732 



W. LYNN BROWN AND ARNOLD A. McDOWELL 



0-6ROUP I -INTERVENING DARKNESS 

 • -6R0UP II -REGULAR ILLUMINATION 



4C- 



Z 30- 



uj 20- 



FiG. 2. Facilitated spatial delayed response performance of monkeys tested on 

 discriminative, but ambivalent, cue delay problems with darkness during the delay. 



Fig. 3. Per cent errors per group per day on the spatial delayed response problem. 



subjects could and did perform as efficiently at some points in time as the 

 chronic irradiated subjects, but they appeared to suffer interference from 

 extraneous stimuli. 



Figure 4 shows the results of a study conducted by McDowell and Brown 

 (1958) to test the prediction of facilitated performance by the same irradi- 

 ated subjects on discrimination problems with reduced stimulus cues. This 

 task, developed by Cowles and Nissen (1937), combines aspects of object 

 discrimination and delayed response. In the Wisconsin General Test Ap- 

 paratus (WGTA), two identical cues are placed over the food wells. During 

 the learning trial of each problem, a discriminable cue rests on top of that 



