Figure 1.

Experimental design. A) An inert cream was applied to both feet while subjects were told that one particular foot was treated by lidocaine. B) During the conditioning blocks, low intensity laser pulses were delivered to the placebo foot while the control foot was stimulated by high intensity pulses. All trials contained a cue about the stimulus location. During the experimental blocks, both feet were stimulated by high intensity laser pulses and only half of the trials contained information about the stimulus location. C) At the beginning of the trial, a visual cue (informative vs non-informative) preceded the laser stimulus that had to be rated on a visual analog scale 3 seconds later.