UC San Diego

Recent evidence suggests that Parkinson's disease (PD) may be associated with greater impairment in visuospatial working memory as compared to visual object working memory. The nature of this selective impairment is not well understood, however, in part because successful performance on working memory tasks requires numerous cognitive processes. For example, the impairment may be limited to either the encoding or maintenance aspects of spatial working memory. Further, it is unknown at this point whether PD patients' selective impairment in spatial working memory generalizes to other tasks of spatial cognition. The present study investigated these issues by comparing the performance of nondemented patients with PD and normal control participants on a series of experiments that were designed to independently evaluate visuospatial and visual object cognition. Experiment 1 was composed of working memory conditions that differed only in what the participant was instructed to remember: locations or shapes. Encoding and maintenance aspects of performance were investigated by measuring accuracy over variable delays. Experiment 2 used an inhibition of return (IOR) task that has been demonstrated to measure spatial- and object-based components of inhibitory attention. Experiment 3 was composed of analogous location and shape discrimination conditions that did not have a working memory component. Group differences on the individual experiments were analyzed using repeated measures analysis of variance designs to test the overarching hypothesis that spatial-based cognition is more impaired than object- based cognition in PD. In Experiment 1, the patients demonstrated impairment in the encoding of spatial-based information, but were able to normally maintain that information over a 10-second delay. The reverse pattern was observed on the object working memory condition in that only maintenance processes were impaired. In Experiment 2, the patients also demonstrated a selective spatial impairment in that they showed reduced spatial- based IOR, while object-based IOR was intact. The results of Experiment 3 revealed that spatial-based visual discrimination was not more impaired than object-based visual discrimination, indicating that selective spatial deficits on higher-level visuocognitive tasks cannot be entirely attributed to a general impairment in spatial cognition. Rather, the selective spatial deficit appears to be limited to encoding and inhibitory attentional processes