Virtual Hand with Ambiguous Movement between the Self and Other Origin: Sense of Ownership and 'Other-Produced' Agency

While previous research on body self consciousness has assembled that self and other origin movement are perceptually distinguishable, this protocol allows to make them ambiguous on the virtual hand. This method enables us observe a participant's experience as formed by sense of ownership and another produced sense of agency, rather than just the absence of these senses. To create videos for the pre and experimental sessions, first, set up a table and two chairs, a 35 by 60 centimeter white cushion hand rest tilted approximately 25 degrees and a display in the room in which the experiment will be conducted.

Mark the position of each material to be able to accurately reproduce the placement in subsequent sessions and place a 360 degree camera to be at eye level when the participant is sitting in one of the chairs. For the video for the male participants, have a male mock participant sit in the chair wearing a lab coat and put his left hand on the hand rest, with the palm facing up with the fingers not touching each other or the hand rest. Have a second researcher holding a paintbrush, sit in the other chair, facing the mock participant and start the recording to capture the stable condition video.

Play a reference tone and have the researchers stroke all of the mock participant's fingers with the paintbrush for 80 seconds. Have a second researcher place an approximately 30 centimeter kitchen knife with a 20 centimeter blade in the field of view of the camera and have the researcher quickly pretend to slash the mock participants wrist before disappearing. Then stop the recording.

For the slow condition video, have the researchers stroke the mock participant's hand again, changing the brush trajectory to avoid monotony. After 60 seconds, have the mock participant close and open all five fingers at a consistent slow speed for 20 seconds per open and closed cycle. Then have the second researcher show the knife and pretend to slash the mock participants wrist as just demonstrated before stopping the camera.

Film the fast condition video in the same manner but with the finger opening and closing performed in two second per open and closed cycle. Using the same researcher as in the videos, have a participant wear a lab coat and sit in the chair. After cleaning the participants right index and ring fingers with a wet wipe, attach silver silver chloride electrodes connected to an SCR data acquisition device to these fingers.

Have the participant keep the right hand down while not touching anything and instruct the participant to place the left hand on the hand rest, with the palm facing up while keeping the hand stable. Remind the participant to relax and inform the participant to look at the left hand when wearing the HMD. After giving the instructions, have the participant put on an HMD with a black screen and mirror the screen on the HMD onto the display on the table.

With the HMD showing a black screen, instruct the participant to put their left hand on the hand rest with the palm facing up and help the participant arrange the hand so that the fingers are not touching each other or the hand rest. Next, sit in the chair opposite the participant with headphones and a paintbrush and randomly select one of the videos that matches the gender of the participant. After announcing that the session is going to begin, start the video and brush the participants left hand using the same timing and position as demonstrated in the video, while the participant looks at the left hand through the HMD.

Use the mirror display to observe when the knife cuts in then show a black screen on the HMD for two minutes to allow the SCR to return to normal. At the end of the rest period, repeat the experiment with a different video until two trials have been performed for each of the three conditions in random order, asking the participant whether anything feels wrong physically after every two trials. When all of the trials have been completed, ask the participant if they saw that the hand was moved.

If the answer is not yes, ask whether the participant felt anything during the experiment. Next, ask if the participants saw the movement of the two speeds. If the answer is not yes, ask if the participant felt anything during the experiment.

Then ask the participant what they thought of the slower hand movement. As demonstrated in this representative analysis, SCR values in response to a knife threat showed no significant differences between the three conditions. However, when the SCR of the first and second duplicates were compared for each condition, a significant decrease in the response was observed in the condition with fast movement.

These data suggest that if obvious unpredicted movements are repeated, the illusory sense of ownership will disappear. If the movements are slow however, the sense of ownership will be maintained at the same level as that for no movement. In face-to-face interviews, none of the participants reported a sense of agency in the conventional sense.

Moreover, while type one participants simply denied their sense of agency, the attitudes for types two through four overlapped with their observed bodily movements. In addition, 13 out of 19 participants described the observed events as their own individual experiences that were formed by the generated sense of agency rather than rejection of the sense of agency. It is important to make a comfortable environment for the participant to draw their natural reactions.

Additionally, to establish trajectory accuracy is also the key. As a representative result shows the contradictory sensations rather represent a person's individual experience, indicating that this protocol enables us to post ambivalence of self-consciousness.