Facts, rules, and procedures in normal calculation: evidence from multiple single-patient studies of impaired arithmetic fact retrieval.

This article presents results from multiple single-case studies of brain-damaged patients with impairments in retrieval of arithmetic facts (i.e., "table" facts such as 8 x 7 = 56). The results provide a basis for exploring the types of knowledge implicated in simple arithmetic performance, the internal representations for the various knowledge types, the processes operating upon these representations, and the ways in which the representations or processes may be disrupted by brain damage.