title: Contrast adaptation in human retina and cortex.
abstract: OBJECTIVE
  Although cortical contrast adaptation has been extensively studied with both psychophysical and electrophysiological techniques, little is known about retinal contrast adaptation in humans.
  
  
  METHODS
  Retinal and cortical long-term contrast adaptation was assessed with simultaneous measurement of pattern electroretinogram (PERG) and cortical visual evoked potentials (VEPs). This study involved three approaches: sampling of the contrast transfer function from 2.7% to 98% with adaptation to high (98%) and low (7.3%) contrasts, linearity of adaptation effects, and transfer of contrast adaptation between parallel and orthogonal grating orientations.
  
  
  RESULTS
  Contrast adaptation affected retinal and cortical recordings quite differently. The VEP showed a sigmoid contrast transfer function, which was shifted toward higher contrasts (by a factor of 1.9), whereas amplitudes at higher test contrasts were enhanced to 127%. The PERG decreased in amplitude to approximately 90%, and the latency was significantly reduced by 4 to 6 msec (P < 0.05). All measured effects were linear with adaptation contrast. Orientation played no role in the PERG results, whereas the VEP was enhanced to 125% when tested parallel and to 150% when tested orthogonal to adaptation.
  
  
  CONCLUSIONS
  VEP results confirm and extend previous findings and fit well with single-cell recordings. The PERG findings suggest that retinal contrast adaptation occurs and mainly operates in the temporal domain, comparable to rapid gain-control findings in cats and primates.
authors.affiliation: Elektrophysiologisches Labor, Universitäts-Augenklinik, Freiburg, Germany.
authors.forename: T S
authors.initials: TS
authors.lastname: Heinrich
authors.forename: M
authors.initials: M
authors.lastname: Bach
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology*; D004596:Electroretinography; D005074:Evoked Potentials, Visual; D006801:Humans; D010364:Pattern Recognition, Visual; D012160:Retina / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*