BALANCE SENSES MUSCLES BRAIN Sensory Integration Internal Map Balance is the consequence of an appropriate muscles activation processed by the brain fusion of sensory information

BALANCE MUSCLES BRAIN Sensory Integration Internal Map Vision, 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 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 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 AP direction: - Frequency INcreases moving forward (B) - Frequency DEcreases moving backward (B) - Volume increase going far from vertical position (A) ML direction: - Left/right ear volume channel increase moving left/right (CD) - Left/right ear volume channel decrease moving right/left (CD)

ABF instructions for the subject - Balance the sound between the two audio channels - Keep the lower volume (=400Hz sound wave) AP 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 Correlation between COP and trunk acceleration: - ML direction r: 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 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 APML APML 5 subjects: age: 30, (yrs), weight: 62, (kg), height: 166, (cm).

ABF information is SPECIFIC Providing ABF only in AP direction we affect mainly AP sway (RMS AP ) and AP control (MV AP ) AP and ML feedback ABF only for AP direction % parameters difference with ABF Root Mean Square distance Mean Velocity AP ML AP ML AP ML AP ML

With PRACTICE sbjs improves their skill to use ABF Sway Area decrease with practicing 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, Height: 171,

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) 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 Control Vestibular

ABF Tuning Fork effect Time [s] COM [degree] Platform rotation: 6 degrees, 1degree/s BVL subject PRE ABF WITH ABF POST ABF Plat. Rotation

Rambling & Trembling Analysis Rambling RMS Trembling RMS COP RMS Control Vestibular [mm] BVL subjects improve performance by reducing both rambling and trembling RMS CTRL subjects improve performance mainly by reducing rambling RMS RMS reduction using ABF

Effect of adding each sensory channel on Sway Area Adding ABF information decreases sway area Adding vision, somatosensory or vestibular information decreases Sway Area more than adding ABF Sway Area [mm 2 ] difference Sensory channels

ABF interacts similarly with all sensory channels Sway Area [mm 2 ] difference 0 Some subjects improve more than others with ABF when another sense is available Sensory channels

ABF controls subjects’ position Time [s] Displacement [cm] 7 Subject COP Sound 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) in the AP and in the ML direction

Slow frequencies are easier to follow Frequencies [Hz] AP ABF ML ABF Normalized Averaged Gain The gain was largest at the lowest frequencies and decreased with 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.

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

1 st 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

2 nd 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?

3 rd 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)?

4 th 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.