ABSTRACT
The precision with which items are encoded in working memory and attention decreases with the number of encoded items. Current theories typically account for this “set size effect” by postulating a hard constraint on the allocated amount of encoding resource. While these theories have produced models that are descriptively successful, they offer no principled explanation for the very existence of set size effects: given their detrimental consequences for behavioral performance, why have these effects not been weeded out by evolutionary pressure, by allocating resources proportionally to the number of encoded items? Here, we propose a theory that is based on an ecological notion of rationality: set size effects are the result of a near-optimal trade-off between behavioral performance and the neural costs associated with stimulus encoding. We derive models for four visual working memory and attention tasks and show that they account well for data from eleven previously published experiments. Moreover, our results suggest that the total amount of resource that subjects allocate for stimulus encoding varies non-monotonically with set size, which is consistent with our rational theory of set size effects but not with previous descriptive theories. Altogether, our findings suggest that set size effects may have a rational basis and highlight the importance of considering ecological costs in theories of human cognition.
