Beyond resources: Formal models of complexity effects and age differences in working memory

We explore several alternative formal models of working memory capacity lim its and of the effect of ageing on these capacity limits. Three models test variations of resource accounts, one assumes a fixed number of free slots in working memory, one is based on decay and processing speed, one attribut es capacity limits to interference, and one to crosstalk between associatio ns of content and context representations. The models are evaluated by fitt ing them to time-accuracy functions of 16 young and 17 old adults working o n a numerical memory-updating task under varied memory-load conditions. Wit h increasing complexity (i.e., memory load), both asymptotic accuracy and t he rate of approach to the asymptote decreased. Old adults reached lower as ymptotes with the more complex tasks, and had generally slower rates. The i nterference model and the decay model fit the individual time-accuracy func tions reasonably well, whereas the other models failed to account for the d ata. Within the interference model, age effects could be attributed to the older adults' higher susceptibility to interference. Within the decay model , old adults differed from young adults by a higher degree of variability i n the activation of working memory contents.