Four groups of pigeons were trained to perform a delayed matching-to-sample task with a single delay of 0, 2, 4, or 6 s from the outset of training. The longer the training delay, the more sessions were required for all birds to reach the same level of response accuracy. Following initial training, five test sessions that included nonreinforced trials with delay intervals of 0, 2, 4, 6, 8, and 10 s were interspersed between training sessions. Unlike typical forgetting functions in which accuracy decreases monotonically with increasing delay, the forgetting functions from test sessions resembled generalization gradients with the peak of the functions occurring at the training delay. Following additional training for all birds with a 0-s delay, forgetting functions decreased monotonically with increasing delay. The results suggested that remembering can be trained at a specific delay interval, and generalizes to similar delay intervals. Generalization along the temporal dimension of delay may contribute to typical forgetting functions in which accuracy decreases from 0-s delay.

A magnitude effect in human intertemporal choice is well established-larger rewards or outcomes are discounted over time at a lower rate than are smaller rewards. However, many recent studies have failed to find a corresponding effect in nonhuman animals. Here we report a magnitude effect in temporal discounting for pigeons' choices involving a tradeoff between reward delay and amount. Pigeons chose between a small reward (1-s access to food) after a 2-s delay, and a large reward (4.5-s access to food) after a 28-s delay. Across conditions, the delays to the small and large rewards were increased or decreased, respectively. Temporal discounting functions obtained through a value-estimation procedure showed clear evidence of a magnitude effect: The value of the large reward decreased more slowly with increasing delay than the value of the small reward. We linked this result to a nonlinear relationship between choice and the delays associated with the small and large rewards. The nonlinearity was contrary to the generalized matching law but was predicted by the contextual choice model. Our results confirm the existence of a magnitude effect in nonhuman temporal discounting, showing that this adaptation is not unique to humans.

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Pigeons were trained in a matching-to-sample procedure with retention intervals of 0, 2, 4, 6, and 8 s mixed within each session. In different conditions, reinforcement was delayed by 0, 1, 2, 4, 6, or 8 s from correct choice responses. Discriminability decreased with increasing retention-interval duration and with increasing reinforcer delay. Exponential forgetting functions were fitted to discriminability measures plotted as a function of retention interval. Initial discriminability (intercept of the fitted functions) decreased with increasing reinforcer delay. Rate of forgetting (slope of the fitted functions) increased with reinforcer delay, suggesting an interaction between the effects of reinforcer delay and retention interval. The data were well described by multiplying an exponential function describing the effects of retention interval by a hyperbolic function describing the effect of reinforcer delay. This description included an interaction term that allowed for a greater effect of reinforcer delay at longer retention intervals.

Policymakers may be reluctant to implement pro-environmental policies that the public find unacceptable, such as policies intended to reduce car use. It is, therefore, essential to understand factors that influence acceptability of such measures. We aimed to study to what extent policy acceptability of car-reduction policies is related to personal norms to do the ''right thing" and perceived costs associated with the policies. We hypothesized, in line with the A-B-C model, that personal norms would be more strongly related to policy acceptability when the policy was associated with moderate personal costs, rather than with very low or high costs. Such a finding would be somewhat contrary to the low-cost hypothesis, which predicts a simple linear relationship between costs and personal norm, such that personal norms become better predictors of acceptability as costs decrease. We tested this hypothesis in two ways, using data from 6045 people from seven European countries. First, we hypothesised and found that personal norms were less predictive of the acceptability of a pull measure involving few external costs (improved provision of public transport) than of a push measure involving a higher degree of cost (increased car-use taxes), across all countries. Second, we hypothesised and found that, overall, personal norms were more predictive of acceptability of the push measure when respondents felt more able to reduce their car use, and thus when the push measure would be associated with lower personal costs. This result was stronger for some countries than for others. We discuss implications for policy.