Johannes Adolf von Kries (6 October 1853 – 30 December 1928) was a German physiological psychologist who formulated the modern “duplicity” or “duplexity” theory of vision mediated by rod cells at low light levels and three types of cone cells at higher light levels. He made important contributions in the field of haemodynamics. In addition, von Kries was a significant theorist of the foundations of probability.
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