652 SYLVAN J. KAPLAN 



hind legs. All older animals that were run beyond 25 trials failed to eat in 

 the goal box on completion of the trial. No such behavior was seen in any 

 of the rats in the 90 day groups. 



Experiment Two 



To ascertain if a behavioral deficit may be determined by a learning 

 instrument other than the maze, an operant conditioning task was made a 

 part of the test battery given the subjects. Melching (1956-1957) previously 

 found in a pilot study an indication that prenatally irradiated subjects show 

 some impairment in capacity to condition and extinguish a bar pressing 

 habit. Since this represents perhaps a simpler and certainly a different type 

 of learning requirement than that of maze learning, it was felt that the 

 differences noted in experiment one might be confirmed and elaborated. 



Procedure 



The apparatus used was the Model DB-103 demonstration Skinner box 

 (Davis Scientific Instruments, Studio City, California) with Model BM-105 

 bar mechanism, Model PD-104 pellet dispenser, and Model CB-106 control 

 box and power supply. Automatic recording of the animals' responses was 

 accomplished by the Davis Model CRRC-133 cumulative recorder, the 

 Model 1704 counter, and Model 1721 print-out counter (Foringer, Rock- 

 ville, Maryland). Food pellets weighed 45 mg (P. J. Noyes Co., Lancaster, 

 New Hampshire). 



Testing was conducted on 3 consecutive days. On day 1, each subject 

 was placed in the apparatus to precondition for 30 minutes, and its pre- 

 operant level of responding was determined. During this time, the pellet 

 dispenser was allowed to operate with each bar pressing response, but no 

 food was delivered into the apparatus for reinforcement of responses. On 

 day 2, the subject was placed in the apparatus for 60 minutes of condition- 

 ing, and each response was reinforced by one pellet of food. On day 3, the 

 subject was returned to the apparatus and allowed to remain until extinction 

 of the bar pressing responses had occurred. As on day 1, the pellet dispenser 

 operated with each response, but the pellets were withheld from the animal 

 by being allowed to fall outside the test box. Extinction was defined as 

 occurring when the number of responses during any 30 minute period fell 

 to or below the number of responses recorded during the 30 minute pre- 

 conditioning on day 1. 



Each subject was placed on a total food deprivation schedule 24 hours 

 before starting the tests. No food, other than that obtained by the bar 

 pressing on day 2, was furnished during the experiment. Thus, each had 



