Progressive loss of semantic memory in a case of Alzheimer's disease.

The breakdown of semantic memory in a patient with Alzheimer's disease was monitored by using a word-picture matching task. Performance deteriorated from a time when target pictures were selected virtually without error to a time when targets and semantically related distractor pictures were selected equally often. From this point, selection deteriorated rapidly to random. Knowledge of category membership and semantic features declined together over the same period. No consistency in item selection could be discerned, and successful selection in early tests was not influenced by either the name frequency or the familiarity of the target. The findings are argued to support a theory of access to semantic memory which is non-hierarchical.