Primed Action: Preserving Agency while Accelerating Reaction Time via Subthreshold Brain Stimulation

While prior work in neuroscience confirmed that transcranial magnetic stimulation (TMS) can shorten the onset of muscle activity, the implications of this reaction-time speedup have not been explored in interactive systems. We present Primed Action, a novel interface concept that leverages this type of TMS-based faster reactions. What sets Primed Action apart from prior work that uses muscle stimulation to “force” faster reactions is that our approach operates below the threshold of movement—it does not trigger involuntary motion, but instead it “primes” neurons in the motor cortex by enhancing their neural excitability. As we found in our study, Primed Action best preserved participants’ sense of agency than existing interactive approaches based on muscle stimulation (e.g., Preemptive Action). We believe this novel insight allows HCI researchers to implement new forms of haptic assistance that do not sacrifice agency, which we demonstrate in a set of interactive experiences (e.g., VR sports training).