DETERMINANTS OF PIGEONS CHOICE BETWEEN CERTAIN AND PROBABILISTIC OUTCOMES

Pigeons chose between 50% and 100% reinforcement on a discrete-trials concurrent-chains procedure with fixed-ratio 1 initial links and fixed -time terminal links. The 100% alternative always provided food after a terminal-link delay, whereas the 50% alternative provided food or bl ackout equally often after a delay. Additionally, the terminal-link st imuli on the 50% alternative were correlated with the outcomes in sign aled, but not in unsignaled, conditions. The effects of intertrial-int erval duration and length of the terminal-link delays on choice of the 50% alternative were investigated in four experiments. Preference for the 50% alternative varied with signal condition and duration of the terminal link leading to food, but not with duration of either intertr ial interval or the terminal link leading to a blackout. The results a re discussed in terms of conditioned-reinforcement effects, Mazur's hy perbolic-decay model, and delay reduction.