Johannes Adolf von Kries (6 October 1853 – 30 December 1928) was a German physiological psychologist[1] 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.
[2][3] He made important contributions in the field of haemodynamics.
[4] In addition, von Kries was a significant theorist of the foundations of probability.
When von Kries was at Freiburg (1880–1924),[5] he was called to succeed Professor Emil Du Bois-Reymond as chair of physiology at the University of Berlin, but he declined.
[6] Von Kries has been called Helmholtz's "greatest German disciple".