Investigating the effects of olfactory stimuli on rats' choices for probabilistic reinforcers

Animals typically prefer choice alternatives that deliver food with a higher probability. However, previous research has shown that some animals will choose a lower probability alternative when it contains a signal about when food will be delivered, a phenomenon sometimes called suboptimal choice. Although this finding has been repeatedly demonstrated in pigeons, results with rats have been mixed, indicating that the stimulus modality may influence choice. In the current study, female rats' choices for delayed and probabilistic food were examined using a concurrent-chains procedure, with olfactory terminal-link stimuli. In Experiment 1, four of six rats preferred the lower probability alternative. In Experiments 2 and 3, a statistically significant group-level preference for the lower probability alternative was observed, despite increasing the number of free-choice trials in a session and reversing the location of the choice options. Data on the number of pellets rats earned across the three experiments were tracked to quantify how rats' proportion choice of the lower probability alternative affected the number of pellets earned during each session, providing insight into how much food rats are willing to forego for a choice alternative with a predictive stimulus.