Abstract
The aim of this preregistered EEG study was to show how expectations about enhanced or impaired performance through transcranial stimulation affect feelings of agency and error processing. Using a single-blind experimental design, participants (N = 57) were attached to a transcranial direct current stimulation (tDCS) device, and in different blocks, they were verbally instructed to expect enhanced or impaired cognitive performance, or no effects of the brain stimulation. In all cases, but unbeknownst to the participants, we used an inert sham tDCS protocol. Subsequently, we measured their response to errors on a cognitive control task. Our expectancy manipulation was successful: participants reported improved subjective performance in the enhancement compared with the impairment condition—even though objective performance was kept at a constant level across conditions. Participants reported the highest feelings of agency over their task performance in the control condition, and lowest feelings of agency in the impairment condition. The expectancy manipulation did not affect the error-related negativity (ERN) in association with incorrect responses. During the induction phase, expecting impaired versus enhanced performance increased frontal theta power, potentially reflecting a process of increased cognitive control allocation. Our findings show that verbally induced manipulations can affect subjective performance on a cognitive control task, but that stronger manipulations (e.g., through conditioning) are necessary to induce top-down effects on neural error processing.