and could be a result of deafferentation to these particular underlying areas. PD is a progressive neurodegenerative disorder. It is associated with the degeneration of neurons in the substantia nigra and locus coeruleus. Clinical symptoms of PD include tremor at rest, rigidity, akinesia, difficulty initiating or maintaining movement, and slowed movement. One of the primary findings from various studies suggests that there are impairments in visual selective attention in PD patients. For example, PD patients show abnormal performance on the Stroop task, and impaired ability to selectively attend to targets among distractors, or to attend selectively to visual displays while simultaneously performing other tasks. The neuropathology of this disease is consistent with these attentional deficit. While not all individuals with PD also develop dementia, it is a common comorbidity and affects the same areas of visual selective attention impaired in individuals with MCI, AD, and DLB. Visual perception encompasses several component processes, including the ability to selectively attend to a relevant stimuli while being able to effectively ignore irrelevant distractor information. This deficit in PD patients also relates to a deficit in overall attentional processes. Degeneration of the substantia nigra is implicated in the cause of Parkinson's disease. These regions of the basal ganglia are also implicated in attentional processes, especially visual selective attention. It is therefore suggested that deficits in the basal ganglia and related regions may lead to impaired visual selective attention in these individuals. Individuals with PD may be impaired in their ability to attend selectively for several different reasons. These patients may show deficits in their ability to inhibit the processing of the irrelevant information which is presented, therefore there are enabling the irrelevant information to interfere with their processing of the target information; or PD patients may indeed be able to inhibit the processing of the irrelevant stimuli, but showed impairments in maintaining the selectivity of their attention to the relevant stimuli, supported by an abnormally rapid disengagement of attention from the location at which a visual cue last appeared. References Dementia Physiological psychology Cognitive neuroscience