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Mobin Rastgar Agah

Temple Biomechanics Laboratory

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Each year one in every three adults age 65and older falls.

Falls are the most common cause of hospitaladmissions for trauma.

Falls are the leading cause of injury deathamong those age 65 and older. Over 18,000

older adults died from fall injuries in 2007.

Direct medical costs of falls totaled over $19billion in 2000.

Centers for Disease Control and Prevention

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Self-motiondetection &

posturalcontrol

Vision

Vestibularsystem

Somatosensory

System

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A good prototype for stability of entirebody

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CCR (cervico-collic reflex)Automatic response of neck muscles to activation of themselves

VCR (vestibulo-collic reflex)

Automatic response of neck muscles to vestibular system Visual reflex

Automatic response of neck muscles to visual input

Voluntary mechanisms

These mechanisms work together to stabilize the headaround the direction of gaze.

Pozzo T. et. al. (1990). Exp. Brain Res., 82, 97-106Pozzo T. et. al. (1989). Progr. Brain Res., 80, 377-383

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Visual stimulation can induce self-motion perception.

Accurate detection of inertial motion decreases in presenceof stationary visual input.

Correct detection of self motion in case of discordantvisual flow is lower than concordant visual flow.

Misaligned visual motion (wrt inertial motion) dominates theself-motion perception.

Wright W.G. et. al. (2005). J. vestibular Res., 15, 185-195Ohmi M. et. al. (1996). Cogn. Brain Res., 5, 87-96

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Our hypothesis is that:

Visual input dominates the head stability at certain lower

frequencies (~ 0.2 Hz) of inertial input while the vestibularmechanism determine the head movements at higherfrequencies (~ 2 Hz).

This can help to design standard tests in order to find thepotential source of fall for those who are at risk .

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Race car seat

5 point harness belt

Feet straps Frame and platform

The body can be fixed in thechair properly with onlyhead and neck free.(Corbea - Sandy)

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Track and sled

Servomotor

Modular Drive System PowerTools software

~ 1.5m amplitude

0.1 to 5 Hz frequency

(WH120 - WIESEL SPEEDLine)(MH8500 Control Techniques)(MD434 Control Techniques)

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1-axis Gyroscopes

3-axis accelerometers

2-axis accelerometers

(ADXL320EB, 5g Analog Devices)(ADXL335Z , 3g Analog Devices)(ADXRS624, 50o/s Analog Devices)

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Camera

Head mount

HMD (Head MountDisplay)

(203CA-1 - Pine Computer)(HR920-3D, i-o Display Systems

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Labview software

Signal Conditioning

Data Acquisition card

Sampling frequency of1000 Hz

(SC2311 National Instruments)(PCI6281-National Instruments)

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Eyes open, Eyes closed, Backward ,Sid-ways

3 trial for each visualinertial condition

Linear sinusoidal motion with frequencies:

0.1, 0.2, 0.5, 1.1

Linear acceleration of head and sled

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Initial data analysis with transformfunctions showed no significant differences.

Using Approximate Entropy (ApEn)revealed significant differences betweencertain conditions.

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Measures regularity of time series as anumber between 0 and 2.

Larger numbers corresponds to noisy(unpredictable) signal.

Pincus, S. M. (1991). Approximate entropy as a measure of systemcomplexity. Proceedings of the National Academy of Science, 88, 2297-2301.

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ApEn = 0.247

ApEn = 1.812

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Approximate Entropy at 0.2 Hz frequency

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AccY 0.2 Hz

EO-SW

EC-SW

BW-EO

(p=0.03)

(p=0.05)

(p=0.042)

AccY 0.5 Hz BW-SW (p=0.01)

AccZ 0.2 Hz EC-EO (p=0.002)

AccZ 0.5 HzBW-EC

BW-EO

(p=0.035)

(p=0.039)

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Focusing on frequencies between 0.2 and0.5 Hz for visual input

Movement of head in local coordinate

Lowering the noise level in data

Choosing consistent sampling frequency

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More subjects

More realistic HMD (already obtained)

Different computer generated visualconditions (Virtual reality)

Motion analysis systems to verify the data

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Questions?

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Semicircular canals detect rotational motion.

Otolithic organs detect linear acceleration

Figure fromWikipedia

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