Controlling posture using an audio biofeedback

systemM. Dozza1,2, L. Chiari1,

R. Peterka2, F.B. Horak2, F. Hlavacka3

OHSU 1Dipartimento di Elettronica, Informatica e SistemisticaUniversità di Bologna, Italia

2Neurological Sciences InstituteOHSU, Beaverton (OR), USA

3Institute of Normal and Pathological PhysiologySlovenska Akademie Vied, Bratislava, Slovakia

Gio

vanni Seganti

ni, L

a p

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ice d

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ua,

1886

-188

7

“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 PRESERVEits 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

(van der Kooij, 2000)

BALANCE

SENSES

MUSCLESBRAIN

Sensory Integration

InternalMap

• Balance is the consequence of appropriate muscle activations processed by the brain fusion of sensory information

BALANCE

MUSCLESBRAIN

Sensory Integration

InternalMap

• Visual, Vestibular and Somatosensory information are used by the brain to perform balance

VISION

VESTIBULAR

SOMATOS.

AUDITORY

• ABF adds AUDITORY channel to provide trunk movement information

ABF components

Laptop withDAQ board

audioamplifier

Head-phones

SensoryUnit

force plate

• 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)

COP & Trunk acceleration are highly correlated

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0.06

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0

0.02

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0.06

0.08

0.1

COPAP

COPML

AAP

AML

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0

0.02

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COPAP

, COPML

[m]

AA

P ,

AM

L [

m/s

2] r = 0.90

r = 0.88

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

(E Gurfinkel, Agressologie, 1973)

Sensor characteristics

Accelerometricsensors

Amplifier andlow-pass filter

• 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)

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

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

Example of ABF signals

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)

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

ABF effects on standing

• Improve balance (Sway Area decreases)• Increase control (Mean Velocity increases)

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

Root Mean Square distance

Mean Velocity

Sway Area

AP ML

AP ML

5 subjects: age: 30, 23-33 (yrs), weight: 62, 58-78 (kg), height: 166, 160-179 (cm).

ABF information is SPECIFIC

Providing ABF only in AP direction we affect mainly AP sway (RMSAP) and AP control (MVAP)

AP and ML feedbackABF only for AP direction

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Root Mean Square distance

Mean Velocity

AP ML

AP

ML

AP ML

AP ML

With PRACTICE subjects improve their skill to use ABF

Sway Area decrease with practicing

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1 2 3

days

[mm

2]

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

Threshold

Bilateral Vestibular Loss Subjects

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

ABF reduces VESTIBULAR LOSS subjects’ Sway Area

Vestibular Loss Subjects reduce sway more than control subject when standing on foam with eyes closed

Control

95 % confidence ellipse (Sway Area)

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Vestibular

Sway Area % Reduction in Vestibular Loss subjects using ABF

This subject was able toperform the trials ONLYwith the help of ABF

This subject wasn't ableto perform thiscondition both with andwithout ABF

This subject fell twice without ABF but never fell during the trials using ABF

Bilateral Vestibular Loss subject 9

NO ABF WITH ABF

This subject can NOT stand on the foam with eyes closed.

This subject can stand on the foam with eyes closed using ABF.

% Reduction in Sway Area is consistent with residual vestibular

function

Time spent inside the Referencing Region increases using ABF

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BF

Control

Vestibular

ABF Tuning Fork effect

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M [

degr

ee]

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• Platform rotation: 6 deg, 1 deg/s

• BVL subject

PRE ABF

WITH ABF

POST ABF

Plat. Rotation

Rambling & Trembling Analysis

Rambling RMS

Trembling RMS

COP RMS

Control

Vestibular

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25

[mm]

• BVL subjects improve performance by reducing both rambling and trembling RMS

• CTRL subjects improve performance mainly by reducing rambling RMS

RM

S r

educ

tion

usin

g A

BF

(Zatsiorsky & Duarte, Motor Control, 1999)

Effect of adding each sensory channel on Sway Area

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4000

6000

8000

• Adding ABF information decreases sway area

• Adding vision, somatosensory or vestibular information decreases Sway Area more than adding ABF

Sw

ay A

rea

[mm

2 ] d

iffer

ence

Sensory channels

ABF interacts similarly with all sensory channels

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ay A

rea

[mm

2 ] d

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0

Some subjects improve more than others with ABF when another sense is available

Sensory channels

ABF controls subjects’ position

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Time [s]

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m]

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COPSound dynamic displacement • 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

Slow frequencies are easier to follow

1.20.05 0.1 0.2 0.4 0.6 0.8Frequencies [Hz]

AP ABFML ABF

Nor

mal

ized

Ave

rage

d G

ain

• 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.

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

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

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

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?

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)?

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.

Thank you for your attention

Luigi Galvani, Guglielmo Marconi and Augusto Righi, Bononiensi