Effects of reward expectancy on sequential eye movements in monkeys

Desirability of an action, often referred to as utility or value, is determined by various factors, such as the probability and timing of expected reward. We investigated how performance of monkeys in an oculomotor serial reaction time task is influenced by multiple motivational factors. The animals produced a series of visually-guided eye movements, while the sequence of target locations and the location of the rewarded target were systematically manipulated. The results show that error rates as well as saccade latencies were consistently influenced by the number of remaining movements necessary to obtain a reward. In addition, when the animal produced multiple saccades before fixating a given target, the first saccade tended to be directed towards the rewarded location, suggesting that saccades to rewarded location and visual target might be programmed concurrently. These results show that monkeys can utilize information about the required sequence of movements to update their subjective values.