EFFECTS OF RADIATION ON PSYCHOLOGIC PROCESSES 745 



the major groups discussed is worthy of note. Studies by Brown et al. 

 (1958b) on conceptual discrimination, by Brown ct al. (1959) on novelty 

 learning set, by McDowell and Brown (1960c) on peripheral cue learning 

 set, and by McDowell and Brown (1961a) on approach-avoidance learning 

 set have yielded negative results with respect to the radiation variable. One 

 might speculate that the frequent introduction of novel test stimuli in prob- 

 lems of this type keeps the attention of the controls focused on the problem 

 and, in consequence, militates against radiation differences. 



The procedure in the conceptual discrimination research is illustrative of 

 the recurrent novelty factor. In one experiment, object-quality discrimination 

 problems were presented in a series in which the positive (rewarded) stim- 

 ulus object on any given problem (after the first) was the negative 

 (unrewarded) stimulus of the preceding problem. In a second experiment, 

 the negative (unrewarded) stimulus object of each successive problem was 

 the positive (rewarded) object of the preceding problem. Since each problem 

 was presented for only fom- trials, a novel stimulus object was presented 

 on every fifth trial. It was also the case on each of the other concept 

 fonnation studies that no\el stimuli were introduced on every fifth trial. 



In summary, radiation for both field and laboratory exposed rhesus 

 monkeys produces decreased distractibility or, in other words, increased 

 concentration of attention. The general resultant for learning is facilitation 

 of performance on tasks placing a premium on attention to the site of food 

 reward and decrement in performance on tasks requiring attention to 

 peripherally placed stimuli. Whether test results of this nature reflect direct 

 or indirect effects of radiation exposure on the central nervous system 

 remains to be solved. 



References 



Brown, W. L., and McDowell. A. A. 1960. Visual acuity performance of normal and 



chronic irradiated monkeys. /. Genet. Psychol. 96, 133-137. 

 Brown, W. L., Carr, R. M., and Overall, J. E. 1958a. The Effects of Whole-Body 



Irradiation upon Association of Peripheral Cues U. S. Air Force School of Aviation 



Med. Report No. 57. 

 Brown, W. L., Overall, J. E., and Gentry, G. V. 1958b. Conceptual discrimination in 



rhesus monkeys. /. Comp and Physiol. Psychol. 6, 701-705. 

 Brown, W. L., Overall, J. E., and Blodgett, H. C. 1959. Novelty learning sets in 



rhesus monkeys. /. Comp. and Physiol. Psychol. 3, 330-332. 

 Cowles, A. T., and Nissen, H. W. 1937. Reward expectancy in delayed response of 



chimpanzees. /. Comp. Psychol. 24, 345-358. 

 Davis, R. T., Elam, C. B. and McDowell, A. A. 1957. Latent Effects of Chronic 



Whole-Body Irradiation of Monkeys with Mixed Source Radiation. U. S. Air 



Force School of Aviation Med. Report No. 59. 

 Gentr>-, G. V., Brown, W. L., and Overall, J. E. 1958. The Effects of Ionizing Radia- 



