Immersive Virtual Reality as a Rehabilitative Technology for

Phantom Limb Experience

Craig D. Murray*†, Stephen Pettifer**, Fabrice Caillette**, Emma Patchick* and Toby Howard**

*School of Psychological Sciences, University of Manchester, UK**School of Computer Science, University of Manchester, UK

Acknowledgement

The research reported here is supported by a grant from

What is Phantom Limb Experience?

Phantom sensation: widely accepted as a natural consequence of amputation

The experience of the amputated limb as still intact

Phantom Limb Pain (PLP): painful sensations in the phantom limb

Frequency of PLP as high as 85% post-amputationAs many as 70% of phantoms remaining painful up to 25 years after the loss of a limb

Affects of Phantom Limb Pain (PLP)

Overall adjustment to amputation is impaired as levels of pain increase

Less likely to use a prosthetic limb as levels of pain increase: Restriction of normal activities Increased body image dissatisfaction Higher levels of depression

Treating Phantom Limb Pain

Pharmaceutical, surgical and psychological interventions have proved to have limited success and longevity in treating PLP

?

Ramachandran and Rogers Ramachandran (1996)

Mirror placed vertically inside a box with the top removed

Reflection of their remaining anatomical limb in the phenomenal space of their phantom limbInduced vivid sensations of movement originating in the muscles and joints of their phantom limb

RESULT? Relief from PLP

Control gained over paralysed phantoms

Limitations of the Mirror Box

User must remain oriented towards the mirror:

Few degrees of freedom with movement of their head – need to focus on reflection no matter how large the mirror box is made

Illusion is easily shattered by focusing on the intact arm providing the reflection

Developing the Mirror Box

The mirror box contributes to a converging line of evidence that when feedback of limb movement is manipulated appropriately, it can evoke kinesthetic sensations in that limb

More robust visual therapy could potentially prove to provide greater therapeutic benefits than the mirror box:

Virtual Reality!

A contemporary, innovative technology that has already been exploited with some success in the amputee population

Immersive Virtual Reality (IVR)

Objectives

Create a new visual therapy for the treatment of phantom limb pain

Aims and Purpose

Produce virtual facsimilies of amputees’ phantom limb which can be controlled by movements of the opposite anatomical limb

Implement appropriate measures to objectively assess the efficacy of using IVR in this way to treat PLP

SECONDARY AIMS: Implement measures to assess the efficacy of using

IVR in this way to:

1. Decrease body image dissatisfaction2. Enable successful prosthesis use

How Does it Work?In order to transpose movements, we must first be able to track movements:

Upper Limb

Data gloveSensor -Wrist

Sensor - Elbow

Lower Limb

Sensor - FootSensor - Knee

For both, HMD tracks head position and orientation and to present the virtual environment to the eyes and facilitate immersion

For both, Polhemus Fastrak – emits magnetic field to monitor sensors

How Does it Work?Limb Position -Placing constraints on joint angles:

Impossible positions are avoidedAllows minimal sensors to fully ascertain limb position

Limb Movement -

Joint angles parametisation = ability to transfer from one limb to the other:

Joint angles recovered from active limbInverse kinematics applied and transferred to opposite virtual limbRESULT? Opposite virtual limb ONLY moves but in mirror image motion

Real-time transferral of joint angles =responsive fluent motion of virtual limbsCalibration - Real world points mapped onto virtual world

points i.e. Area of dance mat calibrated so no mismatch

Body Appearance - Deformable polygonal mesh attached to the underlying kinematic model for realistic results at a gross level. Detail sacrificed for responsive virtual limbsShadows - “Shadow-Map” facility allows shadows to be cast –

important for reaslism, sense of immersion and DEPTH PERCEPTION

How Does it Work?Interface on start up allows variations to be achieved at the click of a button :

How Does it Work?

How Does it Work?

How Does it Work?

How Does it Work?

Advantages of the System

Can orient anywhere in the virtual environment – more degrees of freedom of movement in the head

Only target limb (Phantom limb) is seen to move in virtual environment – illusion is more robust

Can engage in one-handed tasks – attention is focused more heavily on target limb

Transposition of movement can be more flexible – not just mirror movement

Can implement accurate, objective measures to assess task performance

Representation of the body can be altered to investigate aspects of body image

Potential for Further Development – Benefits of IVR System

Study Design and ProcedureLongitudinal study to assess any change in levels of PLP over time:

- Participants attend testing sessions at least once every 2 weeks for a period of 20 weeks (case study interventions also proposed)

- Tasks completed in repetitions for 30 minute sessions at a time

Between-subjects design Due to the nascent approach of using IVR to treat PLP, a control group is necessary to assess the outcome of treatment over and above any placebo affects:

- Experimental Group – visual representation of virtual phantom limb controlled by movements of the opposite anatomical limb

- Control Group – visual representation of virtual limb controlled by movements of the corresponding anatomical limb i.e. No transposition of movement carried out

Hypothesis – Experimental Group will experience significant short- and long- term reductions in the frequency and severity of PLP whilst Control Group will not. AND Experimental Group will experience significant positive changes in psychosocial issues, activity restriction and satisfaction with a prosthesis, whilst Control Group will not

Participants and Experimental Measures

ParticipantsCurrently being recruited via sub-regional Disablement Services Centre. 32 amputees = target sample (16 experimental, 16 control)

INCLUSION CRITERIA:Minimum 12 months post amputation with phantom limb painUnilateral, adult amputeesSuitable for being provided with a prosthetic limbExperimental Measures The following are completed once, one week prior to using

IVR system and again on completion of involvement with study:

1. The McGill Pain Questionnaire – indicates subjective global PLP experience

2. The Amputee Body Image Scale –assesses how an amputee perceives and feels about his or her body experience

3. The Trinity Amputation and Prosthetic Experience Scales – multidimensional self-report instrument to help understand adjustment to an artificial limb

Experimental Measures cont.

Since investigating the change in PLP over time is the primary goal of the research, we also want a continuous assessment of levels of PLP over time:

1. Short Form MPQ – administered at end of each IVR session

2. Pain Diaries – brief predominantly numerical diaries completed through course of involvement with study

Due to the highly subjective nature of phantom limb experience, brief semi-structured interviews with individual participants are carried out throughout the testing period to establish the phenomenology of their phantom limb

Covariate, Exploratory Measures for analysis: Mood Questionnaire – due to the nature of pain in

general and it’s variability with emotional disposition, a brief questionnaire to establish mood is carried out prior to each testing session

Vividness of Imagery - measure of participant’s ability to visualise movement in their phantom limb during IVR sessions

Data Analysis and Future Testing

Participants’ scores on the:

MPQ, short form MPQ, Pain Diaries ABIS and TAPES

Compared over the study period AND between the two VR conditions. This allows assessment of the short- and long- term therapeutic benefits of IVR for…

Transcribed interviews = exploratory qualitative analysis to contextualise the more quantitative findingsVividness of Imagery Questionnaire and Mood Questionnaire – exploratory covariates in analysis

Testing will begin shortly and updates on progress will be posted at:http://aig.cs.man.ac.uk/research/phantomlimb/phantomlimb.php

Phantom Pain ReliefBody Image Disturbance AND Prosthesis Satisfaction

Over and above any placebo affects

Thank-you for your time