The overall goal of this procedure is to estimate and visualize proprioceptive drift in 2D with free selection of the participant's hand position. This method can help answer key questions in psychophysics, engineering, and rehabilitation health, by exploring the method to operate a sense of self body. The main advantage of this technique is to estimate and visualize proprioceptive drift in 2D under the situation where the participant can select their hand locations.
Sense of self is originally discussed in the body rehabilitation research field. But now it's expanded to the engineering in the context of embodiment, such as virtual avatar and the artificial bodies. Begin by instructing the participant to perform a tapping movement by keeping the heel of their hand in contact with the mirror.
Then start the metronome at a tempo of 60 beats per minute. Instruct the participant to move both hands synchronously according to the sound of the metronome. Ensure that the timing of the participant's hand movements are close to one cycle per second by comparing it to the sound of the metronome several minutes after the tapping begins.
Begin by mounting a mirror or blackboard on the stand based on the condition. Use a mirror for the visual feedback condition and a blackboard for a counterbalanced condition without visual feedback. Sit the participant close to the mirror that is positioned along their mid-sagittal plane.
Ensure that the participant can only see the mirror image of their left hand and cannot see their real right hand. Next, instruct the participant to pay attention to the image of their left hand in the mirror during the experiment. Put retroreflective markers on the participant's right index fingertip and wrist.
Confirm with the participant that the haptic sensation of their right hand is not substantially altered by the markers compared to the left. Next, place noise canceling headphones over the participant's ears so that they will not hear the metronome. Instruct the participant to move their left hand 30 centimeters vertically and 30 centimeters horizontally from the lower right corner of the mirror, and to maintain this left hand position during the experiment.
Set this position as the origin of the surface of the 2D plane. Finally, instruct the participant to place their right hand on the other side of the mirror at any position and maintain its position until the end of the trial. At the beginning of a trial, instruct the participant to push the middle button of the foot pedal, which causes a beep through the headphone as feedback of the pedal press.
After the beep, instruct the participant to start tapping with both hands synchronously at one hertz on the mirror. After the participant completes six hand movements, instruct them to stop and answer a question about whether they feel the right and left hand are in the same position. Use the right foot pedal for yes, and the left foot pedal for no.
Then instruct the participant to move their right hand to another position of their choice. Then start the trial again as practiced. Ensure the participant understands the task, then begin the experiment.
Throughout the experiment, check that the timing of the participant's tapping stays at approximately one hertz by viewing the movements compared to the metronome. Allow a break after 100 trials and complete the experiment for the other condition on a separate day. Begin by defining 13 right hand positions for response collection on a questionnaire about sense of ownership and agency.
Inform the participant that they will complete the same procedure as before. After synchronously tapping the right and left hands six times, instruct them to orally answer questions about sense of ownership and agency using a seven-point Likert scale. Fill out the questionnaire's scores based on their responses.
Show ratings from negative three, meaning totally disagree, to positive three, meaning totally agree, with zero indicating neither agreement nor disagreement or uncertain. Ensure that the participant understands the task. Finally, move the participant's right hand to the next position and have them complete the trial again.
The area shapes where the participant could not detect the spacial offset between left and right hand position differ between the conditions. Furthermore, the area sizes and the condition with visual feedback are significantly larger than in the condition without visual feedback, suggesting that the required offset between visual and proprioceptive feedback to maintain proprioceptive drift is approximately 10 centimeters. Here the comparison between visualization of proprioceptive drift and questionnaire results for sense of ownership and agency shows that the offset areas to maintain these phenomena are concentric and almost overlap.
This technique can be completed in one hour if it is performed properly. Why attempting this procedure it is important to remember to check whether the participant's performed the task correctly. After it's development this technique pave the way for researchers in the field of psychophysics, engineering, and rehabilitation to explore this dimension method for sense of ownership and agency in multiple dimensions.
After watching this video you should have a good idea of how to estimate and human behavior during this experiment of the participant's right hand movement.
