COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 35 



method and apparatus under which they were obtained, and evaluate 

 them in the light of the widely different degrees of scientific insight 

 and of appreciation of the difficulties of the problem, which their spon- 

 sors display. 



All investigators agree that the central and paracentral regions of 

 the retina possess the keenest sensitivity to color; and all are agreed 

 that this acuteness diminishes in a more or less gradual and regular 

 manner towards the periphery. Moreover, the more recent workers 

 at least, are of the opinion that even the peripheral retina is not, strictly 

 speaking, color-blind. Its " color sense " may be so weak that a relatively 

 strong stimulation is required to call forth the whole manifold of sen- 

 sation qualities which it is capable of furnishing ; but that it may, under 

 appropriate conditions, furnish the same qualitative series as the* more 

 acute central regions, is no longer doubted. 



The difference of opinion as regards the mode of interpretation 

 which best fits these and other data is, after all, just what was to be 

 expected under the circumstances. For, so long as color theorists fail 

 to agree in their envisagement of the physiological process which con- 

 ditions the seeing of color, it is neither unnatural nor perhaps undesir- 

 able that different interpretations should be put upon the findings of 

 the various investigators. 



Any attempt to obtain a definite characterization of the decrease 

 ->f color sensitivity which is characteristic of indirect vision, or to define 

 the behavior of the peripheral retina in the presence of color stimuli, 

 reveals the existence of two distinct problems : What changes of color 

 occur, and where do they occur? Or, more specifically, (i) what are 

 the transitions of tone through which a color stimulus appears to pass, 

 during the movement of its image across the retina? And, (2) what 

 is the relative extension of the retinal zones within which the various 

 color stimuli appear in the different transitional tones ? 



(i) The first of these problems is obviously much more easy of 

 solution than the second. The factors which determine what changes 

 of tone shall take place in a given case, are evidently much less complex 

 than are those which determine the relative distance from the fovea at 

 which the changes shall appear. And since, moreover, the investigator 

 is concerned, in the former case, with the determination of absolute 

 values only, while in the latter case he has to do with relative values, it 

 becomes evident that the second problem is complicated by a multi- 

 plicity of co-operating factors. So long as the stimuli employed by the 

 investigator of absolute change of tone, possess a fair degree of satura- 

 tion and of brightness, so long as they subtend visual angles of moderate 



