802 



LIGHT AND LIFE 



Fig. 4. Typical "on-off" response from retinal ganglion cell. The stimulus was 

 0.6 sec duration, 700 m^ wavelength, 0.7 fi^s/cm" intensity, 2 mm in diameter. In 

 this and in subsequent records, the presence of the stimulus is indicated by a step 

 in the signal trace at the base of the record. 



in the frog retina. Indeed, it i.s characteristic of all types of verte- 

 brate retinas (8, 9, 10, 14). However, some units were found that 

 gave a prolonged discharge during illumination, and a few which 

 were spontaneously active in the dark were inhibited by light. 



Thus far only the "on-off" units have been studied extensively. 

 Many of these gave a response that was dependent upon wavelength 

 in a very unusual way. If a series of flashes having a duration of 0.5 

 sec or so were j^resented at regular intervals of a second or two, the 

 "on-off" pattern showed wavelength dependency. This is well illus- 

 trated in Fig. 5, where a typical element gave piue "on" responses 

 in the short-wave end of the spectnun and jiure "off" resjionscs in 

 the long-wave end. The change from "on" to "off" occurred at an 

 intermediate wavelength. Granit (11) has reported changes in the 

 off/on ratio of the responses of retinal ganglion cells of the cat, 

 which suggest that a similar mechanism may be present to some extent 

 in this animal. DeValois (7) , recording from ganglion cells of the 

 lateral genicidate of the monkey, also observed that a change in wave- 

 length could convert an "on" response into an "off" response. The 



