Visualization Method for Proprioceptive Drift on a 2D Plane Using Support Vector Machine

Summary

This article describes a novel method to estimate proprioceptive drift on a 2D plane using the mirror illusion and combining a psychophysical procedure with an analysis using machine learning.

Abstract

Proprioceptive drift, which is a perceptual shift in body-part position from the unseen real body to a visible body-like image, has been measured as the behavioral correlate for the sense of ownership. Previously, the estimation of proprioceptive drift was limited to one spatial dimension, such as height, width, or depth. As the hand can move freely in 3D, measuring proprioceptive drift in only one dimension is not sufficient for the estimation of the drift in real life situations. In this article, we provide a novel method to estimate proprioceptive drift on a 2D plane using the mirror illusion by combining an objective behavioral measurement (hand position tracking) and subjective, phenomenological assessment (subjective assessment of hand position and questionnaire) with a sophisticated machine learning approach. This technique permits not only an investigation of the underlying mechanisms of the sense of ownership and agency but also assists in the rehabilitation of a missing or paralyzed limb and in the design rules of real-time control systems with a self-body-like usability, in which the operator controls the system as if it were part of his/her own body.

Introduction

In recent years, research about the sense or experience of the self-body, that is, one's own body, has increased in the context of embodiment. Embodiment refers to the idea or concept of having a physical or virtual body that can interact with the environment, such as reaching, grasping, and touching. For instance, humans can touch an object or another human positioned in the environment by moving their own body, in this case their own arm and hand. Nowadays, this interaction or communication is not limited to using one's own natural body. Due to inventions and development of human-like robots or avatars in the virtual world, the natural human body can be subs....

Protocol

All aspects of the experiment were approved by the Ethical Committee of Tokyo Institute of Technology.

1. Experimental Setup

1. Material and Setup for Measuring Proprioceptive Drift.
   1. Obtain a stand that can hold a 100 x 100 cm plate vertically (Figure 1).
   2. Obtain a chair on which the participant can sit comfortably during the experiment.
   3. Obtain a 100 x 100 cm acrylic mirror and matte blackboard.
   4. Obtain the position tracker (for example, SLC-C02, Cyverse) to track the participant's right hand position. Spatial resolution should be about 1.5 mm to allow sufficient number of samplings to be ....

Results

Representative results from a previous study are presented to illustrate the method¹⁶. Figure 3A shows that the area shapes where the participant could not detect the spatial offset between left and right hand position differed between the conditions with (mirror) and without (blackboard) visual feedback. Figure 3B shows that area sizes in the condition with visual feedback are significantly larger than in the condition without visual feedback .......

Discussion

We demonstrate a method to estimate proprioceptive drift in a 2D plane during the mirror illusion using SVM and to compare the result with questionnaire responses for sense of ownership and agency. This novel method revealed that the required offset between visual and proprioceptive feedback to maintain proprioceptive drift is approximately 10 cm and that this offset closely overlaps with the offset required to maintain the feeling of ownership and agency.

Note that the most critical step of t.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acric mirror
Matte blackboard
custom-made stand			e.g. wood pole or PVC(poly vinyl chloride) pipe
Chair
Foot pedal	P.I. Engineering	Classic X-keys USB, and PS/2 Foot Pedals	Other response device can be avaliable.
Position sensor	CyVerse	SLC-C02	Other position sensor can be avaliable.
Custom-made retroreflectivemarker		The marker provided by the motion capture vendor can be available.
Noise canselling head phone	bose	Quiet Comfort 3	Other head phone can be avaliable.
PC	Mouse computer	NG-N-i300GA	Other PC can be available.