Figure 3.

Psychometric analysis of individual subject data. Data from the scanning session are shown for two exemplar subjects (a, b). For each subject, the top row shows the probability of acceptance, and the bottom row shows reaction times (RTs), both plotted against offer proportion (each data point being the mean of 5 trials). Data are shown for the M offers in the three contexts: M-alone (green; neutral), M-in-L (blue; more fair), and M-in-H (red; less fair). The top row also shows probability of acceptance as a logistic function fitted to those points, demonstrating a contextual bias evident in a shift to the left for contextually more fair (M-in-L) and a shift to the right for the less fair (M-in-H) relative to the control condition (M-alone). In the bottom row, it can be seen that the point of indifference (probability of acceptance is 0.5) corresponds to peak reaction times, consistent with choice difficulty being greatest at this point and arguing against either acceptance or rejection as being a “default” choice.