Gradient detection and contrast transfer by the human eye.
D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D055095:Optics and Photonics; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010783:Photometry; D013028:Space Perception / Q000502:physiology*; D014785:Vision, Ocular; D014794:Visual Fields