It has been reponted thnt nonirradinted monkeys associated peripherally placed stimuli with stimuli that were available for problem solving, and monkeys that had survived large doses of whole-body radiation with mixed source of radiation did not. This was interpreted as indicating that the response threshold of irradiated monkeys is displaced and their attention is narrowed. The present study was designed to determine whether the effect previously reported was related to changes in preferences of irradiated and nonirradiated monkeys for foods. Raisins and celery were selected as rewards, and it was hypothesized that a strong incentive (raisin) would cause the animals to attend to the problem at hand and ignore peripheral cues, whereas a weak incentive (celery) would favor the use of peripheral cues. Also, if groups differ in their preference for the incentives, this should be reflected in their ability to use peripheral cues. The test monkeys had survived three large doses of whole-body irradiation which were given 6, 7, and 8 yr earlier and totaled 1100 r. The results revealed three significant effects. One, which occurred with raisin rewards, was the tendency for irradiated monkeys to do less well on the second problem than on the first. This wasmore » the effect that had been reported under the same condition of reward. The effect was also significant during the second and third, but not during the first time the condition using raisins was presented. More striking was the effect produced by giving two different incentives. Every subject made a higher percentage of errors under celery than under raisin reward. Also, the effect disappeared under celery reward and there was a decline in errors between the first and second problems with celery rewards. Thus, the effect disappears under a weak incentive. This supponts the hypothesis that differences in food preferences of irradiated and nonirradiated monkeys explain the phenomenon of a narrowing of attention to stimuli. (BBB)« less