Sub-Optimal Choice Behaviour by Possums

Abstract

This study aimed to investigate sub-optimal choice using six brushtail possums (Trichosurus vulpecula.). Experiment 1 replicated Zentall and Stagner’s (2011) procedure where the possums were required to choose between two alternating alternatives; The low probability alternative (sub-optimal) was a discriminative stimuli signalling 3.5-s reinforcement on 20% of the trials, and non-reinforcement on 80% of the trials; the high probability alternative (optimal) was a non-discriminative stimuli signalling 1-s reinforcement 100% of the time regardless of the stimulus presented. This was unsuccessful as the possums showed a clear indifference to the alternatives. Due to these ambiguous results, we replicated two conditions of Stagner and Zentall’s (2010) procedures to achieve sub-optimal responding in possums. Experiment 2 was similar to Experiment 1, however the alternation was removed and the high probability alternative was a non-discriminative stimuli associated with 50% reinforcement regardless of the stimulus presented. Sub-optimal responding was not achieved, however the possums now showed a preference for the optimal alternative. Alternation may have affected Experiment 1 and to examine this theory, Experiment 3 was replicated without alternation. Interestingly, we found a preference for the high probability alternative. Experiment 4 replicated Experiment 3; however the length of time for reinforcement was altered to attenuate sub-optimal responding. A preference for the high probability alternative which provided an overall greater net payoff was found. The possums changed from indifference to choosing optimally. It appears that possums do not have a preference for the sub-optimal choice the same as pigeons.