Group-level results.

<p>Histograms show the effects of the main independent factors (incentive and arousal levels) on the main dependent variables (grip force, effort rating). Grip force is expressed as a percentage of the highest measure. Effort ratings were divided by the actual force produced on a trial-by-trial basis. Error bars are ± inter-subjects standard errors of the mean. * Significant difference (paired t-test, <i>P</i><0.05), between negative and neutral picture and between 0.01€ and 1€ in the task. NS = non significant.