The potency of optical and augmented reality mirror boxes in amputees and people with intact limbs

Ad ances in Elec ical and Elec onic Enginee ing 310 THE POTENCY OF OPTICAL AND AUGMENTED REALITY MIRROR BOXES IN AMPUTEES AND PEOPLE WITH INTACT LIMBS K. O’Neill 1,2 , A. de Pao 1,2 1 School o Elec ical, Elec onic and Mechanical Enginee ing, Na ional Uni e si y o I eland, Dublin (UCD),Bel ield, Dublin 4, I eland 2 Rehabili a ion Enginee ing, Na ional Rehabili a ion Hospi al, Dún Laoghai e, Co. Dublin e-mail:ann ao[email p o ec ed]e Summa y. Phan om limb pain is he dis essing p oblem expe ienced by many ampu ees, de ined as a pain ul sensa ion pe cei ed in he a ea o he missing body pa . Phan om limb pain can be e y se e e and disabling. I con inues o be expe ienced by wo hi ds o ampu ees, eigh yea s pos -ampu a ion. Augmen ed eali y has he abili y o change a pe son’s senso y expe ience. Mo e applica ions o his echnology a e g adually being u ilised o he apeu ic pu poses as augmen ed en i onmen s can be used bo h o dis ac he a en ion o pa ien s om exc ucia ingly pain ul expe iences and o p omo e co ical e-mapping a he si e om whe e he pain a ises. Using Augmen ed Reali y, an en i onmen has been c ea ed whe e uppe limb ampu ees can bo h iew and con ol mo ion o hei phan om limb o help alle ia e phan om limb pain. 1. INTRODUCTION The sensa ion o a phan om limb can be desc ibed as he eeling o he p esence o an ampu a ed ex emi y as s ill p esen . This phenomenon o a phan om limb has been ecognised o well o e a cen u y [1,2]. Almos e e yone who has a limb emo ed will expe ience a phan om limb, wi h mos ampu ees ha ing epo ed expe iencing a phan om immedia ely a e he loss o a limb [3]. Immedia ely a e ampu a ion, he phan om limb usually esembles he p e-ampu a ion limb in shape, leng h and olume. The sensa ion can be desc ibed as e y i id and o en includes eelings o pos u e and mo emen . In many cases, he phan om limb is p esen ini ially o only a ew days o weeks, be o e i g adually ades away om consciousness. Once he phan om ades away i gene ally does so comple ely, ye some ampu ees can ecall he phan om by ubbing he s ump o by in ense concen a ion [2]. Howe e , he phan om limb can also pe sis o yea s and may ne e ade away. 30% o pa ien s s ill ha e hei phan om limb decades la e [4] and case epo s exis ha de ail phan om limbs ha ha e pe sis ed o 44 yea s [5]. Phan om limb pain occu s when a pe son eels pain ha is a ibu ed o he a ea o a limb ha has been emo ed. Phan om limb pain can be se e e and disabling and con inues o be expe ienced by wo hi ds o ampu ees, eigh yea s pos ampu a ion [6]. As many as 70% o phan oms s ill emain pain ul 25 yea s a e he loss o he limb [7]. Phan om limb pain occu s in a iable o ms. In some ampu ees he pain is con inuous bu a ying in in ensi y, while o he s expe ience in e mi en pain o a high in ensi y [8]. Phan oms end o be mo e i id, and pe sis longe , a e auma ic limb loss, o ollowing ampu a ion o a p e-exis ing pain ul limb pa hology, han a e a planned su gical ampu a ion o a non-pain ul limb. I is o en epo ed ha a phan om limb will occupy a habi ual pos u e, bu spon aneous changes in posi ion a e also common. The phan om may also assume, ei he empo a ily o pe manen ly, an awkwa d and pain ul pos u e. Phan oms a e mo e i id and pe sis longe a e auma ic limb loss, o ollowing ampu a ion o p e-exis ing pain ul limb pa hology, han a e a planned su gical ampu a ion o a non-pain ul limb. This may be due o he g ea e a en ion paid o he mu ila ed o pain ul limb be o e i is los . Memo ies o he limb’s pos u e and o m p io o ampu a ion o en su i e in he phan om [9]. In addi ion, a e ampu a ion o a de o med limb, he de o mi y is o en ca ied o e in o he phan om [4,10]. Telescoping is a phenomenon ha is common in app ox. 50% o cases, especially in uppe -limb ampu ees. This is whe e he dis al pa o he limb is g adually el o app oach he esidual limb. In he case o an uppe limb ampu ee, he phan om a m ge s sho e o e ime un il he pa ien is le wi h jus a phan om hand a ached o hei s ump [11,12]. 2. CORTICAL BRAIN REMAPPING AFTER AMPUTATION The s udy o phan om limbs also p o ides an oppo uni y o unde s and exac ly how he b ain cons uc s a body image, and how his image is con inuously upda ed in esponse o changing senso y inpu s. A comple e soma o opic map o he body su ace exis s in he soma osenso y co ex o p ima es [13,14], including humans [15] (See Figu e 1). The soma osenso y co ex localises he sou ce o senso y inpu and pe cei es he le el o in ensi y o he s imulus. I is capable o spa ial disc imina ion, so i can disce n shapes o objec s being held o dis inguish sub le di e ences in simila objec s ha come in o con ac wi h he skin. The po ency o op ical and augmen ed eali y mi o boxes… 311 Fig. 1: Pen ield Homunculus shows whe e he si e o each limb is loca ed on he soma osenso y co ex o he b ain I has been shown ha co ical eo ganisa ion occu s a e ampu a ion [16] and ha he e is a high posi i e co ela ion be ween he magni ude o phan om limb pain and he amoun o co ical eo ganisa ion [17]. S udies o a m ampu a ion using magne oencephalog aphy ha e shown ha b ain a eas, which o dina ily ep esen he hand, we e ac i a ed when ei he he lowe ace o uppe a m was ouched [18,19]. S udies ha e shown ha when he ace o an ampu ee was s imula ed by ouch, senso y in o ma ion wen no only o he acial a ea o he co ex, bu i also in aded he si e ha , p io o ampu a ion, had ep esen ed he hand. The Pen ield Homunculus can be eo ganised o e a dis ance o 2-3cm in he adul b ain, ollowing loss o a limb [20,21,22]. In his way, he b ain ci cui y can be al e ed. 3. MIRROR BOX ILLUSION V.S. Ramachand an de eloped a echnique o ea phan om limb pain in uppe limb ampu ees by using an o dina y mi o [23]. The box is made by placing a e ical mi o inside a ca dboa d box wi h he oo o he box emo ed. The on o he box has wo holes in i , h ough which he subjec inse s his/he good a m and he phan om a m. (See Figu e 2) When iewed om sligh ly o -cen e, he e lec ion o hei “good” a m ga e he imp ession ha he subjec had wo in ac a ms. By sending mo o commands o he in ac a m o make symme ic mo emen s, as i conduc ing an o ches a, i gi es he imp ession ha he phan om a m has esu ec ed and he subjec ecei es posi i e isual eedback in o ming he b ain ha he phan om a m is mo ing in synch ony. This p ocess has been dubbed he Mi o Box Illusion and is he main basis o his s udy. Fig. 2: Demons a ing he Mi o Box Illusion The e is g ea a iabili y in he expe ienced au hen ici y o he mi o box illusion and i s abili y o alle ia e phan om limb pain. The e ec o his posi i e isual eedback o he ampu ee can be e y he apeu ic. In some cases i was possible o eposi ion phan om limbs ha we e pe cei ed o be held in pain ul o awkwa d posi ions, in o non- pain ul pos u es, gi ing empo a y elie om phan om limb pain. Whils his echnique had qui e d ama ic he apeu ic alue o some people, i was only mode a ely e ec i e, o comple ely ine ec i e o o he s [23]. 4. AUGMENTED REALITY MIRROR BOX The mi o box illusion had qui e d ama ic he apeu ic alue o some people, bu i was only mode a ely e ec i e, o comple ely ine ec i e o o he s. Fo hose ha ound i o be bene icial, i was possibly because he illuso y phan om p o ides eedback ha is consis en wi h ac ual phan om expe iences. Howe e ampu ees’ pe cep ions o hei phan om limbs o en di e g ea ly om hei o iginal limbs [24]. The phan om limb can be sho e , o longe , a y in hickness, ha e gaps o be con inuous, in compa ison o he o iginal limb. I is no unhea d o o a phan om limb o be disconnec ed om he ampu ee’s s ump (See Figu e 3). This is one eason why he mi o box illusion does no ha e any he apeu ic alue in some cases, as i is no uncommon o he e lec ed image o bea no esemblance o he phan om limb pe cei ed by he ampu ee. These i egula ly shaped phan oms canno be iewed in he mi o , as i necessa ily e lec s he image o he in ac a m. Fig. 3: The Phan om limb o his Ampu ee is pe cei ed o esemble a hand disjoin ed om he elbow s ump [24] Ad ances in Elec ical and Elec onic Enginee ing 312 We ha e c ea ed an en i onmen using Augmen ed Reali y ha simula es he mi o box illusion. I consis s o a 3-d g aphical ep esen a ion o an a m on a la sc een ha is con olled by a wi eless da a glo e (5DT Da a Glo e 5W, T ansmission F equency 433.92MHz.). The appea ance o he a m can be al e ed o esemble he phan om limb o he use . The da a glo e is wo n on he in ac a m, whils he phan om appea s on a la compu e sc een ha akes he place o he mi o . As he in ac a m mo es, he i ual a m on he sc een ep esen ing he phan om also mo es in unison. To c ea e he i ual ep esen a ion o an a m, we used he 3D G aphics anima ion package 3DS Max o de o m a single mesh objec . By a p ocess e e ed o as “Skinning”, we added a bone s uc u e o a de o mable mesh. When a bone is assigned o a mesh, i is gi en a se o e ices. These e ices a e weigh ed o de e mine how much in luence each bone has on he mesh. We wan ou mesh o bend a he join s o he a m, bu no in he middle o he o ea m when he e is mo ion in he bones (See Figu e 4). Skinning is he mos in ica e pa o he design p ocess as i dic a es how he mesh will de o m unde he in luence o each bone. Fig. 4: We se he in luence o he bones on he e ices in o de o ge he mesh o de o m p ope ly The main ad an age o he Vi ual Mi o is ha all ypes o phan om limbs, such as Figu e 3, can be g aphically ep esen ed on he sc een. In e ec , phan om limbs can be ailo ed o isually esemble wha he ampu ee pe cei es hem o be. Ano he ex a bene i ha he Augmen ed Reali y mi o has o e he gene ic Mi o Box is ha i can also be se up o gi e mo e gene al mo emen s, o example, mo ion o he i ual image in he same di ec ion as he in ac a m, o ha ing a hi d pa y con ol he mo ion o he image on he sc een. 5. EXPERIMENTAL STUDY Fou ampu ees and a con ol g oup o 22 able- bodied people pa icipa ed in he s udy unde condi ions o in o med consen and in acco dance wi h e hical p ocedu es. Ampu ee 1 is a 40 y old male who unde wen igh side abo e elbow ampu a ion necessi a ed by os eogenic sa coma. A e ampu a ion, he had he sensa ion ha his a m was in ac and in i s no mal posi ion. G adually, o e he pe iod o six o se en mon hs he expe ienced elescoping o his phan om. He now pe cei es his phan om hand o be a ached o he end o he esidual limb, he sec ion o he phan om ha o iginally joined he phan om hand o he esidual limb ha ing disappea ed o e ime. The phan om hand is el o be c amped in a claw-like posi ion, which al hough discom o ing is no pain ul. Ampu ee 2 is a 25 y old male who sus ained an ampu a ion o he igh o equa e and mino inju y o his igh leg when his mo o bike collided wi h a ca whose d i e was in oxica ed. His phan om a m is posi ioned ac oss his body as hough aised in a p o ec i e pose. Sensa ion is mos i id in he hand, which is held in a loosely clenched is wi h he humb on he ou side. Al hough he does no eel he o ea m and uppe a m pe se, he is awa e o he posi ion o he elbow. The phan om does no make in olun a y mo emen s and he canno olun a ily gene a e mo emen s in his phan om limb. Ampu ee 3 is a 64 y old emale who sus ained inju ies in a ehicle acciden leading o he subsequen ampu a ion o he igh a m below he elbow. She expe ienced phan om sensa ion immedia ely a e ampu a ion su ge y. She is no o dina ily awa e o sensa ion in he missing o ea m bu is awa e o he phan om hand. He inge ips a e el o be ouching he humb, and al hough o iginally el o be ouching he humb, he li le inge is now el o be aised. She does no expe ience he phan om inge s indi idually bu a he as one uni . When pain ul, he phan om hand is el as a clenched is wi h he nails digging in o he palm o he hand. Ampu ee 4 is a 42 y old emale who unde wen igh side abo e elbow ampu a ion a e a a ic acciden . She expe ienced he sensa ion o a phan om limb immedia ely a e ampu a ion. O e ime he phan om hand has elescoped, so ha she now pe cei es i o eside a he end o he esidual limb. When she expe iences phan om pain, he phan om hand is el as a clenched is wi h he nails digging in o he palm o he hand. Fo he con ol g oup, he subjec s consis ed o 8 males and 14 emales, anging in age om 20 o 29 (mean age = 24.91, s anda d de ia ion = 12.72). The pa icipan s we e asked o d aw a ca d om an unbiased deck o de e mine whe he hey would s a wi h he s anda d mi o o he Augmen ed Reali y e sion. This is o ensu e ha andomness was obse ed in he o de asks ha we e pe o med. (The p ocedu e desc ibed below is based on a subjec i s pe o ming he asks wi h he s anda d mi o box, be o e epea ing hem wi h he Augmen ed Reali y e sion. Fo hose ha selec ed The po ency o op ical and augmen ed eali y mi o boxes… 313 o pe o m he asks wi h he Augmen ed Reali y mi o box, he o de was simply e e sed). Ini ially, each subjec was in oduced o he mi o box illusion and he/she ied o expe ience he sensa ion o a phan om limb by opening and closing hei le hand in on o he mi o , as i hey we e conduc ing an o ches a and also o lex hei inge s acco dingly. The pa icipan s we e hen equi ed o y he mi o box illusion o 3 pe iods o 30 seconds, du ing which hey we e ins uc ed o epea edly close hei le hand in o a is , pause b ie ly be o e opening i ou again in on o he mi o . Then hey held hei hand ou s aigh and ben he hi d inge inwa ds be o e eleasing i . This ac ion was eplica ed by a andomly chosen inge (o he han he hi d digi ). This p ocess was epea ed o 3 pe iods o 30 seconds du a ion. Finally, he subjec s we e ins uc ed o place hei hand in on o he mi o la on a able and o d um hei inge s hy hmically agains he la su ace. The pa icipan s we e hen i ed wi h he le - handed 5DT da a glo e. They posi ioned hei le a m in on o he la sc een and hei igh a m behind i . An image o a igh a m appea ed on he sc een. The image used he e was a ealis ic 3-d ep esen a ion o a human a m. The subjec s we e ins uc ed o keep hei eyes ixed on he image on he sc een igh h oughou he expe imen . The same expe imen al p ocedu es as be o e we e ca ied ou , wi h he la sc een aking he place o he mi o . Fig. 5: Subjec using he Augmen ed Reali y Mi o Box, whils da a is being eco ded Finally, he subjec s we e asked o epea he expe imen s again using he Augmen ed Reali y mi o box. Howe e , his ime a ca oon-like image o an a m appea ed on sc een, di e en in p opo ion and shape o hei in ac a m. We measu ed he EEG signal om he si e on he co ex co esponding o he igh hand o de e mine whe he any ac i i y was occu ing in his egion. The mu hy hm was eco ded o e he senso imo o co ex o he b ain. The main elec ode placemen s o his a ea a e along he C line o he 10-20 sys em o elec ode placemen wi h C3 and C4 being used o eco ding o changes o mu hy hms associa ed wi h hand mo emen s [25]. Du ing ini ial mi o box expe imen s i was no ed ha he igh hand o some o he subjec s (held behind he sc een/mi o ) mo ed as he image on he sc een did. We ied o ack his mo ion by using wo small ligh -sensi i e accele ome e s. These we e aped o wo sepa a e himbles, which we e placed on he middle inge ip o each hand while he expe imen s we e being pe o med. We also eco ded an EMG signal om he igh a m as in some cases he mo emen o he igh hand was oo sligh o be obse ed by accele ome e s. The EEG, EMG and accele ome e signals we e only eco ded om he con ol g oup, as he idea behind hem only e ol ed a e es ing wi h he g oup o ampu ees. I is hoped o eco d hese eadings om he nex g oup o ampu ees. These cap u ed signals we e eco ded using a Biopac sys em and we e ed in o MATLAB ia a PCI- 6023E da a acquisi ion ca d om Na ional Ins umen s. 6. RESULTS Ampu ee 1 ound ha his phan om ini ially became ense while doing he expe imen s. I p oduced a pain ul sensa ion in he digi s ha we e mo ing, bu a elaxed sensa ion in he pa s o his phan om ha we e a es . The Augmen ed Reali y mi o had he same e ec o a lesse deg ee and esul ed in a less in ensi e phan om sensa ion han when he mi o was used. He epo ed ha he igh sensa ion in his phan om began o diminish and become milde o e ime, bu ha his phan om sensa ion became much s onge in all o his inge s. P io o es ing Ampu ee 2 was unable o p oduce olun a y mo emen in he phan om. The p o ision o eedback, whe he using a s anda d mi o o he augmen ed eali y box, p o ided him wi h no change in he posi ion o he phan om and did no al e his oli ional con ol o his phan om limb. Fo Ampu ee 3 isual eedback bo h in he s anda d mi o and augmen ed mi o condi ions in ensi ied and ex ended phan om expe ience, hough i was much mo e p onounced when using he augmen ed en i onmen . When using he s anda d mi o , she epo ed ha she could i idly eel he palm o he phan om hand, and ha his sensa ion could be el igh up h ough he a m. Viewing he augmen ed eali y phan om image acili a ed mo emen o he phan om o e inge as an independen digi . Such mo emen had p e iously been impossible. Mo emen o he inge s o he phan om hand could be emo ely gene a ed. Ampu ee 4 expe ienced he sensa ion o he phan om hand mo ing using bo h mi o echniques, bu ound ha i was mo e i id when using he Augmen ed Reali y mi o . She had ne e be o e expe ienced olun a y mo ion o he phan om limb. She was able o p oduce small mo ions o opening Ad ances in Elec ical and Elec onic Enginee ing 314 ou he phan om hand ha seemed o b ing empo a y elie om he phan om pain. A e he membe s o he con ol g oup had comple ed he s udy, i was shown ha all bu 2 o he pa icipan s ound ha hey could ag ee wi h he e ec c ea ed by he s anda d mi o box illusion. They ag eed ha he sensa ion o isualising hei e lec ion mo ing in unison wi h hei con olling a m was qui e ealis ic. When using he Augmen ed Reali y Mi o , 19 o he 22 subjec s ound ha he compu e gene a ed image esponded and beha ed in a con incing manne o ha o hei con olling a m wea ing he glo e (2 o hose who we e unable o expe ience a phan om sensa ion using he Augmen ed Mi o we e he same subjec s ha ound he s anda d mi o box illusion o ha e no e ec ). 16 subjec s epo ed ha hey we e con en ha he ca oon-like image beha ed easonably like a ealis ic one when using he Augmen ed Reali y mi o , bu many ound i o be a lo less con incing han he image o a p ope a m. Analysis o he accele ome e and EMG eadings indica e ha 12 o he subjec s subconsciously mo ed hei igh a m while pe o ming he asks. We we e able o de ec an inc ease in he ac i i y o he C3 si e in mos o he pa icipan s whene e mo ion occu ed in he image. While we expec ed o obse e his in he cases o people whose igh a m mo ed behind he sc een/mi o , i was in e es ing o no e an inc ease in ac i i y in some o hose whose igh a m emained s a ic h oughou he expe imen s. 7. DISCUSSION To da e, we ha e un o una ely been unable o ob ain a su icien numbe o igh -hand ampu ee olun ee s o his s udy in o de o ca y ou a p ope quan i a i e analysis. A p esen , ou ampu ees ha e ied bo h ypes o mi o box. Th ee o hese ound hem o ha e a bene icially he apeu ic e ec on hei Phan om Limb and assis ed hem in hei a emp o alle ia e Phan om Limb Pain. The o he ampu ee ound any a emp o inci e mo emen in his phan om ui less. P io o expe imen a ion, none o he ampu ees had been able o p oduce any la ge-scale olun a y mo emen o hei phan om limbs. Howe e , by using bo h mi o box echniques desc ibed he e o gi e mo emen o hei phan om limb, h ee o he ampu ees epo ed eeling a unique sensa ion ha none o hem had expe ienced be o e. Whils hese a e p elimina y esul s, hey a e none heless g ea ly encou aging, in ha h ee o he ou ampu ees es ed he Augmen ed Reali y mi o was able o p o ide some o m o elie om phan om pain. The ul ima e goal o his esea ch g oup is o c ea e an en i onmen using AR echnology ha will allow ampu ees o isually expe ience hei phan om limbs i s hand. They should be able o see hei phan om limbs as hey a e pe cei ed, as well as ha e he abili y o con ol hei posi ion, mo ion and o ien a ion. By ha nessing he po en ial o Augmen ed Reali y echnology, compu e gene a ed images o ampu ee’s expe ienced phan om limbs can be c ea ed in such a way ha hey mo e and look like hei own phan om expe ience. This b ings he he apeu ic alue o he isual illusion c ea ed by he mi o box o a wide ange o ampu ees. I may hen be possible ha Augmen ed Reali y has he po en ial o educe o maybe emo e phan om limb pain by he isual eedback ecei ed om he augmen ed en i onmen . 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