Psychology, Department of


Date of this Version



Published in Behavioural Processes 71 (2006), pp. 29–40; doi: 10.1016/j.beproc.2005.09.003 Copyright © 2005 Elsevier B.V. Used by permission.


Animals show impulsiveness when they prefer a smaller more immediate option, even though a larger more delayed option produces a higher intake rate. This impulsive behavior has implications for several behavioral problems including social cooperation. This paper presents two experiments using captive blue jays (Cyanocitta cristata) that consider the effects of payoff accumulation and temporal clumping on impulsiveness and cooperation. Payoff accumulation refers to a situation where the benefits gained from each choice trial accumulate from one trial to the next, and only become available to the animal after it has completed a fixed number of trials. We hypothesized that this would reduce impulsiveness because it removes the advantage of quickly realizing food gains. Clumping refers to situation in which the animal experiences several choice trials in quick succession followed by a long pause before the next clump. We hypothesized that if payoffs accumulated over a clump of trials this would enhance the effect of accumulation. We tested the effects of accumulation and clumping on impulsiveness in a self-control situation. We found a significant interaction between clumping and accumulation. Payoff accumulation reduced impulsiveness, but only when trials were clumped. Post hoc analyses suggest that clumping alone increases impulsiveness. A second experiment applied these results to cooperation. This experiment reveals an interaction between payoff accumulation and trial’s position within the clump. Jays were more likely to cooperate on the first trial of a clump, but the likelihood of cooperation dropped after the first trial. However, this drop was larger when payoffs did not accumulate. This observation suggests that the difference between accumulated and unaccumulated treatments that we reported previously (Science 198: 2216–2218) may be largely due to differences in how animals behave in the first trial of a clump.