Performance of Parkinson's disease patients on the Visual Search and Attention Test: impairment in single-feature but not dual-feature visual search.

Nondemented patients with Parkinson's disease (PD) and a group of age and education matched controls were administered a modified version of the Visual Search and Attention Test (VSAT). This task measures subjects' speed at localizing letter or symbol targets based on either a single-feature or a dual-feature search. Three indices were derived from the VSAT: (a) the amount of time taken to complete each of the trials (completion time), (b) the number of target items not crossed out (omissions), and (c) the number of nontarget items crossed out (commissions). The results indicated that, in terms of completion time, the PD patients were impaired on the single-feature search conditions but not on the dual-feature search conditions, suggesting that PD patients are impaired in selective attention processes. It was also found that the number of target items omitted by the normal controls on the VSAT varied as a function of the nature of the target (letter or form) and the search requirements (single-feature or dual-feature search), whereas the number of targets omitted by the PD patients was not affected by these factors. Correlational analyses suggested that the three measures derived from the VSAT assessed different components of attentional performance in these patients. Overall, the results of this study suggest that the VSAT can be used to detect subtle attentional impairments in nondemented PD patients, and that the pattern of their impairment on this clinical test is similar to that found on experimental attentional measures.