporary Experimental Cognitive Psychology is that they only describe functional systems that cannot occur in nature because they do not alter with practice, or during childhood development and age-related decline, and are identical in all individuals. Cognitive Gerontologists are deprived of such convenient fictions because their hope is to explain how we gradually become less competent at things that we once did extraordinarily well. They encounter the quite different, and salutary, difficulty that calendar time, the dimension in terms of which old and young people are conventionally differentiated, only indicates the maximum period within which an enormous range of disparate changes can have occurred. These changes certainly include poorly-understood processes of "normal" or "usual" ageing but also the cumulative effects of the pathologies and biological life events that, to varying degrees, affect our brains.
The papers in this special issue, all by leading researchers, highlight the important practical and theoretical advances in the understanding of the impact of these changes in the ageing brain on the ageing of our cognition.
P.M.A. Rabbitt, Introduction. K.J. Anstey, K. Dear, H. Christensen, A.F. Jorm, Biomarkers, Health, Lifestyle and Demographic Variables as Correlates of Reaction Time Performance in Early, Middle and Late Adulthood. S.L. McCoy, P.A. Tun, L.C. Cox, M. Colangelo, R.A. Stewart, A. Wingfield, Hearing Loss and Perceptual Effort: Downstream Effects on Older Adults' Memory for Speech. H.J. Haarmann, G.E. Ashling, E.J. Davelaar, M. Usher, Age-related Declines in Context Maintenance and Semantic Short-term Memory. P.G. Rendell, A.D. Castel, F.I.M. Craik, Memory for Proper Names in Old Age: A Disproportionate Impairment? W.L. Whiting, D.J. Madden, T.W. Pierce, P.A. Allen, Searching from the Top Down: Aging and Attentional Guidance During Singleton Detection. G. Ward, E.A. Maylor, Age-related Deficits in Free Recall: The Role of Rehearsal. S. Kim, L. Hasher, The Attraction Effect in Decision Making: Superior Performance by Older Adults. P. Verhaeghen, C. Basak, Aging and Switching of the Focus of Attention in Working Memory: Results from a Modified N-Back Test. D. Bunce, A. Macready, Processing Speed, Executive Function, and Age Differences in Remembering and Knowing. T. Hedden, G. Lautenschlager, D.C. Park, Contributions of Processing Ability and Knowledge to Verbal Memory Tasks Across the Adult Lifespan.