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. 2018 Oct 22;3(6):e694. doi: 10.1097/PR9.0000000000000694

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Copyright © 2018 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of The International Association for the Study of Pain.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

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Figure 1. — Structure of the experiment: (A) The experiment consisted of 4 blocks with 8 stimulation trials each. In half of the cases, the stimulation could be stopped by the participant (controllable condition). The remaining trials were stopped by the computer (uncontrollable condition). The duration of the self-controlled trials equaled the duration of the computer-controlled trials in the subsequent block (dotted arrows). The order of the trials was randomized within each block. (B) Each trial was announced by a slide that indicated the type of the trial. Note that in 25 participants, the word “self” was replaced by the word “button press” to announce the controllable trials. The anticipation phase was followed by a varying interval of painful stimulation, ratings of pain intensity, pain unpleasantness, and pain-related suffering. Each trial ended with an off-block lasting 12 seconds. ISI, interstimulus interval.