Preserved learning and retention of pattern-analyzing skill in amnesia: dissociation of knowing how and knowing that.

Amnesic patients acquired a mirror-reading skill at a rate equivalent to that of matched control subjects and retained it for at least 3 months. The results indicate that the class of preserved learning skills in amnesia is broader than previously reported. Amnesia seems to spare information that is based on rules or procedures, as contrasted with information that is data-based or declarative--"knowing how rather than "knowing that." The results support the hypothesis that such a distinction is honored by the nervous system.