Fig. 2.

Steps to complete a trial of the training task with choice stimuli present. Monkeys touched the green ready square to initiate trials. Choice and test images then appeared on screen: the target circle of constant size, three distracters identical to one another, and the accept-test and decline-test choice stimuli. On 1/3 of trials (right), the decline-test response did not appear. Choice of the accept-test stimulus extinguished choice stimuli and activated test stimuli. Tests resulted in food reinforcement of two pellets (correct) or a black time out screen (incorrect). Selection of the decline-test response caused the guaranteed small reward stimulus screen to appear. Touches to this stimulus resulted in guaranteed food reinforcement of one pellet