(514 RADIATION BIOLOGY 



like the classical red "fundamental sensation curve" of Konig. Simi- 

 larly an interval of 2 sec yields a curve similar to the fundamental green, 

 and 3 sec yields the fundamental blue curve. 



Motokawa has applied his new technique to the exploration of a num- 

 ber of other visual functions. Color blindness, for example, was revealed 

 by an absence of the red function for a protanope and of the green one 

 for a deuteranope. In the periphery an independent yellow function was 

 found for normal trichromatic vision. 



Contrast effects have also been studied by Motokawa. The most 

 elaborate experiments of this kind were some in which various geometrical 

 figures were introduced with yellow light in the form of line drawings 

 on a screen. After a figure was exposed, a small standard patch of white 

 light was applied at a point near the boundary of the original figure. 

 Finally an electrical stimulus was presented at an interval of 1.5 sec after 

 the standard patch. The electrical threshold was found to vary with the 

 characteristics of the geometrical figure. In particular, it was found that 

 the electrical threshold varied systematically with the nearness of the 

 standard flash to the boundary of the figure. This is called the "induc- 

 tive effect" of the boundary fine. 



The inductive effects have been explored for regions around the bounda- 

 ries of squares, circles, Landolt rings, vernier displacement figures, broken 

 fines, and the classical figures for demonstrating visual illusions. Briefly 

 the results may be summarized as follows: Any region of discontinuity or 

 sharpness of contour yields a steep gradient of induction for the region 

 around it. Thus broken lines have a stronger inductive effect than solid 

 lines do, and the gap in vernier or Landolt objects is accentuated in the 

 region surrounding it. Visual illusions are consistent with the inductive 

 effects that they appear to eficit. 



Motokawa concludes that he has demonstrated a direct physiological 

 basis for perceptual phenomena that have long been described subjec- 

 tively by gestalt psychologists and others. One may certainly question 

 this interpretation on the grounds that the electrical thresholds them- 

 selves are subjectively determined, being based upon the appearances of 

 phosphenes as reported by the observer. Certainly the most basic of 

 these very provocative experiments merit repetition in other laboratories. 

 Only when there is a more thorough groundwork of facts on the process 

 of enhancement will we be in a position to interpret the findings as they 

 apply to such comphcated functions as color discrimination and visual 

 illusions. 



SUMMARY AND CONCLUSIONS 



1. Electrical phenomena in vision include the stimulation and the 

 recording of neural responses at any point within a visual system. 



2. There is a resting potential that, in the vertebrate eye, amounts to 



