734 W. LYNN BROWN AND ARNOLD A. McDOWELL 



recently occupied by the positive training stimulus was chosen by the control 

 and the low dose irradiated subjects to a significant degree. The high dose 

 irradiated subjects manifested no preference for that position associated 

 with reward on the most recent training trial. The results were interpreted 

 as indicative of a narrowed scope of attention in the high dose irradiated 

 subjects. 



Brown et al. (1958a) hypothesized that, if irradiation results in decreased 

 distractibility with a consequent narrowing of attention, the irradiated 

 subjects should prove less efficient than normal subjects in association of 

 peripheral cues. In the test of their hypothesis, stimuli which were periph- 

 eral on the initial problem became focal on the second problem. The 

 results supported the tenability of their hypothesis. The controls evidenced 

 association of peripheral cues, while irradiated subjects did not. 



Gentry et al. (1958) trained the same subjects on intermediate-size 

 discrimination problems. A test of transposition was then employed to 

 determine the extent to which subjects of the diflferent subgroups utilized 

 relationships between stimuli as a basis for problem solution. Relational 

 learning was found to decrease as a linear function of radiation dosage. 

 The investigators did not interpret the results as suggesting a decrement 

 for the irradiated animal with respect to relational learning. They, rather, 

 interpreted the results as suggesting that, if given a choice, the irradiated 

 animal will utilize learning in teiTns of absolute stimulus properties, rather 

 than learning in terms of relations. 



McDowell and Brown (1960a) studied these same subjects under condi- 

 tions of repetitious work. Each subject was given 50 trials (or until balking 

 occurred) each day for 44 days on a single form-discrimination problem. 

 If any subject refused to respond within 3 minutes at any point in the daily 

 testing, he was accorded a balk and testing was discontinued. A significantly 

 larger proportion of controls than of irradiated subjects manifested balks, 

 and the balking controls showed significantly more balks. The number of 

 trials worked during successive 4-day periods varied significantly over time 

 for the balking controls. 



These findings were considered by the authors to support an hypothesis 

 of greater work decrement for normal than for previously irradiated monkeys 

 under conditions of repetitious work. The results suggest response compe- 

 tition for the normal subjects between the relevant stimuli of the test 

 situation and extraneous stimuli. 



Another study was conducted by McDowell and Brown (1960d) to com- 

 pare the response perseveration of some of the same irradiated subjects 

 with that of normal subjects when tested according to the proactive inhi- 

 bition paradigm. The study specifically involved the effects of initial training 

 on a peripheral cue discrimination problem, during which no learning was 



