Figure 1.

Experimental design. A, Timeline of events within a trial. Events lasted 15–25 s with an average length of 20 s. Each event began with a 1 s vocal cue announcing either sweet or tasteless and a 2 s wait period, after which sucrose or tasteless solution was presented (0.5 ml over 3 s). Subjects were asked to indicate which solution they received by pressing a button on a button box as fast as they could during jitter 1 (various lengths that were randomized over trials). Then a 1 s swallow tone indicated that the subjects were allowed to swallow the liquid. After jitter 2 (various lengths that were randomized over trials), a new trial began. B, Graphical depiction of design. During training (left), all trials were valid (ExpSwt, validly cued sweet delivery; ExpTless, validly cued tasteless delivery). During the fMRI scanning, only 70% of the events were valid. The remaining 30% were invalid trials in which subjects heard tasteless but received sweet (UnSwt) or heard sweet and received tasteless (UnTless).