Basing higher-order decisions on expected value (reward probability Ï« reward magnitude) maximizes an agent's accruement of reward over time. The goal of this study was to determine whether the advanced preparation of simple actions reflected the expected value of the potential outcomes. Human subjects were required to direct a saccadic eye movement to a visual target that was presented either to the left or right of a central fixation point on each trial. Expected value was manipulated by adjusting the probability of presenting each target and their associated magnitude of monetary reward across 15 blocks of trials. We found that saccadic reaction times (SRTs) were negatively correlated to the relative expected value of the targets. Occasionally, an irrelevant visual distractor was presented before the target to probe the spatial allocation of saccadic preparation. Distractor-directed errors (oculomotor captures) varied as a function of the relative expected value of, and the distance of distractors from, the potential valued targets. SRTs and oculomotor captures were better correlated to the relative expected value of actions than to reward probability, reward magnitude, or overall motivation. Together, our results suggest that the level and spatial distribution of competitive dynamic neural fields representing saccadic preparation reflect the relative expected value of the potential actions.Key words: motor planning; reaction time; reward; probability; motivation; dynamic field theory
IntroductionThe generation of saccadic eye movements is influenced by bottom-up factors such as the contrast and luminance of visual stimuli as well as top-down factors such as goals, expectations, and context (Thompson and Bichot, 2005;Fecteau and Munoz, 2006). Of these, top-down factors are more difficult to define, quantify, and manipulate in the laboratory, and consequently, their influence is less understood (Sparks, 1999;Maunsell, 2004;Schall, 2004). Here, we manipulated a set of variables that were easily defined and quantified to better understand how top-down factors influence the advanced allocation of saccadic preparation.Expected value (defined as the product of the probability of reward for an action and the magnitude of that reward) is a critical factor when making any decision, because choosing the option with the highest expected value maximizes the intake of reward over time. Behavioral and neurophysiological studies linking each of these individual components of expected value to changes in saccadic generation have recently been described. For example, experiments describing probability effects involved probability manipulations while reward magnitude remained constant (Basso and Wurtz, 1998;Dorris and Munoz, 1998;Platt and Glimcher, 1999). Similarly, experiments describing reward magnitude effects involved magnitude manipulations while probability remained constant (Leon and Shadlen, 1999;Platt and Glimcher, 1999;Lauwereyns et al., 2002;Takikawa et al., 2002;Ding and Hikosaka, 2006). Therefore, attributing chan...