title: "Cognitive" visual acuity estimation based on the event-related potential P300 component.
abstract: OBJECTIVE
  An objective assessment of sensory and sensuo-cognitive function, based on physiological signals rather than on the behavioral response of a patient, is often advisable, albeit challenging. Evoked potentials are frequently used as an objective measure, but usually fail to detect defects beyond primary sensory areas, including those of psychogenic origin. Here we assess whether the event-related P300 component may be used to measure "cognitive" visual acuity.
  
  
  METHODS
  A visual oddball paradigm was used to elicit P300 responses in subjects with normal or artificially blurred vision. Probe stimuli consisted of infrequently presented gratings with spatial frequencies in the range of 2.2-16.2 cycles per degree, which could be either target or non-target stimuli depending on their orientation. Frequent stimuli were homogeneously grey fields.
  
  
  RESULTS
  Without blur, rare stimuli of all spatial frequencies produced reliable P300 responses. Blur abolished the P300 to fine gratings consistently in 10 of 11 subjects. The drop in P300 amplitude was steep, rather than gradual, between visible and invisible gratings.
  
  
  CONCLUSIONS
  The P300 is sensitive to identify the resolution threshold and thus may serve as a tool for estimating acuity in cases of visual impairments.
  
  
  CONCLUSIONS
  The study presents a tool for the objective assessment of acuity in cases of higher-level visual impairments. The concept can most likely be extended to other sensory modalities.
authors.affiliation: Sektion Funktionelle Sehforschung, Univ.-Augenklinik Freiburg, Killianstr. 5, 79106 Freiburg, Germany. Electronic address: sven.heinrich@uniklinik-freiburg.de.
authors.forename: Sven P
authors.initials: SP
authors.lastname: Heinrich
authors.affiliation: Sektion Funktionelle Sehforschung, Univ.-Augenklinik Freiburg, Killianstr. 5, 79106 Freiburg, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Marhöfer
authors.affiliation: Sektion Funktionelle Sehforschung, Univ.-Augenklinik Freiburg, Killianstr. 5, 79106 Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Bach
mesh_terms: D000328:Adult; D000465:Algorithms; D003071:Cognition / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods; D018913:Event-Related Potentials, P300 / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D012044:Regression Analysis; D013028:Space Perception / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult