title: Visual Priming and Visual Hallucinations in Parkinson's Disease. Evidence for Normal Top-Down Processes.
abstract: BACKGROUND
  Visual hallucinations (VH) are common in Parkinson's disease (PD) and are associated with increased morbidity and mortality. Current explanations for VH in PD suggest combined impairments in top-down attentional and bottom-up perceptual processes, which allow the passive "release" of stored images. Alternative models in other disorders have suggested that top-down factors may actively encourage hallucinations. In order to explore the interaction between top-down and bottom-up visual processing in PDVH, we developed novel experimental priming tasks in which top-down verbal cues were used to prime the bottom-up recognition of partial or ambiguous pictures.
  
  
  METHODS
  Two groups of PD participants with (PD + VH, n = 16), and without VH (PD - VH, n = 20) were compared to a group of healthy older adults (NC, n = 20) on 3 novel measures of visual priming.
  
  
  RESULTS
  All tasks showed significant priming effects. The PD + VH group was more impaired at accurately identifying silhouette and fragmented images compared to the PD - VH group. There were no differences in priming between the 2 PD groups.
  
  
  CONCLUSIONS
  The study showed that VH in PD are not associated with relatively greater top-down activation, and that the interaction between top-down and bottom-up processes is intact.
authors.affiliation: Mental Health Services for Older People, Sandwell Park Hospital, Hartlepool, England sarahstraughan@hotmail.co.uk.
authors.forename: Sarah
authors.initials: S
authors.lastname: Straughan
authors.affiliation: Clinical Psychology Department, Bensham Hospital, Gateshead, England.
authors.forename: Daniel
authors.initials: D
authors.lastname: Collerton
authors.affiliation: School of Psychology, Newcastle University, Newcastle upon Tyne, England.
authors.forename: Vicki
authors.initials: V
authors.lastname: Bruce
mesh_terms: D000328:Adult; D000368:Aged; D001288:Attention / Q000502:physiology*; D016022:Case-Control Studies; D003463:Cues; D005260:Female; D006212:Hallucinations / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000150:complications / Q000523:psychology*; D010468:Perceptual Disorders / Q000209:etiology*
keywords: Parkinson disease; bottom-up processing; hallucinations; perception; top-down processing