Abstract
Decisions are made based on the subjective value that the brain assigns to options. However, subjective value is a mathematical construct that cannot be measured directly, but only inferred from choices. Is there another aspect of behavior that directly reflects subjective valuation of an option? Recent results have demonstrated that movement vigor is modulated by reward, raising the possibility that there is a link between how the brain evaluates an option, and how it controls movements toward that option. Alternatively, vigor may reflect salience and not value of the stimulus, growing larger for both stimuli that promise gain as well as stimuli that foretell loss. To dissociate between these possibilities, we asked people to choose among risky options represented by abstract stimuli, some associated with gain, others with loss. From their choices we estimated the subjective value that they assigned to each stimulus. In probe trials, they viewed only one stimulus at a time, and we measured their saccade vigor. We found that vigor was lowest for stimuli that promised loss, highest for stimuli that promised gain. This implied that vigor corresponded to value not salience. Naturally, a given stimulus was valued more by some participants. Remarkably, those who valued a given stimulus more tended to move with greater vigor in response to that stimulus. Thus, subjective value of a stimulus monotonically modulated the vigor with which the eyes moved to acquire a stimulus, suggesting that subjective valuation may be inferred from movement vigor.
Significance statement Does vigor of movements in response to an option reflect the subjective value that the brain has assigned to that option? If this were the case, vigor may provide an objective assay of subjective value, obviating the need to infer this variable from measurements of choice. Here, we show that saccade vigor varies monotonically with subjective value: smallest for stimuli that predict economic loss, and highest for stimuli that predict economic gain. Notably, between-subject differences in valuation may be gleaned from the between-subject differences in their patterns of vigor.
“A true theory of economy can only be attained by going back to the great springs of human action --- the feelings of pleasure and pain.” William Jevons (1866)