To investigate this hypothesis, Kennerley and colleagues (2006) used a discrete-trial version of the dynamic “matching” task, originally devised by Herrnstein (Herrnstein, Rachlin and Laibson, 1997) and used more recently by Sugrue and colleagues (Sugrue, Corrado and Newsome, 2004), which captures several of the key features faced by foraging animals described above. As in the previous joystick task, monkeys again are able to choose between one of two movements on each trial although now the contingencies never reverse throughout a testing session. However, there are two important differences to the joystick reversal task detailed in the previous section. First, rather than one of the two actions always being rewarded and the other non-rewarded, the likelihood of a response leading to a particular outcome was determined according to unequally assigned probabilities. Importantly, this allocation of rewards occurs independently for each option, meaning that on any particular trial, reward could be available regardless of which of the two actions the monkey chooses, only if it makes either a lift response or a turn response, or may not be forthcoming no matter what
