Fig. 1: Experimental protocol of EXP1 and EXP2.

A Left, schematic illustration of NF. In EXP1 and EXP2, β power of the signal recorded over the left motor cortex with EEG was computed and represented as a virtual gauge. Participants were asked to try to fill up the gauge for as long as it was presented on the screen, which required them to self-regulate their β power. Right, illustration of the NF conditions that were implemented in EXP1 and EXP2. In β-down (blue) and β-up (orange), the level of the gauge increased as participants respectively decreased and increased their motor cortical β power in regard to baseline values that were predetermined individually. Participants were encouraged to use motor imagery and relaxation/selective attention to facilitate self-regulation of their motor cortical β power in β-down and β-up, respectively. In Sham-Passive (gray), the level of the gauge varied according to β power from prerecordings and participants were asked not to try controlling the level of the gauge. B Top to bottom: name, duration, and illustration of visual stimuli that were presented on screen during each phase of a trial in EXP1 (top) and EXP2 (bottom). C Presentation order of blocks of trials in EXP1 (first row) and EXP2 (second and third rows). Blocks of trials are illustrated as colored rectangles in their order of presentation during the experiment, starting first with a block of familiarization trials. N refers to the number of trials included in each block. The color of the rectangles indicates the experimental condition that each block of trials pertains to (see legends on the right). The bidirectional black arrows indicate conditions that were counterbalanced across subjects (see “Methods” section for details).