Presentation on theme: "Virtual Agency, Embodiment and Analgesia in Phantom Limb Pain"— Presentation transcript:
1 Virtual Agency, Embodiment and Analgesia in Phantom Limb Pain Jonathan Cole, Greg Austwick, Richard Wynne, Jian Zhang and Chris Dawson.University of Bournemouth
2 Phantom Limb Sensation and Awareness “the subjective report of the awareness for a non-existing or deafferented bodypart in a mentally otherwise competent individual.” Weinstein, 1969.Up to 100%, i.e. it is normal.Vivid - try to walk on phantom legWide range of sensations, pressure, warmth, tickleEmbodied and OwnedPhantom Limb Sensation - ‘exteroceptive and or proprioceptive sensations; tingling, pressure, movement etc.’Phantom Limb Awareness - ‘ a general awareness of the presence of the limb.’Hunter et al, Brain, 2003
4 Phantom Limb Pain a majority of patients Not only after amputation - brachial plexus avulsion, nerve block spinal cord injurymoderate to severe in round 60% of those affected; in spinal injury pain in 60-65%, severe in 20-25%. In round 15% interferes with social activity, in 20% work and sleep (Kooilman, et al, Pain, 2000, 87, 33-41, Rose et al, Pain, 1988, 34, ).‘Injury does not stop life but pain can.’
5 Pathogenesis of Chronic Pain Deafferentation, equivalent to tinnitus,Overlander - studies on shinglesCentral reorganisation and plasticity,Flor - SEP and functional imaging after amputationMismatch between motor intention and sensory return, leading to pain associated with internal forward models unrestrained by peripheral feedback, or a breakdown in integrity of agencyRamachandran, Sirigu, Frith
6 Treatments for Phantom Limb Pain: imagined or observed movement of the phantom. 1. Below Knee Amputee swimming and playing golf.2. Mirror box:
9 Virtual re-Embodiment Limb construction in virtual spaceMotion capture at stump to drive virtual limb leading to…Virtual re-Embodiment and pain relief?
10 Computer GraphicsComputer graphics is now advanced enough, because of computer gaming technology to;allow the believable representation of human limbs in real-time.be affordable, by PCskinning, skeletal modelling and boundaries
12 A finished Polygon Model, ready for texturing and rigging
13 A polygon model of a hand that has been exported into Milkshape where ‘bones’ are added
14 The bones are used to deform the polygon model – the animation is done by manipulating the bones.
15 Modelling of hand with bounding spheres for collision detection
16 Motion Capture. Ascension Bird series; magnetic motion capture PCI Bird labNest of Birds in fieldup to 4 sensors, one source, sensitivity +/- 1mm in 1.8m radiuseach sensor provides position and orientation information in 3d, sampled at 103Hz, lag <10msecRuns off a Windows PC using MS Direct 3d for rendering (interface for graphics card, NVidia Quadro FX series. (Open GL supported in future.)NVidia stereoscopic extension to run a pair of I-glasses (VR specs – IO Systems, USA.)
18 Transformations between gesture and avatar. Motion of the gesture is used proportionally to alter the rotations of the major joints of the avatar arm to perform the required simulated gesture, aiming for a natural appearance and hence for embodiment.The grasp pre-set at a set distance between apple and hand which opens and shuts, using collision detection.Temporal lag between motion and avatar ~ 16 ms
19 Gesture complexity.Set avatar motion and grasp, and a single vector of motion capture, total motion ~ 40 mm, resting distance error +/- 2mms.A single subject motion produces a single action. Error from temporal and positional relation between the extent of shoulder movement and the extent of avatar movement.Is an action goal directed or towards the avatar?
22 Patient, sex and ageInjury and duration of painVAS pain, maximum and minimumMPQ rank and (weighted)ElectrodeplacementVAVSPain relief,VAS1 F, 83Rt forequarter amputation for tumour, Pain since8 to 2, half day each46, (47.9)Chest wallYes8 to 4.52 M, 37Rt C6-T1 root avulsion Pain since.7-8 2 hours per day, 2-3 rest46, (57.0)mid-humerus stumpNo3 M, 69Lt brachial plexopathy Pain from 6 months.8-9 to 3-4 round half time each44, (49.2)Elbow7-8 to 1-24 M, 36Rt forequarter amputation, Pain since.9 to 4. Severe most of the time.41, (46.6)8-9 to 25 M, 72Rt mid-humerus amputation, Pain/Discomfort since4 to 1-2 (less than half the time)16, (17)4 to 06 F 61Lt forequarterAmputation, pain developing.5 but sporadic only11, (11.2)VAS - visual analogue scale. MPQ – McGill Pain Questionnaire score. VA and VS – virtual agency and virtual sensation.
23 Phenomenology of virtual agency. A difference between ‘just’ seeing the avatar move and intending its movement, in terms of both the mental effort involved and the subsequent perception.‘It is much heavier and needs more effort to move the virtual arm than just to move the avatar from the shoulder alone.’This often did not involve the whole arm at once. ‘When trying to move the hand the fingers are stiff and seem to resist movement.’
24 Patient 4 - agency and analgesia. Pain Time, PhenomenologyVAS mins4 most of time before4 10 ‘novel feeling of moving the arm, hand still clenched’0 20 ‘can feel and move phantom arm and pain disappears into background’‘can feel and move arm, can feel hand, joints and knuckles and skin in hand when grasping, elbow less. It moves quickly when I do’‘when trying to move the fingers are stiff... I can feel the elbow coming from the stump and the hand on the end of it, but the two do not match up’‘the arm is now a gentle presence’
25 Patient 5 - agency and analgesia; Day 1. Pain Time, PhenomenologyVAS minsPain 8 most of time, up to 10 at times and for a third of the time 4.10 ‘can move the fingers a bit but not the rest’20 ‘the arm moves well with the fingers, it is still painful but is taking the pressure off’‘the wrist is beginning to move and I can feel a pressure in the arm trying to move’‘when I move the fingers and hand there is pressure but no pain, they are not being ripped off or squashed’
26 Patient 5 - agency and analgesia; Day 2. Pain VAS Time, mins Phenomenology9 0can move hand and fingers and feel them thembecame aware of some elbow pain once hand pain reducedfocussing on elbow once hand controlled20 elbow straightenedcan move fingers and hand with no pain therepain now in elbowc60 balance between mental concentration on agency
27 Perception and Intention Planner Motor command Movement Proprioceptive re-afferenceVisual re-afferenceefferenceSensory biasForward modelcomparatorComparatorMovement independent sensory input ?Modified from Tsakiris and Haggard 2005
28 Perception and Intention Planner Motor command Movement comparatorefferenceForward modelComparatorProprioceptive re-afferenceSensory biasVisual re-afferenceMovement independent sensory input ? PAINModified from Tsakiris and Haggard 2005
29 Perception and Intention Planner Motor command Movement Pain Perception reducedcomparatorefferenceForward modelComparatorProprioceptive re-afferenceSensory biasVisual re-afference ‘VIRTUAL’Movement independent sensory inputMovement dependent sensory inputModified from Tsakiris and Haggard 2005
30 Two failures of virtual agency and analgesia. The recovery of intention and action needed considerable mental effort, at least during these trials over, mostly, two days. As patients’ concentration tired then so did virtual agency and embodiment, and their pain returned. Typically during a day’s trial they would develop agency within 30 minutes or so and then have several hours with pain reduction.Two with no virtual agency: they had had paralysis of the arm for 5 and 18 years before amputation. (Ramachandran’s ‘learned paralysis?’) Interestingly one of these patients felt her phantom arm move in a mirror-box, and being touched by her other one in the mirror. Passive movement and sensation may be different to agency, active movement.