Figure 1.

Experimental task. (A) Trial structure of the Incentive Delay Task. Male, heterosexual young adults viewed a cue (0.5 s) predictive of reward type and magnitude. Monetary rewards (left panel) ranged from $1 to $10. A monetary reward control predicted $0. Social rewards (right panel) ranged from 1-star (unattractive) to 5-stars (very attractive), based on ratings from an independent group of participants. A social reward control condition predicted the picture of a scrambled face. After a variable delay (2–2.7 s) a visual target (white square) appeared (<0.5 s). Participants were instructed to respond as quickly as possible to the visual target. After the response, an outcome screen (1.5 s) revealed their reward: money or picture of a face if the response was fast enough, or no money or the picture of a scrambled face if the response was too slow. Reaction time thresholds were defined for each subject and each cue independently in a practice run that preceded the task, such that on average participants succeeded in 60% of the trials. (B) Trial structure for the economic exchange task. Trials began with a decision phase (lasting 4 s) in which the participant was forced to spend a small amount of money to view a face. Participants could choose to spend more money to view a more attractive face or less money to view a less attractive face. Following the decision phase, there was an anticipation phase that lasted either 2 or 4 s. A single face, randomly selected from the chosen attractiveness category, was then displayed for 2 s. Trials were separated by a variable interval of 2–6 s.