Fig 1. Positive reinforcement training.

A) Acclimation to syringe for juice training. Male rhesus macaques (n = 7) were enrolled in a PRT program which used sweet liquids administered from a 60-cc catheter tip syringe as a reinforcer. Syringe acclimation was done over a period of three weeks, with training five days a week. Liquids tested included fruit juices (mango, apple, cranberry, passion fruit, pomegranate, and peach), diluted strawberry syrup, diluted molasses, vanilla ensure, kefir, yogurt and chocolate milk. Each individual animal is represented by a distinct shape/fill. B) Daily positive reinforcement training (PRT) time. Animal and trainer interactions were timed during training sessions with a stopwatch. Times when the animals did not successfully complete any desired behavior are included. Data shows results obtained over a two-month period when animals were trained to shift location in their cage, sit and accept liquid from a syringe. Individual daily training times are represented by circles; bars denote mean ± SEM.