ACT-R: A higher-level account of processing capacity

We present an account of processing capacity in the ACT-R theory. At the sy mbolic level, the number of chunks in the current goal provides a measure o f relational complexity. At the subsymbolic level, limits on spreading acti vation, measured by the attentional parameter W, provide a theory of proces sing capacity, which has been applied to performance, learning, and individ ual differences data.