to shift attention from feature or location to another. In this study, it was found that DLB patients in this task performed markedly worse than both AD patients and healthy controls in the single-target condition. This suggests that the perceptual filtering component of selective attention is significantly impaired in DLB. Difficulties in discrimination in DLB patients for visual stimuli may be due to reduced ability to select and encode relevant or important information in the target search. DLB patients’ general slowness could have increased perceptual interference due to masking from distractors, and target selection and processing (in tasks such as the RSVP task) must be performed under time pressure. Another study by Calderon et al. compared patients with DLB and AD to evaluate attentional and visuoperceptual abilities, executive function, and semantic and episodic memory, using specific neuropsychological tests. To test visual selective attention, a map search task was used, in which participant must identify target symbols from competing distractors. Results suggested that visual selective attention in DLB was more significantly impaired than AD, although AD patients were significantly more impaired than healthy controls. This study confirms that DLB patients have greater impairment of attentional and visuoperceptual abilities, attentional and executive tasks, and a large number of patients with DLB were unable to complete some measures of visual selective attention such as the Stroop task. It is therefore apparent that attentional processes are significantly more impaired in DLB patients than AD patients, especially in their visual selective attentional abilities. There appears to be a global breakdown in attention of all aspects in patients with DLB, as highlighted by this study. A possible cause for this is the hypothesis that severe cholinergic deletion may be the underlying component in the attention deficit in DLB. Parkinson's disease Parkinson's disease (PD) is characterised by degeneration of the substantia nigra within the basal ganglia and the locus coeruleus. These regions are implicated in attentional processes, particularly visual selective attention. Animal research and positron emission tomography (PET) studies have shown the role of the basal ganglia in selective attention processes, suggesting that deficits in these areas may lead to impaired attentional functions in PD patients. It is also possible that other brain regions, such as the frontal lobes or the superior colliculus, which are connected to the basal ganglia, underlies attentional deficits in PD patients. Damage to these areas may result in impairment in attentional functioning,