592 RADIATION BIOLOGY 



electroretinogram data on dark adaptation are therefore thought to 

 reflect primarily the restorative process in retinal rod receptors, uncom- 

 plicated by cone-receptor activity or the activity of higher centers in the 

 visual system. 



Effects of Colored Light. Color vision is obviously dependent on the 

 ability of the eye to respond differentially to stimulation by lights of 

 various wave lengths. Several investigators have therefore attempted to 

 obtain specific electrical responses of the human eye to colored lights. 

 Motokawa and Mita (1942), using electrodes located on the skin adjacent 

 to the eyeball, were able to observe an "a;-wave," consisting of a rapid 

 spike in response to red, which preceded the regular 6-wave of the electro- 

 retinogram. It is probable that the conditions of recording were such 

 that other specific effects were not observed. 



Adrian (1945, 1946), using a moist thread electrode on the eye and a 

 capacitance-coupled amplifier, was able to obtain a more comprehensive 

 set of records showing responses to colored lights. He found that deep 

 red light produced only a small but rapidly developing action potential 

 in the eye of man or monkey. Orange-red light yielded a double wave 

 consisting of this rapid component plus the regular 5-wave. Lights of 

 shorter wave lengths produced more typical fo-waves with little evidence 

 of the rapid component. Adrian concluded that the rapid response was 

 that of a photopic or high-level system, whereas the regular 6-wave arose 

 from the scotopic system on which we depend for seeing at night. He 

 was able to modify the two differentially by using appropriate conditions 

 of adaptation, flicker, and retinal area. Monnier (1949) confirmed some 

 of the observations of Adrian on specific wave-length effects. 



Riggs ct al. (1949) obtained records of the human action potential for 

 various wave lengths and intensities of stimulating light. Using contact- 

 lens electrodes and a direct-coupled amplifier, they obtained results that 

 agreed with those of Adrian to the extent that two components were 

 observed. The fast one, however, was much less prominent than the 

 one described by Adrian. A spectral-sensitivity curve was computed on 

 the basis of human 6-wave responses. It was shown to agree fairly well 

 with a psychophysically determined scotopic-sensitivity curve except at 

 the blue end of the spectrum. Blue light was unexpectedly high in its 

 ability to elicit a 6-wave. 



The a--wave of Motokawa and the fast component observed by Adrian 

 and others may reflect either a specific response to red light or a more 

 general response of the photopic or cone-receptor visual system. If the 

 latter, there may be some sort of interference that prevents the wave 

 from showing itself optimally on stimulation by light at 555 m/z, a wave 

 length of light usually associated with the greatest photopic effect. 



We may conclude that wave-length specificity is certainly present in 

 the human action potential. There is no clear evidence as yet that color- 



