Figure 2.

Trial sequence for the c-f condition in experiment 1. Subjects fixated on the cross and pressed the space bar to initiate a trial. After 500 ms, the adapting curve appeared for 30 s in the first trial of a block (initial adaptation) and for 2 s (shown here) in all subsequent trials (top-up adaptation). After a 500 ms interstimulus interval (ISI), a test face appeared for 100 ms. The screen position of the adapting curve was identical to that of the mouth curves in the test faces. A beep was then played to remind the subjects to report the perceived expression of the test face. Subjects had to press either the “A” or the “S” key to indicate a perception of a happy or sad expression. Experimental parameters for all conditions and experiments are detailed in Materials and Methods.