Successful Outcomes in a Stroop Test Modulate the Sense of Agency When the Human Response and the Preemptive Response Actuated by Electrical Muscle Stimulation are Aligned
The sense of agency (SoA) refers to the sensation that I caused the action. Generally, one would expect that if moved passively by an external force, one would not feel an SoA. However, Kasahara (2018) have found that by using precise timing, the SoA was elicited even for EMS-actuated preemptive passive body movement in a simple reaction time task. This effect however only has been verified in the specific situation where the participant and the EMS device share the same goal of action. (i.e., both participant and device press a button as fast as possible). Here, we studied a more complex situation where a participant cooperates with an EMS-based device to perform a choice-task. In this case, device and participants’ answers will not always be aligned, e.g., at times the EMS-based device can choose the wrong answer or vice versa. We hypothesized that, If the underlying mechanism of the SoA would prefer to depend on the cognitive process of verifying the goal of own action and the outcome retrospectively, the apparent in/correct outcomes modulate the participant’s SoA. Participants performed two-alternative forced choice tasks of the Stroop-test by tapping with both hands and the EMS also actuated the participant’s hand to respond to the task, faster or slower than the participant’s voluntary movement. The EMS played two roles: assistive (forced success) or adversarial (forced failure). The result showed that, when the participant’s response and the EMS response were aligned, the SoA was significantly higher when the outcome was success rather than failure. In contrast, when their responses were not aligned, the SoA was elicited only when the outcome reflected the participant’s response regardless of the EMS’ response. These results support our hypothesis partly and imply that only when the outcome is sensed as one’s action, its outcome modulates the SoA postdictively.