%0 Journal Article
%@ 1932-6203
%A Rider, AT
%A Henning, GB
%A Stockman, A
%D 2019
%F discovery:10079526
%J PLoS One
%N 8
%T Light adaptation controls visual sensitivity by adjusting the speed and gain of the response to light
%U https://discovery.ucl.ac.uk/id/eprint/10079526/
%V 14
%X The range of c. 1012 ambient light levels to which we can be exposed massively exceeds the  <103 response range of neurons in the visual system, but we can see well in dim starlight  and bright sunlight. This remarkable ability is achieved largely by a speeding up of the visual  response as light levels increase, causing characteristic changes in our sensitivity to different rates of flicker. Here, we account for over 65 years of flicker-sensitivity measurements  with an elegantly-simple, physiologically-relevant model built from first-order low-pass filters  and subtractive inhibition. There are only two intensity-dependent model parameters: one  adjusts the speed of the visual response by shortening the time constants of some of the filters in the direct cascade as well as those in the inhibitory stages; the other parameter  adjusts the overall gain at higher light levels. After reviewing the physiological literature, we  associate the variable gain and three of the variable-speed filters with biochemical processes in cone photoreceptors, and a further variable-speed filter with processes in ganglion  cells. The variable-speed but fixed-strength subtractive inhibition is most likely associated  with lateral connections in the retina. Additional fixed-speed filters may be more central. The  model can explain the important characteristics of human flicker-sensitivity including the  approximate dependences of low-frequency sensitivity on contrast (Weber’s law) and of  high-frequency sensitivity on amplitude (“high-frequency linearity”), the exponential loss of  high-frequency sensitivity with increasing frequency, and the logarithmic increase in temporal acuity with light level (Ferry-Porter law). In the time-domain, the model can account for  several characteristics of flash sensitivity including changes in contrast sensitivity with light  level (de Vries-Rose and Weber’s laws) and changes in temporal summation (Bloch’s law).  The new model provides fundamental insights into the workings of the visual system and  gives a simple account of many visual phenomena.
%Z This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.  http://creativecommons.org/licenses/by/4.0/