Emphasizing the “positive” in positive reinforcement: using nonbinary rewarding for training monkeys on cognitive tasks

Abstract

Nonhuman primates constitute an indispensable model system for studying higher brain functions at the neurophysiological level. Studies involving these animals elucidated the neuronal mechanisms of various cognitive and executive functions, such as visual attention, working memory, and decision-making. Positive reinforcement training (PRT) constitutes the gold standard for training animals on the cognitive tasks employed in these studies. In the laboratory, PRT is usually based on application of a liquid reward as the reinforcer to strengthen the desired behavior and absence of the reward if the animal's response is wrong. By trial and error, the monkey may adapt its behavior and successfully reduce the number of error trials, and eventually learn even very sophisticated tasks. However, progress and success of the training strongly depend on reasonable error rates. If errors get too frequent, they may cause a drop in the animal's motivation to cooperate or its adaptation to high error rates and poor overall performance. We introduce in this report an alternative training regime to minimize errors and base the critical information for learning on graded rewarding. For every new task rule, the feedback to the animal is provided by different amounts of reward to distinguish the desired, optimal behavior from less optimal behavior. We applied this regime in different situations during training of visual attention tasks and analyzed behavioral performance and reaction times to evaluate its effectiveness. For both simple and complex behaviors, graded rewarding was found to constitute a powerful technique allowing for effective training without trade-off in accessible task difficulty or task performance. NEW & NOTEWORTHY Laboratory training of monkeys usually builds on providing a fixed amount of reward for the desired behavior, and no reward otherwise. We present a nonbinary, graded reward schedule to emphasize the positive, desired behavior and to keep errors on a moderate level. Using data from typical training situations, we demonstrate that graded rewards help to effectively guide the animal by success rather than errors and provide a powerful new tool for positive reinforcement training.

Positive Reinforcement-Based Training for Self-Loading of Meat Horses Reduces Loading Time and Stress-Related Behavior

“…In sport horses, studies suggest that habituation to loading and traveling significantly reduces the likelihood that horses develop transport related behavioral problems and injury (16, 17). Loading training using positive reinforcement [consisting of reward delivery in response to the desired behavior (18)] also seems to reduce loading time and stress during loading (14, 19). Finally, it has been proven that self-loading techniques reduce the likelihood of horses showing behavioral problems (such as attempting to escape, rearing, kicking, pulling back, standing still, pawing) at loading (16, 17).…”

Using preferred fluids and different reward schedules to motivate rhesus macaques (Macaca mulatta) in cognitive tasks

“…In addition, recent work by Fischer and Wegener used a non-binary positive reinforcement approach. 28 They provided different volumes of fluid dependent on how optimally the monkey had performed a task (e.g. larger volumes for successfully performing a new step of the task and lower volumes for reverting to a previous version of the task).…”

Macaque monkeys learn and perform a non-match-to-goal task using an automated home cage training procedure

“…(b) The 19 steps presented during phase 1 of experiment 1. The monkey learns to touch a central stimulus (CS) of progressively smaller size (steps 1-5); to keep touching the CS while it is on the screen (steps 6-11); to remove its hand after the CS is turned off within a specific time window (steps 12-15), and to touch and continue toughing a target when it is presented on the screen (steps [16][17][18][19]. (c) The sequence of events of one trial of the non-match-to-goal task.…”

“…However, for this purpose, once training starts, they must be moved daily from their home cage to a special primate chair and carried to an experimental room where they perform the task. Even if protocols that allow monkeys to become accustomed to positive-reinforcement training can reduce the time spent by researchers in the initial stages of training 17,18 , the relocation procedure is nevertheless time-consuming and increases the risk of bites, scratches, and escape by the monkey. In recent years, increasing attention has been focused on the welfare of laboratory animals, and researchers constantly refine their methods to minimize the animals' stress and improve their well-being [19][20][21][22][23] , in accordance with the principles of the 3Rs (Replacement, Reduction, and Refinement) 24 .…”