680 WILLIAM J. ARNOLD 



Discrimination Learning Based on Visual Exploratory Drive 



This experiment was designed to test discrimination learning motivated 

 by visual exploratory drive. It was thought that discrimination learning 

 might be a more sensitive indicant of differential drive strength than the 

 latency measure. 



Of 14 rats 280 days old and previously tested for maze learning, 7 were 

 irradiated and 7 served as controls. Irradiation was carried out 190 days 

 before the start of the experiment. The apparatus was essentially the same as 

 that used in the visual exploration experiments. It consisted of a box with 

 two windows covered by doors which the rat could push open. Black or white 

 cards were attached to these doors and, in order to respond correctly, the 

 rat was required to discriminate between these cards. Errors (pushes on the 

 incorrect or locked door) were electrically recorded. 



After preliminary training, the animals were given 50 discrimination 

 training trials at the rate of 10 trials per day. The criterion of learning was 

 32 correct responses out of 50. Animals achieving this criterion can be said 

 to have learned the discrimination at the 5% level of significance. 



Results 



One experimental and one control animal failed to adapt to the situation 

 and were discarded during preliminary training. One of the irradiated rats 

 died during discrimination training. Four of the remaining six control ani- 

 mals and three of the remaining five irradiated animals learned the discrimi- 

 nation. This difference is not statistically significant. Thus, it appears that 

 irradiation did not significantly affect discrimination learning motivated by 

 visual exploration. 



Summary and Conclusions 



These investigations show that, in rats, sufficiently large doses of cranial 

 irradiation produce symptoms of radiation sickness similar to those for total 

 body irradiation. These symptoms are not produced by equivalent amounts 

 of irradiation to another part of the body, such as the hind leg. 



Either directly or indirectly (via the production of radiation sickness), 

 cranial irradiation seems to affect some behavioral processes but not others. 

 At least two parameters are important in testing any of the behavioral proc- 

 esses: dose size and the time interval after irradiation. Most of the work 

 reported here involved doses of 2,500 r to the whole head and 5,000 r to 



