Recent evidence raised the possibility that the neostriatum and the corticostriatal circuits could play an important role in semantic categorization. In this study, we examined the electrophysiological correlates of natural scene categorization in Huntington's disease (HD) patients and their asymptomatic relatives who were Huntington's disease mutation carriers (HDC). Event-related potentials were recorded in HD patients, HDC subjects, and age-matched control subjects using a natural scene categorization task. The subjects had to decide whether a briefly presented image contained animals or no animals. Concerning the N1 component (150-250 ms), the mean amplitudes were more negative for nonanimal scenes as compared with stimuli containing animals at all electrode sites in the control group and at all but the lateral temporal electrode sites (T3, T4) in the HD group. Between-group comparison demonstrated that the N1 amplitudes were significantly smaller for both kinds of stimuli in the HD group in spite of a normal primary occipital component (P100). The HDC subjects were not significantly different from the controls concerning the N1 amplitudes. These results suggest that perceptual (N1) processes related to the categorization of natural scenes are specifically impaired in HD. The findings are in agreement with the hypothesis emphasizing the importance of neostriatal mechanisms in human categorization functions.