Figure 1.

Overview of task design. A, Chronological events and their duration in a trial during the taste psychophysics session. Each trial commenced with a taste delivery of.5 ml over 2 s. The participant was instructed to swallow immediately after receiving each liquid and then rate the intensity of taste. The intensity scale disappeared from the screen after ∼7 s or as soon as the rating was submitted by clicking a mouse button, whichever occurred first. Then a water rinse of 1 ml was presented over 4 s, followed by a rest period of 10 s before the next trial started, except after the tasteless stimulus, which was immediately followed by the next trial. B, The gLMS that was used for measuring perceived taste intensity. The specific taste quality to be rated (e.g., “sweetness” for sucrose and “saltiness” for sodium chloride) was indicated above the scale. When a participant received the tasteless solution the label was “overall intensity,” since no specific taste quality is associated with this stimulus. Participants used a scanner-compatible handheld trackball mouse to make ratings. The horizontal red cursor tracks up and down the scale with vertical mouse position, and clicking the left mouse button submitted the rating. A new gLMS then appeared on the screen to rate the next taste stimulus. C, Chronological events during a run in the fMRI session. Each block consisted of four, six, of eight repeats of a taste stimulus. Each repeat consists of a taste stimulus presentation over 2 s (0.5 ml), followed by a 7 s interval for swallowing. At the end of each block, a water rinse is presented over 4 s (1 ml), followed by a 15 s rest period before the start of the next block. Tasteless blocks are identical except that there is no water rinse before the 15 s rest period. Each run contained four taste blocks (one for each taste quality) and four tasteless blocks. No intensity ratings were made during the fMRI run.