Signal, Noise, Performance, and Age

Ten years ago, it seemed reasonable to summarize two decades of research on the age changes in central mechanisms affecting performance under four main headings: slowing of perception and action, increased disruption of short-term memory by any shift of attention, difficulty in searching material in long-term memory, and difficulty in coping with certain kinds of complexity. Theories under these four headings are reexamined in light of recent findings which imply that older people have a reduced signal-to-noise ratio in the brain but at the same time a spontaneous tendency to adopt strategies which optimize performance. This approach accounts directly for longer times taken in discrimination and some choice reaction tasks, and indirectly for at least some of the greater tendency of older people to monitor their responses. A model is proposed which applies the same approach to memory. In terms of this model, poor performances in both short- and long-term memory are due to failure to transfer items from primary to secondary memory and to the weakness of traces established in long-term memory. The model raises some as yet unanswered questions about the precise manner in which complex relationships between signals and responses are handled.