Experimental procedure.

<p>The experiment was divided into two sessions. In one session short painful stimulation was applied over 2 sec while in the other session long painful stimulation was applied over 18sec while subjects had to perform a rapid serial visual presentation task (RSVP). In this task, subjects detected the target letter ‘A’ within a stream of letters presented in an individually calibrated presentation speed. Detection was indicated by pressing the left mouse button as fast as possible (detection task). In addition subjects were asked to memorize and indicate the appearance of the target letter ‘A’ (1, 2 or 3) presented within one trial using the numbers on the keyboard (counting task). Within the long pain session painful stimulation comprised five consecutive trials, while short painful stimulation comprised only one trial. Pain intensity ratings were obtained following every painful and non-painful control trial.