TMS-induced motor activation increases visual awareness

The influence of non-perceptual information on visual awareness has recently gained substantial interest. Here, we investigated a potential contribution of evidence from the motor system to visual awareness ratings using single-pulse Transcranial Magnetic Stimulation (sp-TMS). We hypothesized that TMS-induced activation of motor cortex will increase the subjective awareness ratings as compared to sham stimulation. Additionally, we investigated whether TMS-induced motor evoked potentials (MEPs) could be treated as a measure of evidence accumulation resulting in behavioral response. Participants performed a visual identification task and rated their subjective experience with Perceptual Awareness Scale (PAS). During the task, we delivered sp-TMS and recorded MEPs with EMG placed on participants hand. Delivering sp-TMS to primary motor cortex resulted in higher average PAS ratings as compared to the control condition, but only in trials where stimulation was congruent with the response performed. Additionally, reaction times in the identification task were also higher in congruent trials. MEP amplitudes correlated with PAS ratings when response congruence was taken into account. We argue that activity in motor cortex influences visual awareness of the participants. Subsequently, MEP might serve as an indirect measure of both perceptual and non-perceptual evidence accumulated for visual awareness ratings. Finally, we conclude that the integration of additional information results in prolonged RTs in the identification task. Our results suggest that task-related motor activity influences visual awareness, extending the classical view on how visual awareness is shaped.