560 



SCIENCE 



[Vol. LV, No. 1430 



psychic correlation" — a term whicli I have pro- 

 posed as much preferable to psychophysical 

 parallelism — in the domain of color. 



In a recent discussion of my color theory 

 {Am. J. Physiol. Optics, 1920-21) it is main- 

 tained that it would be more "advanced" to 

 regard as of '"prime importance" the cortical 

 processes : "It appears to me that the Ladd- 

 Pranklin theory postulates the existence in the 

 retina of conditions of sensation of the sort 

 required for the processes in the cerebral cor- 

 tex which directly underlie the visual con- 

 sciousness, but which are not required and 

 probably do not exist in the case of the retina." 

 In reply to this it is only necessary to point out 

 that if a "mechanism of defect" (such as would 

 result in loss of consciousness for the red- 

 greens and the yellow-blues) is found to occur 

 in any part of the light-sensation chain (rods 

 and cones, bipolar cells, third neurons, corpora 

 quadrigemina, optic thalamus, cortex) that de- 

 fect cannot be recovered from in any one of 

 the later stations of the nerve impulse — if B 

 and G have once reverted into Y, and T and B 

 into W, anywhere in the visual circuit, it is not 

 necessary to provide for their doing it again 

 in the cortex; on the other hand, if this defect 

 has not happened lower down — if a separate 

 "blue" and "yellow" have successfully reached 

 the cortex — it is improbable that Nature, out 

 of pure Bosartigkeit, should have introduced in 

 the cortex a mechanism for their extinction.^ 



V. Kries has objected that in my theory it is 

 not explained how the same sensation of white- 

 ness should be mediated directly in the rods 

 and in the more highly developed cones out of 

 a physical mixture of red, green, and blue 

 lights, but, as I have pointed out above, this is 

 exactly what my theory does explain. 



It has been called to my attention that several 

 of the psychologists, while practically adopting 

 my theory of color sensation, express the 

 opinion that I have given no explanation 

 of the sensation of black. But that is not 

 the case; I have not, it is true, discussed black 

 very frequently, and that, I believe, for two 

 reasons. (1) It is very simple — it has no con- 

 nections with any other of the color-sensations. 



s I discuss this point more fully in the Psycho- 

 logical Review, May, 1922. 



The reason that color "theory" is so important, 

 and has been so contended over, is that the 

 facts of color (excluding black) are so very 

 mysterious : why do we fail to see the yellow- 

 blues and the red-greens, and why do we get, 

 respectively, ivhite and yelloiv in their place? 

 Blackness stands by itself — it has no such 

 queer relations with any of the other colors. 

 Black and white, for instance, are not a dis- 

 appearing color pair; they give us the series 

 of black-whites, or greys. Black, being a sen- 

 sation attached to zero stimulation — not a light 

 sensation but a non-light sensation — is nat- 

 urally (since zero has one value only) a sensa- 

 tion of only one degree of subjective intensity; 

 the series of greys comes from changing the 

 subjective intensity of their white constituent 

 only. A blue-green of a given proportion of 

 blueness and greenness we can see in dozens of 

 different intensities; not so a grey. Give a 

 certain grey a higher illumination and you 

 change the quality as well as the brightness of 

 your black-white blend. Professor G. E. 

 Miiller has dwelt upon this latter fact, but he 

 has given a wrong interpretation of it; Wundt 

 also, although his theory of color is negligible 

 (and has been neglected), puts this situation 

 correctly. It is easily accounted for on my 

 theory. 



A fuller account of the Development Theory 

 of Color Sensation will be found in most of the 

 recent books on psychology, — as Calkins, Judd, 

 Angell, Breese, Watson, Warren and Wood- 

 worth. I have discussed it also in the Psycho- 

 logical Review, 23, 1916, and 29, 1922; in the 

 Am. Cyclop, of Ophthalmology, 1913; in the 

 Dictionary of Philosophy and Psychology ; in 

 Mind. 1892, 1893, and in Science, 22, pp. 

 18-19. In the last two places I have discussed 

 its fundamental difference from the theory of 

 Bonders. My theory has been taken over by 

 Sehenck without due acknowledgment, as has 

 been pointed out for me by v. Briicke (Zentrlbl. 

 f. Physiologie, 1905). It has suffered from not 

 having been criticised enough; some criticism 

 of it by V. Kries and by Troland I have dis- 

 cussed very fully in Practical Logic and Color 

 Theories {Psychological Beview, May, 1922). 



Christine Ladd-Feanklin 

 Columbia Universitt 



