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					                  BALANCE
• Balance is the consequence of an appropriate muscles
activation processed by the brain fusion of sensory
information




                  Sensory            Internal
SENSES
                 Integration           Map

                                              BRAIN
             MUSCLES
                   BALANCE
• Vision, Vestibular and Somatosensory information are
used by the brain to perform balance
                                 • ABF adds AUDITORY
                  AUDITORY       channel to provide trunk
                                 movement information
VISION

VESTIBULAR          Sensory            Internal
                   Integration           Map
SOMATOS.

                                                BRAIN
              MUSCLES
                   ABF components
                                                           Head-phones
                                    audio
                                   amplifier               Sensory
                                                            Unit


       Laptop with
       DAQ board                          force plate

• Sensory Unit: provides accelerations trunk information
• Laptop with DAQ board: acquires the accelerations information and generates the
audio feedback signals
• Amplifier & Headphones: make audible the audio feedback signals
• Force plate: is NOT part of the system, has been used to acquire COP data for
ABF validation analysis
             Sensor characteristics

     Accelerometric
        sensors




                       Amplifier and
                       low-pass filter




• The sensor used is able to provide the full
complete kinematics of the trunk (3
accelerometers, 3 gyroscopes)
• ABF uses only 2-D acceleration (AP and
ML directions)
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 wideness)


              Referencing Region (RR)
              • represents the region for natural
              sway (1 degree)
              • is processed using the subject’s
              height
ABF sound generation functions
A   Volume
                          B   Frequency
                                                      AP direction:
                                                      - Frequency INcreases moving
                                                      forward (B)
                                                      - Frequency DEcreases moving
                                                      backward (B)
        AP acceleration             AP acceleration   - Volume increase going far from
                                                      vertical position (A)
C   Volume                      Balance
                          D

                                                      ML direction:
                                                      - Left/right ear volume channel
                                                      increase moving left/right (CD)
                                                      - Left/right ear volume channel
     ML acceleration             ML acceleration
                                                      decrease moving right/left (CD)
ABF instructions for the subject
                          - Balance the sound
                          between the two audio
                          channels




AP
- Keep the lower volume
(=400Hz sound wave)       ML
Example of ABF signals
  ABF practical considerations
• ABF can provide similar information as
  one otolith:
  – If the trunk/head moves slowly, primarily
    gravitational info is provided
  – If the trunk/head moves quickly, primarily
    acceleration information is provide

• Continuous ABF sound also provides trunk
VELOCITY information (most critical)
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
 COP & Trunk acceleration are highly
            correlated
                                                                                                            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
         0.08                                                                                                     0
                                                                    0
                0.06
                         0.04
                                                            -0.02
                                 0.02
                                        0                               COP
                                                    -0.04                     ML                          -0.02
                                            -0.02
                          COP
                                AP                                                                            -0.03   -0.02   -0.01   0         0.01           0.02         0.03   0.04          0.05        0.06

                                                                                                                                          COP          , COP          [m]
                                                                                                                                                AP               ML




Correlation between COP and trunk acceleration:
                - ML direction r: 0.88
                - AP direction r: 0.90
             ABF is EASY

• Subjects learn to use ABF in 1 minute

• Personal balance score is higher with ABF
  also when it is NOT really helpful

• It is really easy and comfortable to wear
     ABF effects on standing
• Improve balance (Sway Area decrease)
• Increase control (Mean Velocity increase)
ABF effect on CONTROL SBJs with
eyes closed and foam under the feet
                                      In this particular
                Mean Velocity
                                      condition the
                                      effects of using
                                      ABF are magnified
                                      since the sources
                    AP ML
       AP ML
                                      of information
                                      (senses) are more
                                      limited
                                      5 subjects: age: 30, 23-
                                      33 (yrs), weight: 62, 58-
    Root Mean
                                      78 (kg), height: 166,
    Square                Sway Area
                                      160-179 (cm).
    distance
ABF information is SPECIFIC
 AP and ML feedback
                                                         ABF only for AP direction
                                                                            Mean Velocity
   AP ML                                                 10




                      % parameters difference with ABF
           AP ML
                                                           5
                                                                 AP ML             ML
                                                           0
                                                                              AP
                                                          -5

Providing ABF only                                       -10

                                                         -15
in AP direction we
affect mainly AP                                         -20

sway (RMSAP) and                                         -25

AP control (MVAP)                                        -30

                                                         -35
                                                               Root Mean Square distance
    With PRACTICE sbjs improves
         their skill to use ABF


                                      Sway Area decrease with practicing
Within three days the
subject became so skillful
that he could stand on the            600
                                      500                      Threshold
foam with eyes closed        [mm 2]   400
maintaining his movement              300
inside the referencing                200
region i.e. not receiving             100
any additional information              0
from ABF                                        1         2        3
                                                       days
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
95 % confidence ellipse (Sway Area)
                                      Vestibular Loss
  -10
                                      Subjects reduce
  -20                                 sway more than
  -30                                 control subject
  -40
                                      when standing
                                      on foam with
                                      eyes closed
        Control     Vestibular
    % Reduction Sway Area 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
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.
  Time spent inside the Referencing
     Region increases using ABF
% difference using ABF




                         500
                         400
                         300
                         200
                         100
                           0


                 Control
               Vestibular
                    ABF Tuning Fork effect
                                             • Platform rotation:
               4                                       6 degrees,
                                                       1degree/s
COM [degree]




                                             • BVL subject
               2


               0

                                                   PRE ABF
               -2
                                                   WITH ABF

               -4                                  POST ABF

                                                   Plat. Rotation
               -6
                     4   8   12   16   Time [s]
Rambling & Trembling Analysis
                                   Control
                           25                                    • BVL subjects
RMS reduction using ABF




                                   Vestibular                    improve
                           20                                    performance by
                                                                 reducing both
                                                                 rambling and
                           15                                    trembling RMS

                           10                                    • CTRL subjects
                                                                 improve
                                                                 performance
                           5
                                                                 mainly by
                          [mm]                                   reducing
                                                                 rambling RMS
                                 COP      Rambling   Trembling
                                 RMS       RMS         RMS
                               Effect of adding each sensory
                                   channel on Sway Area
                             8000

                                                           • Adding ABF
Sway Area [mm2] difference




                             6000                          information
                                                           decreases
                                                           sway area

                             4000                          • Adding vision,
                                                           somatosensory
                                                           or vestibular
                                                           information
                             2000                          decreases
                                                           Sway Area
                                                           more than
                                                           adding ABF




                                        Sensory channels
                                    ABF interacts similarly with all
                                          sensory channels
                             4000
Sway Area [mm2] difference




                                                              Some subjects
                             3000                             improve more
                                                              than others with
                             2000                             ABF when
                               0
                                                              another sense is
                                                              available




                                           Sensory channels
                            ABF controls subjects’ position
                              Sound dynamic
                              displacement          Subject COP   • A sinusoidal function
                                                                  was added to the
                    7                                             acceleration fed back by
                                                                  ABF
                    6
                                                                  • The subject tried to
Displacement [cm]




                    5                                             keep constant the ABF
                                                                  tone following the sine
                    4
                                                                  function
                    3
                                                                  • The trial was performed
                    2                                             with different sine wave
                                                                  frequencies (.05, .1, .2,
                    1                                             .4, .6, .8, 1.2) in the AP
                                                                  and in the ML direction
                        0     20    40        60    80    100

                                         Time [s]
                                  Slow frequencies are easier to
                                             follow
                                                                              • The gain was largest
                                                                              at the lowest
                                                                              frequencies and
                                                         AP ABF               decreased with
Normalized Averaged Gain




                                                         ML ABF               increasing frequency
                                                                              • At the lowest
                                                                              frequencies (0.05Hz
                                                                              and 1Hz), subjects
                                                                              were unaware that the
                                                                              sound induced them to
                                                                              sway.
                                                                              •AP and ML sway
                                                                              induced different
                                                                              movement strategies.
                           0.05    0.1   0.2    0.4      0.6      0.8   1.2
                                          Frequencies [Hz]
              Conclusions
• ABF reduces sway
• ABF is comfortable and easy to
  understand for subjects
• Subjects increase postural control using
  ABF
• ABF information is specific and simple for
  the subjects to follow
       Future of ABF system

• 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 an external information closed
loop for sensory control
• 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 affect
  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.

				
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