title: Missing colours (fehlfarben) of deuteranopes and extreme deuteranomalous observers.
abstract: The directions of lacking colur discrimination (Fehlfarben) were determined within the framework of the three-dimensional colour space for four deuteranopes and two extreme deuteranomalous observers.
  
  
  RESULTS
  (a) intra-individually, there is no significant correlation between the slope of the isochromatic lines and hue; (b) inter-individually, their Fehlfarben, respective their copunctual points, do not appear to stem from one population; (c) the extreme deuteranomalous do not reveal a trend towards or awau from protanopia.
mesh_terms: D000293:Adolescent; D000818:Animals; D003119:Color Perception Tests; D003117:Color Vision Defects / Q000503:physiopathology*; D000882:Haplorhini; D006801:Humans; D008297:Male