Characterization of the Sense of Agency over the Actions of Neural-machine Interface-operated Prostheses

Summary

Here we present a protocol which characterizes the sense of agency developed over the control of sensate virtual or robotic prosthetic hands. Psychophysical questionnaires are employed to capture the explicit experience of agency, and time interval estimates (intentional binding) are employed to implicitly measure the sense of agency.

Abstract

This work describes a methodological framework that can be used to explicitly and implicitly characterize the sense of agency developed over the neural-machine interface (NMI) control of sensate virtual or robotic prosthetic hands. The formation of agency is fundamental in distinguishing the actions that we perform with our limbs as being our own. By striving to incorporate advanced upper-limb prostheses into these same perceptual mechanisms, we can begin to integrate an artificial limb more closely into the user's existing cognitive framework for limb control. This has important implications in promoting user acceptance, use, and effective control of advanced upper-limb prostheses. In this protocol, participants control a virtual prosthetic hand and receive kinesthetic sensory feedback through their preexisting NMIs. A series of virtual grasping tasks are performed and perturbations are systematically introduced to the kinesthetic feedback and virtual hand movements. Two separate measures of agency are employed: established psychophysical questionnaires (to capture the explicit experience of agency) and a time interval estimate task to capture the implicit sense of agency (intentional binding). Results of this protocol (questionnaire scores and time interval estimates) can be analyzed to quantify the extent of agency formation.

Introduction

As robotic prostheses become increasingly advanced, the importance of relevant sensory feedback will continue to grow. Sensory feedback affects how humans perceive, interact with, and even integrate machines into their body schema. Recent NMI techniques can now provide prosthetic limb users with intuitive control and achieve sensations associated with touch^{1,2,3,4,5,6,7} and kinesthesia (movement sense)^8,....

Protocol

This protocol has been previously approved and follows the guidelines of the Cleveland Clinic’s human research ethics committee.

1. Hardware and Software of the NMI

1. Establish each individual participant’s NMI control and feedback so that when they attempt to perform a movement, they see and feel a virtual prosthesis complete that movement.
   1. Generate a hand kinesthetic percept through the participant’s NMI and capture the kinematics of the perceived moti.......

Discussion

Here a methodological framework is presented to characterize the experience of agency formed while operating sensate prostheses via NMIs. In this context, agency is particularly relevant as it bridges physical action to the background cognitive processes that shape perception. Through a participant's prosthesis and NMI, we have direct access to a number of key elements that establish the sense of agency: intent, motor output, and movement sensation. Of importance to advanced prosthetic limb control, the tool.......

Materials

Name	Company	Catalog Number	Comments
LabVIEW 2015, Service Pack 1, Version 15.0.1f2 64-bit	National Instruments, Austin, TX, USA	Full or Pro Version	We wrote custom software in LabVIEW to coordinate virtual prosthesis control with kinesthetic feedback as well as to present experimental conditions and record data.
8-Slot, USB CompactDAQ Chassis	National Instruments, Austin, TX, USA	cDAQ-9178
±60 V, 800 kS/s, 12-Bit, 8-Channel C Series Voltage Input Module	National Instruments, Austin, TX, USA	NI-9221
100 kS/s/ch Simultaneous, ±10 V, 4-Channel C Series Voltage Output Module	National Instruments, Austin, TX, USA	NI-9263
Custom Wearable Kinesthetic Tactor	HDT Global, Solon, OH, USA	N/A	This item was custom made. Other methods of delivering kinesthetic feedback are acceptable as long as the participant feels the sensation of the hand moving in real-time with the movements of the virtual hand.
MuJoCo Physics Engine, HAPTIX Version	Roboti LLC, Redmond, WA, USA	mjhaptix150	Newer versions of MuJoCo should be acceptable as well. We used the MPL Gripper Model.
Myobock Electrodes, powered by Otto Bock EnergyPack in MyoBoy Battery Receptacle	Ottobock, Duderstadt, Germany	electrodes: 13E200=60 battery: 757B21 battery receptacle: 757Z191=2	Any setup that provides an amplified, filtered, and rectified EMG or neural control signal could be used.