Effect of instructive visual stimuli on neurofeedback training for motor imagery-based brain–computer interface

•We investigated the effect of watching visual stimuli during MI-based BCI training.•Viewing a dynamic human movement during MI enhances the spontaneous ERD production, which is useful for BCI.•Viewing a dynamic human movement during neurofeedback for MI-based BCI increases the training effect.•Observing a still photo of human forearms does not improve the spontaneous ERD production. Event-related desynchronization (ERD) of the electroencephalogram (EEG) from the motor cortex is associated with execution, observation, and mental imagery of motor tasks. Generation of ERD by motor imagery (MI) has been widely used for brain–computer interfaces (BCIs) linked to neuroprosthetics and other motor assistance devices. Control of MI-based BCIs can be acquired by neurofeedback training to reliably induce MI-associated ERD. To develop more effective training conditions, we investigated the effect of static and dynamic visual representations of target movements (a picture of forearms or a video clip of hand grasping movements) during the BCI neurofeedback training. After 4 consecutive training days, the group that performed MI while viewing the video showed significant improvement in generating MI-associated ERD compared with the group that viewed the static image. This result suggests that passively observing the target movement during MI would improve the associated mental imagery and enhance MI-based BCIs skills.