Authors:

ROGERS, T.T.R., Lambon Ralph, M.A., HODGES, J.R. & PATTERSON, K.

Reference:

Year of publication:

2002

CBU number:

5167

Abstract:

We tested patients with semantic dementia on novel object-decision and lexical-decision tasks that varied the regularity of target and distractor stimuli. In the object-decision task, patients saw line drawings of real- and chimeric-animals side-by-side, and were asked to decide which was real. In one condition, the real animal was more typical-looking than the chimera (Regular Targets or RT condition); in a second condition, the reverse was true (Irregular Targets or IT condition). The lexical decision task employed a similar logic: patients saw a real word and a nonword pseudo-homophone of the target side-by-side, and were asked to decide which was real. In the RT condition, real words were more orthographically regular than nonwords; the reverse was true in the IT condition. Performance in both tasks was modulated by the extent of the patients' semantic impairment; but regardless of severity, patients were much less successful in the IT than the RT conditions. In the object-decision task, severe patients were at chance for IT stimuli, but above 80% correct for RT stimuli. In the lexical-decision task, severe patients were often below chance in the IT condition, but continued to score near ceiling in the RT condition. The data are consistent with a theory of object- and word-recognition in which semantics provides a ``cognitive glue'' that assists discrimination of meaningful from nonmeaningful stimuli. Good performance on such recognition tasks can still obtain in the face of semantic degradation if and only if targets respect the surface structure of the domain and distractors do not.