MacNICHOL, WOLBARSHT, AND WAGNER 



m'i 



^Mlii•fflf«^■l*^ 



HOC 



mm 



600 



V50 



Fig. 5. Variation of response from a single ganglion cell with change in wave- 

 length of stimulus. Each record represents the response to one of a series of 

 stimuli 0.5 sec in duration repeated at 2-second intervals. Impulses occurring 

 before the onset of tlie stimulus were responses to a preceding stimulus. Intensity 

 of stimulus at 600 m^^ ^55 /tw/cm". See ref. (31) for relative intensities at other 

 wavelengths. 



particular unit illustrated in Fig. 5 had a very abrupt transition. The 

 response shifted from pure "on" to pure "off" with a wavelength 

 change of only 10 ni/x (Fig. 6) . 



Here indeed was a pattern of optic nerve discharge that seems to 

 follow the "C" responses. At short wavelengths, where the chromatic 

 response was large and negative, there was a vigorous "on" discharge 

 from the ganglion cell; as the wavelength was increased the number of 

 "on" impulses decreased just as the amplitude of the "C" response 

 decreased. AV^here the "C" response became zero there was a transi- 

 tion from "on" to "off." Where the amplitude of the depolarizing 

 phase of the"C" response was greatest the number of "off" responses 

 was also maximal. In some units (not illustrated) "on" and "off" 

 responses were both discharged at intermediate wavelengths, with a 

 decrease in the number of "on" responses and an increase in the num- 

 ber of "off" responses with increasing wavelength. The above com- 

 parison has as yet only been carried out qualitatively, because we 

 have not been able to study the "C" response in detail. 



In order to investigate the processes giving rise to the "on" and the 

 "off" response, the method of constant response was used. That is, 

 the stimulus was adjusted so that a constant response was obtained at 

 each wavelength rather than using a constant stimulus energy and 



