Figure 3.

Behavioral results for subjects in scanning experiment. A, Average quantity–bid functions show the difference in quality for three selected giftcards for subjects who completed both the behavioral and fMRI sessions (n = 25). B, In a prescanning paired-choice session, we confirmed that the ordering of cards by quality was highly consistent between sessions. C, Analysis of choices made in the MRI scanner. During the fMRI experiment, participants made 48 choices between cards of varying quality and quantity (Fig. 1D). We used the differences between options to predict choices using logistic regression. The differences between options in both quality (t₍₂₄₎ = 8.6, p < 0.001) and quantity (t₍₂₄₎ = 13.7, p < 0.001) were predictive of choice. Importantly, the interaction between quality and quantity also predicted choice (t₍₂₄₎ = 3.8, p < 0.001), consistent with the multiplicative relationship expected from the observed quantity–utility functions (A). Errors bars represent the SEM across subjects.