The Pavlovian autoshaping paradigm has often been used to assess the behavioral effects of reward omission on behavior. We trained pigeons to receive a food reward (unconditioned stimulus, or UCS) following illumination of a response key (conditioned stimulus, or CS). In Experiment 1, 1 group of pigeons was trained with two 100% predictive CS-UCS associations (reward certainty) and another group with two 25% predictive CS-UCS associations (reward uncertainty) for 12 sessions. In both groups, the 2 CS durations were 8 s. Then, in each group, the duration of 1 CS remained unchanged and that of the other CS was suddenly extended from 8 to 24 s for 6 sessions. In Experiment 2, some experienced individuals (from Experiment 1) and naïve individuals formed 2 groups trained with a 24-s CS throughout for 18 sessions. Our results show that pigeons (a) pecked less at the uncertain than the certain CS, (b) decreased and then increased CS-pecking after extending the CS duration, especially in the certainty condition, (c) were unresponsive to the 24-s CS in the absence of previous experience, and (d) decreased their response rate close to the end of a trial irrespective of the reinforcement condition, CS duration, and amount of training. These results are discussed in relation to several theoretical frameworks.

Wittek, N., Wittek, K., Güntürkün, O. & Anselme, P. (2021). Decreased key pecking in response to reward uncertainty and surprising delay extension in pigeons. International Journal of Comparative Psychology, 34, 1-17.