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He does not assign a role to the n, o, and r ganglion cells of Polyak and 

 has to assume two types of cones, although there is no direct evidence 

 for the latter. The model is successful in using three basic photosensi- 

 tive pigments which are acted on in a positive manner as demanded by 

 the tricolor stimulus theories of Young and Helmholtz. It also has all 

 the advantages of the opponents theories in having B-Y, R-G, W-S 

 antagonists in the response of the retinal nerves. One must assume, 

 as do other opponents theories, similar antagonistic actions in the 

 central nervous system in analyzing conflicting information. 



In addition to the histological and psychophysical evidence strongly 

 supporting this model, several other types of detailed subjective informa- 

 tion can be correlated using the theory of color vision outlined above, 

 In particular, the evidence for the role of the rods in blue color vision, 

 experiments with test patches of color on light-adapted eyes, kinetic 

 experiments, and abnormal vision will be discussed. 



The role of the rods in scotopic vision is agreed upon quite generally. 

 The absorption curve of the pigment rhodopsin in the rods is similar to 

 the scotopic luminosity curve, and many indirect lines of evidence 

 support the role of the rods in scotopic vision. The connection between 

 the rods and blue vision is supported by subjective observation. For 

 example, green and blue appear brighter peripherally where there are 

 more rods, whereas yellow and red are brighter at the fovea. Similar 

 support comes from studies of the narrow range of intensities between the 

 scotopic threshold and the threshold at which color is identified. Sub- 

 jects usually experience a sensation of gray in this achromatic range. 

 The size of achromatic range is greater for red than for blue. Because 

 the rods alone are stimulated in the achromatic range, this suggests that 

 the rods p are intimately connected with blue vision. 



Other types of data concerning the thresholds for color vision come 

 from studies using light-adapted eyes and narrow test patches illumin- 

 ating 1° or 2° of the visual field. Many variations have been tried using 

 eyes adapted to various colored lights and using the same or other 

 colored lights as test patches. Other experiments have presented test 

 patches in different parts of the visual field. All of the experiments 

 indicate at least six characteristic absorption curves. Attempts to assign 

 these curves to different receptors implies six pigments. No evidence 

 from either histology or biochemistry can be interpreted to make six 

 pigments a reasonable number. By contrast, the scheme diagrammed 

 in Figure 2 is in accord with at least six spectra if the experiments are 

 really fatiguing the neural elements as well as the receptors. If one 

 admits different fatigue curves for cell types p, 8, t, d, e, f, h, m, and p, 

 one can predict that there may be a very large number of absorption 

 curves for light-adapted eyes under varying conditions. 



