Impaired verbal category learning in amnesia.

Amnesic patients and controls listened to verbal descriptions of imaginary animals and then classified novel descriptions according to whether they belonged to the studied category. Controls performed well, but the amnesic patients did not acquire categorical knowledge. These findings contrast with previous demonstrations of intact category learning by amnesic patients for dot patterns, artificial grammars, and cartoon animals. It appears that category knowledge can be acquired implicitly when training exemplars are presented visually and when the similarities among items can be readily perceived. Verbal category learning requires the extraction and retention of meaning from training exemplars that are separated in time and may make demands on declarative memory that are beyond the capacity of amnesic patients.