A neural mechanism improving visual acuity by contrast enhancement, a study of foveal vision.
Analysis of synaptic connections between neurons in the retina (Sjöstrand, 1958, 1974, 1989, 1990, 1998a,b,d) has revealed a pattern of connections between rods, cones and bipolar cells that shapes neural interaction to generate spatial brightness contrast enhancement, explaining the Mach band phenomenon (Mach, 1865). Using the Mach band effect at boundaries between fields of different brightness it was revealed that the phenomenon applies to foveal vision. The contrast enhancing distortion of brightness was confined to zones, the width of which approached visual resolution. The distortion also applied to boundaries between fields of different colors when differing in brightness. The distortion involved an achromatic component. The quality of vision deteriorated with decreasing illumination at the same rate enhancement of contrast faded. Spatial brightness contrast enhancement is therefore a major factor contributing to visual acuity and fading of enhancement explains the deterioration of the perceived image at low illumination.
Sjöstrand
E S
ES
University of California, Los Angeles 90024, USA. fsjostra@ucla.edu
D015350:Contrast Sensitivity / Q000502:physiology*; D005584:Fovea Centralis / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D009474:Neurons / Q000502:physiology*; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D014787:Vision Tests / Q000379:methods; D014792:Visual Acuity / Q000502:physiology*