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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 34, 2021

Research Article

Decreased Key Pecking in Response to Reward Uncertainty Followed by Surprising Delay Extension in Pigeons

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, one 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 two CS durations were 8 s. Then, in each group, the duration of one 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 two 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 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.

Brief Report

Understanding and assessing emotions in marine mammals under professional care

In the last 30 years, concerns about animal emotions have emerged from the general public but also from animal professionals and scientists. Animals are now considered as sentient beings, capable of experiencing emotions such as fear or pleasure. Understanding animals’ emotions is complex and important if we want to guarantee them the best care, management, and welfare. The main objectives of the paper are, first, to give a brief overview of various and contemporary assessments of emotions in animals, then to focus on particular zoo animals, that is, marine mammals, since they have drawn a lot of attention lately in regards of their life under professional care. We discuss here 1 approach to monitor their emotions by examining their laterality to finally conclude the importance of understanding animal emotion from a holistic welfare approach.