Controlling posture using an audio biofeedback system

1. Controlling posture using an audio biofeedback system M. Dozza1,2, L. Chiari1, R. Peterka2, F.B. Horak2, F. Hlavacka3 OHSU 1Dipartimento di Elettronica, Informatica e Sistemistica Università di Bologna, Italia 2Neurological Sciences Institute OHSU, Beaverton (OR), USA 3Institute of Normal and Pathological Physiology Slovenska Akademie Vied, Bratislava, Slovakia

2. “The outset of a disease is never a mere loss or excess – there is always a REACTION, on the part of the affected organism or individual, to RESTORE, to REPLACE, to COMPENSATE FOR, to PRESERVE its identity, however strange the means may be” Oliver Sacks “The pathological physio-logy of the Parkinsonian syndrome is the study of an ORGANIZED CHAOS, a chaos induced in the first instance by destruction of important integrations, and reorganized on an unstable basis in the PROCESS OF REHABILITATION” Ivy McKenzie Giovanni Segantini, La portatrice d’acqua, 1886-1887

3. (van der Kooij, 2000)

4. BALANCE • Balance is the consequence of appropriate muscle activations processed by the brain fusion of sensory information Sensory Integration Internal Map SENSES BRAIN MUSCLES

5. BALANCE • Visual, Vestibular and Somatosensory information are used by the brain to perform balance • ABF adds AUDITORY channel to provide trunk movement information AUDITORY VISION Sensory Integration Internal Map VESTIBULAR SOMATOS. BRAIN MUSCLES

6. ABF components • Sensory Unit: provides trunk-kinematics information • Laptop with DAQ board: acquires and processes the trunk-kinematics to generate the audio feedback signals • Amplifier & Headphones: make audible and feed back to the subject the audio signals • Force plate: is NOT part of the system, have been used to acquire COP data for ABF validation analysis (Chiari et al., IEEE Trans Biomed Eng, submitted)

7. 0.1 A AP A ML r = 0.88 0.08 0.06 r = 0.90 ] 2 [m/s 0.04 ML , A AP 0.06 A 0.02 0.04 0.02 0.1 0 0.08 0 0.06 0.04 -0.02 0.02 0 COP -0.04 -0.02 ML -0.02 COP -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 AP COP , COP [m] AP ML COP & Trunk acceleration are highly correlated (E Gurfinkel, Agressologie, 1973) Correlation between COP and trunk acceleration (eyes closed condition): - ML direction r : 0.86±0.07 (CTRL) 0.84±0.09 (BVL) - AP direction r : 0.82±0.08 0.86±0.10

8. Sensor characteristics • The sensor used is able to provide the complete linear & angular kinematics of the trunk (3 accelerometers, 3 gyroscopes) • ABF in its present release uses only 2-D acceleration (AP and ML directions) (Giansanti et al., Proc. ISPG, Maastricht, 2001)

9. ABF control interface • Subject’s anthropometric data • Trial condition • Control ABF variable • Input frequency • Output frequency • Calibration and trial durations • ABF Direction • Velocity information • Threshold controller

10. ABF movement representation • Safety Region (SR) • represents the limit of stability • is the region in which the COM projection is inside the subject’s support base • the support base is processed on anthropometric parameters (feet length and width) • Referencing Region (RR) • represents the region for natural sway (±1 degree) • is processed using the subject’s height

11. Example of ABF signals

12. ABF practical considerations • ABF can provide similar information as one otolith: • If the trunk/head moves slowly, primarily gravitational information is provided • If the trunk/head moves quickly, primarily acceleration information is provided • Continuous ABF sound also provides trunk VELOCITY information (most critical)

13. ABF is EASY • Subjects learn to use ABF in 1 minute • Subjective balance score (Schieppati et al., JNNP 1999) is lower also when ABF seems NOT actually helpful • It is really easy and comfortable to wear

14. ABF effects on standing • Improve balance (Sway Area decreases) • Increase control (Mean Velocity increases)

15. ABF effect on CONTROL subjects with eyes closed and foam under the feet In this particular condition the effects of using ABF are magnified since the sources of information (senses) are more limited Mean Velocity AP ML AP ML 5 subjects: age: 30, 23-33 (yrs), weight: 62, 58-78 (kg), height: 166, 160-179 (cm). Root Mean Square distance Sway Area

16. AP and ML feedback ABF information is SPECIFIC ABF only for AP direction Mean Velocity ML AP 10 ML AP 5 ML AP ML 0 AP -5 Providing ABF only in AP direction we affect mainly AP sway (RMSAP) and AP control (MVAP) -10 % parameters difference with ABF -15 -20 -25 -30 Root Mean Square distance -35

17. With PRACTICE subjects improve their skill to use ABF Sway Area decrease with practicing Within three days the subject became so skillful that he could stand on the foam with eyes closed maintaining his movement INSIDE the referencing region i.e. not receiving any additional information from ABF 600 Threshold 500 ] 400 2 300 [mm 200 100 0 1 2 3 days

18. Bilateral Vestibular Loss Subjects 9 Subjects. Age: 55,38-73 Weight: 71,51-115 Height: 171,160-193

19. ABF reduces VESTIBULAR LOSS subjects’ Sway Area 95 % confidence ellipse (Sway Area) Vestibular Loss Subjects reduce sway more than control subject when standing on foam with eyes closed -10 -20 -30 -40 Control Vestibular

20. Sway Area % Reduction in Vestibular Loss subjects using ABF This subject was able to perform the trials ONLY with the help of ABF This subject wasn't able to perform this condition both with and without ABF This subject fell twice without ABF but never fell during the trials using ABF

21. Bilateral Vestibular Loss subject 9 WITH ABF NO ABF This subject can NOT stand on the foam with eyes closed. This subject can stand on the foam with eyes closed using ABF.

22. % Reduction in Sway Area is consistent with residual vestibular function

23. Time spent inside the Referencing Region increases using ABF 500 400 300 % difference using ABF 200 100 0 Control Vestibular

24. PRE ABF WITH ABF POST ABF Plat. Rotation ABF Tuning Fork effect • Platform rotation: 6 deg, • 1 deg/s • BVL subject 4 2 COM [degree] 0 -2 -4 -6 4 8 12 Time [s] 16

25. Rambling & Trembling Analysis (Zatsiorsky & Duarte, Motor Control, 1999) Control • BVL subjects improve performance by reducing both rambling and trembling RMS • CTRL subjects improve performance mainly by reducing rambling RMS 25 Vestibular 20 15 RMS reduction using ABF 10 5 [mm] COP RMS Rambling RMS Trembling RMS

26. Effect of adding each sensory channel on Sway Area 8000 • Adding ABF information decreases sway area • Adding vision, somatosensory or vestibular information decreases Sway Area more than adding ABF 6000 Sway Area [mm2] difference 4000 2000 Sensory channels

27. ABF interacts similarly with all sensory channels 4000 Some subjects improve more than others with ABF when another sense is available 3000 Sway Area [mm2] difference 2000 0 Sensory channels

28. ABF controls subjects’ position Sound dynamic displacement COP • A sinusoidal function was added to the acceleration fed back by ABF • The subject tried to keep constant the ABF tone following the sine function • The trial was performed with different sine wave frequencies (.05, .1, .2, .4, .6, .8, 1.2 Hz) in the AP and in the ML direction 7 6 5 4 Displacement [cm] 3 2 1 0 20 40 60 80 100 Time [s]

29. Slow frequencies are easier to follow • The gain was largest at the lowest frequencies and decreased with increasing frequency • At the lowest frequencies (0.05Hz and 0.1Hz), subjects were unaware that the sound induced them to sway. • AP and ML sway induced different movement strategies. AP ABF ML ABF Normalized Averaged Gain 0.05 0.1 0.2 0.4 0.6 0.8 1.2 Frequencies [Hz]

30. Conclusions • ABF is comfortable and well accepted by the subjects • Subjects increase postural control using ABF (area decreases, mean velocity increases) • ABF information is specific and simple for the subjects to follow • BVL subjects show a particular benefit to the exposure to ABF, during and after the session

31. Work in Progress • Development of a portable wireless prosthesis for balance improvement • Use in clinical rehabilitation for subjects with balance deficits • Validation of ABF during dynamic tasks

32. 1st Open question: What’s the best information we should provide with ABF? • Up to now we investigated the effect of providing trunk acceleration information • Also, ABF using CoP displacement was tested obtaining analogous results to trunk acceleration • Feedback of CoM displacement was less effective perhaps because it added a 30 msec delay

33. 2nd Open question: Where is the auditory information actually fused with the other sensory channels? • ABF adds a source of information to the sensory control of posture • Vision, vestibular and somatosensory information are fused by the brain to perform balance. Is ABF part of this elaboration? Does ABF require a different (voluntary) muscle activation strategy?

34. 3rd Open question: Can use of ABF become more automatic with practice? • We have shown that practicing with ABF increases subject’s balance performance • Vestibular loss subjects have difficulties using ABF when they are already controlling balance using a voluntary strategy i.e. concentrating specifically on the other senses (Divided Attention problem). Can use of ABF become more automatic (less voluntary)?

35. 4th Open question: What is the real effect of the foam? How do subjects adjust their strategy with foam under the feet? • We used the foam to simulate the lack of proprioceptive information but it also affects coordination • Foam provided reaction forces different from the those expected by the subject familiar with firm surface. • Subjects automatically, over a long period (days), learn how to remain stable on the foam and improve their ability to balance on the foam.

36. Thank you for your attention Luigi Galvani, Guglielmo Marconi and Augusto Righi, Bononiensi