Patterns of conversational gestures were analysed in subjects with Alzheimer's type dementia (DAT), fluent aphasics with a primarily lexical-semantic deficit (FA) and normal subjects. The FA subjects produced twice as many gestures as the normal participants with a normal percentage of gestures that showed semantic features of the lexical items in concurrent speech (iconic). A comparable lexical-semantic deficit together with a deficit in conceptual organisation of information corresponded to a normal gesturing rate in the DAT subjects; however, the percentage of iconic gestures was reduced. Gestures were also analysed in four DAT patients whose communicative performance indicated primarily lexical-semantic (2 patients) or conceptual deficit (2 patients). In the two DAT patients with lexical-semantic deficit, the gesture pattern was like that of the FA patients; in the other two, the pattern of the DAT group was observed. These results agree with previous findings that DAT "empty" speech corresponds to reduced production of gestures showing semantic features (Glosser et al., 1998). However, the comparison between DAT with primarily lexical-semantic or conceptual deficits indicates that the nature of the cognitive impairment underlying poor information content and lack of reference in DAT discourse constrains the production of conversational gestures by patients with this disease. These findings are at variance with the hypothesis of parallel dissolution of speech and gestures in language disorders after brain damage (Cicone et al., 1979; McNeill, 1992; Glosser et al., 1998).
