Figure 1.

Schematic overview of the experimental task during the practice, acquisition, and generalization phases. The eight equally spaced movement quadrants that served as CSs (1 and 8) and GSs (2–7) were delineated by white borders during the practice phase (upper panel). In the predictable group, the CSs and GSs are referred to as CS_p+, CS_p−, and GS_p1–GS_p6; these stimuli are referred to as CS_u1, CS_u2, GS_u1–GS_u6 in the unpredictable group. Participants had to move the joystick in the area that colored green and had to aim toward the yellow border. At the end of each of these movement areas a blue bar was positioned; the corresponding blue bar turned yellow when a movement was successfully performed. During the acquisition phase (middle panel), participants only carried out two movements (CSs). After “+” was presented in the middle of the screen, this was replaced by a number that indicated the movement direction (1 or 8). In the predictable group one of these movements was followed by a pain-US (CS_p+, i.e., left) indicated by a lightning bolt, whereas the other movement (CS_p−, i.e., right) was never followed by the pain-US. In the unpredictable group, movements (CS_u1/CS_u2) were never followed by the pain-US, but it was delivered during the ITI. Finally, during the generalization phase (lower panel) participants had to perform all movements (GSs and CSs) under extinction (i.e., none of the movements were followed by the pain-US).