Figure 1.

Experimental tasks. A, Trial structure for the multimodal reward task. Male, heterosexual young adults passively viewed a randomized sequence of images of female faces and monetary rewards (2 s event duration; 2 s fixation interval). The face images varied in valence from very attractive to very unattractive, based on ratings from an independent group of participants. The monetary rewards, whose value ranged from $5 to −$5, influenced the participant's overall payout from the experiment. To ensure task engagement, participants responded to infrequent visual targets that appeared as small yellow borders around the image. 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. Then a single face, randomly selected from the chosen attractiveness category, was displayed for 2 s. Trials were separated by a variable interval whose duration ranged from 2 to 6 s.