Avoidant instructions induce ironic and overcompensatory movement errors differently between and within individuals

Giving avoidant instructions can ironically result in the forbidden act being carried out, especially when the person is anxious or cognitive loaded. However, the consistency with which individuals make ironic errors across conditions remains unexamined. Forty participants were instructed to avoid moving a cursor above, below, left, and right when tracing an invisible line connecting two points while rehearsing seven-digit numbers on half of trials. Results showed that, without cognitive load, 26 participants made consistent overcompensatory movements, 10 made consistent ironic errors, and 4 showed no distinct error bias, with levels of somatic anxiety predicting this pattern. However, 21 (52.5%) participants changed their error tendency when cognitive loaded, indicating that movement effects of avoidant instruction were not experienced as general phenomena but rather differed between and within individuals. Overcompensatory errors made by participants grouped as overcompensatory performers under low load were significantly larger than the ironic errors made by participants grouped as ironic performers under low load, yet, paradoxically, ironic performers reported higher state and trait anxiety. Overall, results demonstrate a clear experimenter bias inherent in the use of avoidant instructions to direct participants' motor control.