THE FIELD OF VISION FOR COLOURS 



69 



The limits of the colour fields vary not only with the intensity of 

 the light, but also with the saturation of the colour, and, above all, 

 the size of the object. If these are sufficiently great colours may be 

 recognised, almost, if not quite, at the extreme periphery (Bonders, 

 Landolt). 



As already mentioned only the foveal region gives the unadulterated 

 photopic reactions, unless the eye is very completely adapted to light, 

 so that all traces of scotopia are eliminated from the peripheral field. 



70 



Fig. 24. Perception of colours in different parts of the field of vision. Abscissae, de- 

 grees to the nasal side of the fovea {O) ; ordinates, maximum distance at which the colour 

 is perceptible in a coloured paper 2 mm. square. (Charpentier.) 



Ordinary observations with the perimeter do not afford accurate details 

 for comparison. If light adaptation is rendered as complete as possible 

 by exposure to bright sunlight many points of interest are elicited. 

 Under these circumstances it appears — within the limits of experimental 

 error — that colour matches, spectral or composite, which hold good for 

 the fovea remain good when viewed eccentrically, but though the 

 matches remain matches the values alter, the colours changing in the 

 raid-peripheral region, and becoming colourless in the extreme periphery. 

 It may therefore be concluded that in the phofopic eye peripheral vision 

 differs from central vision only in the direction of a diminution in sensi- 

 bility, and not in the direction of a change in character of sensation. 

 Further, all colour mixtures which appear colourless by central 

 vision remain colourless by peripheral vision. Allowance must, however 



