Expectancy and task incentive effects on pain and somatic focus.

<p>A. <b>Mediation Model Results:</b> There were main effects of: 1) Expectancy Cue (high vs. low) on Somatic Focus (Path <i>a</i>); 2) Somatic Focus on pain ratings (Path <i>b</i>); 3) Expectancy cue on pain ratings (Path <i>c</i>); 4) Task-Incentive Cue on Somatic Focus (Path <i>d)</i>; and 5) Task-Incentive cue on pain ratings (Path <i>e</i>) (see below for details of main effects; full statistics are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038854#pone-0038854-t001" target="_blank">Table 1</a>). Expectancy effects on pain reports were mediated by changes in somatic focus (<i>c – c’</i>) with a negative mediation effect, indicating that increases in somatic focus partially suppressed the pain-intensifying effects of high pain expectancy (p<0.05). The effect of Task-Incentive cue on pain was mediated by changes in somatic focus (<i>e – e’)</i> (p<0.05). These results indicate that incentivizing the heat discrimination task reduced pain by increasing somatic focus. B. <b>Heat discrimination performance as a function of Task-Incentive Cue and Expectancy Cue.</b> Main effect of Task-Incentive Cue on Somatic Focus (corresponding to Path <i>d</i>): Participants performed at chance (dashed line) when visual task was incentivized, and above chance when heat-discrimination task was incentivized (p<0.001). Main effect of Expectancy Cue (high vs. low) on Somatic Focus (Path <i>a</i>): participants performed better on the heat discrimination task when they expected High pain (p<0.05). There was a significant interaction (dashed arrows in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038854#pone-0038854-g002" target="_blank">Figure 2A</a>) between Task-Incentive Cue and Expectancy Cue, such that heat discrimination task performance was better under High pain expectancy (p<0.001), while effects under Low pain expectancy were marginally significant (p = 0.03 one-tailed). C. <b>Pain ratings as a function of Task-Incentive Cue and Expectancy Cue.</b> There was a main effect of Expectancy Cue (corresponding to Path <i>c</i>), such that participants reported less pain when medium heat was preceded by low-pain cues, relative to high-pain cues (p<0.001). There was also a main effect of Task Incentive Cue (Path <i>e</i>), such that participants reported less pain during moderate-pain trials when they were preferentially rewarded for performance on the heat discrimination task, relative to the visual discrimination task (p<0.01). There was also a main effect of Somatic Focus (Path <i>b</i>), such that somatic focus reduced pain (p<0.001).