Vol.:(0123456789) 1 3 Animal Cognition https://doi.org/10.1007/s10071-020-01352-9 ORIGINAL PAPER Pigeons can learn a difcult discrimination if reinforcement is delayed following choice Dalton House 1  · Daniel Peng 1  · Thomas R. Zentall 1 Received: 25 November 2019 / Revised: 15 January 2020 / Accepted: 20 January 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Delaying reinforcement typically has been thought to retard the rate of acquisition of an association, but there is evidence that it may facilitate acquisition of some difcult simultaneous discriminations. After describing several cases in which delaying reinforcement can facilitate acquisition, we suggest that under conditions in which the magnitude of reinforcement is dif- fcult to discriminate, the introduction of a delay between choice and reinforcement can facilitate the discrimination. In the present experiment, we tested the hypothesis that the discrimination between one pellet of food for choice of one alternative and two pellets of food for choice of another may be a difcult discrimination when choice consists of a single peck. If a 10-s delay occurs between choice and reinforcement, however, the discrimination is signifcantly easier. It is suggested that when discrimination between the outcomes of a choice is difcult and impulsive choice leads to immediate reinforcement, acquisition may be retarded. Under these conditions, the introduction of a brief delay may facilitate acquisition. Keywords Discrimination · Magnitude of reinforcement · Delay of reinforcement · Pigeons Introduction The subjective value of reinforcement depends in part on the delay to reinforcement (Hull 1943). Typically, the longer the delay, the lesser the value. The efect of delay of reinforce- ment can be seen in the delay discounting efect in which a smaller reinforcer sooner may be preferred over a larger reinforcer later (Ainslie 1974). The delay discounting func- tion describes the degree to which an organism will wait for the larger delayed reinforcement as the delay increases. The slope of the delay discounting function (refecting how little time must pass before the organism switches from the larger later reinforcer to the smaller sooner reinforcer) refects the impulsivity of the organism or its lack of self-control. In a classic paper, Rachlin and Green (1972; see also Kurth-Nelson and Redish 2012) found that pigeons would choose the larger later more often if they would make a prior “commitment”. To accomplish this, at a time before the choice of smaller sooner versus larger later, the pigeons were allowed to choose between having a delayed choice and being forced to take the larger later without a choice. Interestingly, the pigeons preferred choosing not to have a later choice. One could describe this initial choice as not being “tempted” later to make the smaller sooner choice. Although this choice not to choose may seem paradoxical, it actually is predicted from the efect of the delay, in delay discounting research. If other variables are held constant, the preference between two intervals will depend on the ratio of the two intervals. For example, if the delay to the smaller sooner is 1 s and the delay to the larger later is 10 s, then the ratio of the two would be 1:10, a ratio that strongly favors the sooner reinforcement. On the other hand, if the initial choice is made 10 s earlier, then the ratio of the two would be 11:20 or about 1:2, a ratio that may be overcome by the delayed larger reinforcer. The idea that the temporal diference between two reinforcers can be reduced subjectively by increasing the delay to both reinforcers is well understood but what if the diference in the magnitude of reinforcement is not so great (2:1 rather than 4:1) such that the discrimination between them is dif- fcult and the temporal diference between two reinforcers is small or nonexistent? Under these conditions, the efect of a joint delay of reinforcement of the choice response for both alternatives is not so clear. It is also possible that by inserting a delay between smaller reinforcer sooner it * Thomas R. Zentall zentall@uky.edu 1 Department of Psychology, University of Kentucky, Lexington, KY 40506, USA