title: Evidence for increased internal noise in migraineurs for contrast and shape processing.
abstract: OBJECTIVE
  Increased contrast-level dependent internal noise has been reported in migraine. This study aimed to investigate whether a general increase in internal noise impacted on other tasks thought to assess functioning in cortical area V1 and was evident in global contour coding (V4).
  
  
  METHODS
  Eleven migraineurs (six with aura) and 12 headache-free controls completed three psychophysical tasks: (i) contrast detection, (ii) discrimination of the angle of a spiral path and (iii) detection of deformation from circularity. Internal noise estimates were obtained using an N-pass method that compared responses to repeated presentations of identical stimuli. Internal noise results in inconsistent responses across different runs.
  
  
  RESULTS
  Migraineurs had significantly higher contrast thresholds when there was high external luminance noise. There were no other significant group differences in thresholds. Increased multiplicative noise associated with contrast processing was replicated and increased additive noise, which is independent of the visual input, was found for the global form task.
  
  
  CONCLUSIONS
  This study provides further evidence for increased multiplicative internal noise associated with contrast processing in migraineurs. However there is no generalised increase in internal noise in V1 as noise estimates for angular discrimination were normal. Increased additive internal noise was associated with the global shape task, co-occurring with increased efficiency.
authors.affiliation: School of Psychology, University of Western Australia, Australia.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Webster
authors.forename: J Edwin
authors.initials: JE
authors.lastname: Dickinson
authors.forename: Josephine
authors.initials: J
authors.lastname: Battista
authors.forename: Allison M
authors.initials: AM
authors.lastname: McKendrick
authors.forename: David R
authors.initials: DR
authors.lastname: Badcock
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008029:Lighting; D008881:Migraine Disorders / Q000150:complications / Q000503:physiopathology*; D008959:Models, Neurological; D010775:Photic Stimulation / Q000379:methods; D012684:Sensory Thresholds / Q000502:physiology; D014786:Vision Disorders / Q000209:etiology / Q000503:physiopathology*; D014795:Visual Pathways / Q000502:physiology*; D055815:Young Adult