Changes in performance caused by positive and negative expectations (i.e., placebo
and nocebo responses) were found to play an important role in many aspects of motor
performance. This study aimed to test the impact of placebo/nocebo responses and the
assumed moderating role of dispositional optimism and anxiety on proprioceptive accuracy,
an essential aspect of motor functions. 78 undergraduate university students completed
questionnaires assessing dispositional optimism, state anxiety, and motivation to
cooperate, then were randomly assigned to three experimental groups. A sham subliminal
electric stimulation was applied with claimed positive (placebo group, n = 26), negative
(nocebo group, n = 26) or neutral (control group, n = 26) impact on proprioceptive
accuracy. Proprioceptive accuracy was measured with active and passive versions of
the Joint Position Reproduction task before and after the intervention. Expected and
perceived changes in performance were also assessed; changes in state anxiety, optimism,
and motivation to cooperate were used as control variables (covariates). Mixed analyses
of variance indicated that the experimental manipulation did not affect actual proprioceptive
accuracy but impacted expected and perceived performance. Adding the covariates to
the models did not substantially change the results. Further, no significant association
emerged between actual and perceived change in performance in the active test, and
only a weak correlation was found in the passive test. Expected performance did not
predict actual performance but predicted perceived performance in both tasks. The
results suggest that only perceived (subjective) aspects of proprioceptive accuracy
are susceptible to placebo and nocebo interventions.
