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ARTHUR J. RIOPELLE 



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Fig. 3. Performance of normal and irradiated chimpanzees on a task in which they 

 had to select the unique stimulus from three identical stimuli. 



patterns appeared only once. New stimulus combinations were constructed 

 each day by re-pairing the supply of 200 triplicate sets of plaques. Figure 3 

 provides no room for doubt as to the inferiority of the irradiated animals. 



The two particular tests described were administered from 3 to 5 years 

 after irradiation, long after the animals had recovered from the acute effects 

 of irradiation. As is well known, radiation sickness produces anorexia, lassi- 

 tude, and inactivity. When the animals of the present study were afflicted 

 with radiation sickness, they frequently refused to attempt the tests. On other 

 days their responses slowed considerably. Measures based on speed of re- 

 sponding, if they deteriorated, did so during radiation sickness (Table II). 

 After they recovered from this phase, the animals' motivation was restored, 

 and they never failed to respond in the test situation. Also, their activity 

 returned to preirradiation levels. 



In summary, irradiation of chimpanzees with 375-400 r of gamma radia- 

 tion over 12 hours, produced few permanent behavioral losses. On a few 

 tests, conducted several years after treatment, the irradiated animals were 

 significantly inferior to the normals in accuracy of response. Whether this 

 should be attributed to the irradiation, to characteristics of this particular 

 small sample, or to pure chance, is not answerable. Despite the obvious 

 importance of any signs of deficit for treatment of humans, we would wish 

 to be cautious in concluding that 375-400 r will produce permanent inca- 

 pacitation of an intellectual of perceptual nature. One reason for remaining 

 cautious is that some of the tests which produced loss in this study did not 

 do so in other laboratories or in monkeys (Riopelle et al., 1956; Harlow and 



