The document outlines a study that aims to determine if abnormal sensory re-weighting in fall-prone older adults is due to peripheral vestibular loss or central processing deficits, by comparing the postural control and sensory weighting of healthy young adults, healthy older adults, and fall-prone older adults during visual and somatosensory perturbations of varying amplitudes. The study will measure postural sway and gain responses to determine if fall-prone older adults demonstrate heightened sensitivity to visual and somatosensory cues regardless of vestibular function.

1. THEORY:
Sources of abnormal
sensory re-weighting in
fall-prone older adults
Gloria Ammons
Leslie K. Allison, PhD, PT
September 11, 2008

2. Postural Control
 Peripheral sensory inputs:
 Vision
 Somatosensation
 Vestibular
 Central processing
 sensory interpretation
 central integration
 map appropriate response
 activate muscular system

3. Deficient Sensory Processing
 Attributed to falls in the elderly
 Sources:
1. Peripheral sensory
 E.g. Bilateral vestibular loss
2. Central sensory integration
 E.g. “Pusher syndrome”
(Karnath 2003)

4. Sensory Re-weighting
 Allison et al. 2006; Oie et al. 2002; Maurer et al. 2006
 Central sensory process
 Sensitivity to change
 Up-weight
 Reliable sense
 Down-weight
 Unstable sense

5. Theory 1
 Allison et al. 2006
 Older adults vs. young adults
 Both able to “re-weight” senses accurately
to changing stimuli as long as older adults
are given enough time to adapt
 “weight” is measured by gain
Gain = peak response amplitude
peak stimulus amplitude
Allison et al. 2006: Fig 1

6.  Normal re-weighting:
 INTER-modality dependence
  visual display amplitude,  gain to vision stimulus motion
 INTRA-modality dependence
  visual display amplitude,  gain to somatosensory motion
Allison et al. 2006: Fig 4

7. Theory 2
 Peterka 2002
 Persons with known bilateral vestibular loss “weight”
vision & proprioceptive cues more highly than individuals
with intact vestibular function
Peterka 2002: Fig 3

8.  Despite screening for
peripheral sensory loss,
older adults “weighted”
vision & somatosensory
information more highly
than young adults
 Increased body sway 
higher gains
 Problem: inadequate
screening for vestibular
sensory loss?
Theory 3
 Allison et al. 2006; Borger 1999; Simoneau 1999
Allison et al. 2006: Fig 2

9. Purpose
 To determine if the source of abnormal sensory
re-weighting in fall-prone older adults is due to
peripheral vestibular loss or due to a central
processing deficit.

10. Hypothesis
 Fall-prone older adults with and without known peripheral
vestibular loss will both demonstrate sensory re-
weighting as measured by altered gain responses to
amplitude changes in visual and somatosensory motion
stimuli.
 Fall-prone older adults with intact vestibular function will
also demonstrate heightened sensitivity to vision and
somatosensory motion, indicating a central sensory
processing deficiency.

11. Importance
 Fall-risk increases with age
 15.9% of people  65 yrs reported falling at least once in 3 mo period
(CDC 2007)
 Falls & “fear of falling” are associated with activity avoidance, which
threaten independence among elderly (Stevens 2008; Bertera 2008)
 Exercise reduces risk for falls
 Current study will help:
 Promote EBP & future research
 Understand source of sensory processing deficits
 Develop effective fall prevention programs (Allison 2006)

12. References
1. Allison LK (2006) The dynamics of multi-sensory re-weighting in healthy and
fall-prone older adults. (Doctoral dissertation, University of Maryland, 2006).
Dissertation Abstracts International, 67 (6). (UMI No. 3222601)
2. Allison LK, Kiemel T, Jeka JJ (2006) Multisensory re-weighting of vision and
touch is intact in healthy and fall-prone older adults. Exp Brain Res 175:342-
352
3. Bertera EM, Bertera RL (2008) Fear of falling and activity avoidance in a
national sample of older adults in the United States. Health Soc Work 33:54-
62
4. Borger LL, Whitney SL, Redfern MS, Furman JM (1999) The influence of
dynamic visual environments on postural sway in the elderly. J Vestibl Res
9:197-205
5. Centers for Disease Control and Prevention [CDC] 2007 Web-based injury
statistics query and reporting system. National Center for Injury Prevention
and Control, Centers for Disease Control and Prevention. Accessed
September 10, 2008 from: www.cdc.gov/ncipc/wisqars
6. Jeka JJ, Allison LK, Saffer M, Zhang Y, Carver S, Kiemel T (2006) Sensory
re-weighting with translational visual stimuli in young and elderly adults: the
role of state-dependent noise. Exp Brain Res 174:517-527
7. Karnath H, Broetz D (2003) Understanding and treating “pusher syndrome.”
Phys Ther 83:1119-1125

13. References
8. Maurer C, Mergner T, Peterka, RJ (2006) Multisensory control of
human upright stance. Exp Brain Res 171:231-250
9. Oie KS, Kiemel T, Jeka JJ (2002) Multisensory fusion: simultaneous
re-weighting of vision and touch for the control of human posture.
Cogn Brain Res 14:164-176
10. Peterka RJ (2002). Sensorimotor integration in human postural
control. J Neurophysiol 88:1097-1118
11. Simoneau M, Teasdale N, Bourdin C, Bard C, Fleury M, Nougier V
(1999) Aging and postural control: postural perturbations caused by
changing the visual anchor. J Am Geriatr Soc 47:235-239
12. Speers RA, Kuo AD, Horak FB (2002) Contributions of altered
sensation and feedback responses to changes in coordination of
postural control due to aging. Gait Posture 16:20-30
13. Stevens JA, Mack KA, Paulozzi LJ, Ballesteros MF (2008) Self-
reported falls and fall-related injuries among persons aged  65
years – United States, 2006. Journal of Safety Research 39:345-349

15. METHODS:
Sources of abnormal
sensory re-weighting in
fall-prone older adults
Gloria Ammons
Leslie K. Allison, PhD, PT
October 7, 2008

16. THEORY
 Postural control is influenced by peripheral sensory inputs & central
sensory processing
 Both peripheral & central sensory deficits are associated with falls in
the elderly
 Normal sensory reweighting (SRW) is characterized by a pattern of
absolute gain responses to changes in environmental stimuli
 Increases in vision gain as visual input becomes more reliable;
 Decrease in somatosensory gain as vision becomes more reliable

17. THEORY
 No differences in pattern of gain response in young (HY), healthy
older (HO), & fall-prone older adults (FP) if given enough time to
adapt to changing stimulus
 People with known bilateral vestibular function loss (VFL) have
heightened sensitivity to changes in vision & proprioceptive cues
compared to people with intact vestibular function (VFI)
 FP also have heightened sensitivity to changes in vision &
somatosensation stimuli compared to HO & HY

18. PURPOSE
 To determine if the source of SRW in FP is due to:
 Peripheral vestibular loss or
 Central processing deficiency

19. HYPOTHESES
 Both HO & FP will demonstrate SRW as measured by altered gain
responses to amplitude changes in visual and somatosensory (SS)
stimuli
 All older adults with VFL will demonstrate heightened sensitivity to
vision & SS motion as measured by greater absolute gain responses
to the same stimulus.
 HO with VFI will not show heightened sensitivity to vision & SS
motion
 peripheral loss
 central impairment
 FP with VFI will show heightened sensitivity to vision & SS
 peripheral loss
 central impairment

20. METHODS

21. Subjects
 Sample
 3 groups of 30 each (total 90 expected)
 Healthy young (HY)
 age 18-30
 Healthy older (HO)
 age  70
 Fall-prone older (FP)
 age  70
 Selection
 Flyer
 Advertisements
 Personal contact
 Community
 ECU students
 Informed consent of experimental procedures
 Approved by University Institutional Review Board
Volunteers Needed
For Balance Study
If you are 70 years of age or older & have had
falls,
near falls,
or become much less steady than you were a year ago,
Please join the East Carolina University
Balance Study this summer/fall.
You will receive
FREE specialized balance testing
Up to $45.00 compensation for your participation
For more information, please call
Gloria Ammons at 252-327-9631
Leslie Allison at 252-744-6236
This study is funded by East Carolina University.

22. Subjects
 Exclusion Criteria
 Hx of psychological,
neurological, or
orthopedic disability;
 Consuming
medications that
impair balance
 Inclusion Criteria
 HY: Normal strength & ROM;
vision corrected to 20/20
 HO: No hx of falls; no reported
symptoms of imbalance; No AD;
have high physical activity level
 FP: Hx of falls or have high risk of
falls; reported incidence of
multiple near falls; reduced
functional activity level 2
imbalance; with/without AD

23. Experimental Apparatus
 Visual Display
 Rear-projected random star
field pattern
 Translucent 4m x 3m screen
 Software: Microsoft Visual
Studio 2005
 Central ellipse w/o stars
(Dijkstra et al. 1994)
 Refresh rate: 60 Hz

24. Experimental Apparatus
 Surface Motion
 NeuroCom v1.2.0
 Dynamic Dual Force Plate
 Raised platform
 A-P translation
 Measure GRF, estimated
COM
 Collected at 200 Hz

25. Experimental Apparatus
 Kinematics
 EVaRT v5.0.4 motion analysis
 6 cameras
 Infrared emitting diode markers
 3 head
 Bilateral acromioclavicular,
greater trochanters, lat.
femoral-tibial, lat. malleoli,
distal 5th metatarsals
 Calculate estimated COM
 Signals collected at 120 Hz

26. Experimental Protocol
 3 separate testing sessions for older adults
 Clinical screening session (2 hrs)
 Performed by PT & GA’s
 1st session to establish eligibility
 Tests:
 Visual Acuity - Snellen eye chart
 Mini-mental Exam
 Dynamic Handicap Inventory
 Berg Balance Scale
 1 Minute STS
 TUG
 LE strength screening
 LE somatosensation
 Touch - Semmes-Winstein
monofilaments
 Vibration - 128 Hz tuning fork
 Proprioception - PROM 1st ray & ankle

27. Experimental Protocol
 Vestibular Diagnostic Testing (3 hrs)
 Performed by audiologist & GA’s
 Tests:
 Hearing
 Videonystagmography
 Dynamic Visual Acuity Test
 Vestibular Evoked Myogenic Potentials (VEMP)
 Rotary Chair:
 Visual-Vestibular interaction
 Subjective visual vertical
 Multisensory Reweighting Experiment (3 hrs)

28. SRW Experimental Procedures
 Stand on force platform
 Face visual display
(distance of ~30”)
 Wear goggles
 Marker set
 Standardized foot
position (McIlroy & Maki 1997)
 Safety harness
 Limited auditory cues
during trials

29. Experimental Procedures
 Baseline data:
 Room lit
 Subject instruction
 Silent sync trigger
 Activates Neurocom &
EVaRT
 Collect:
 Standing calibration
 Static postural sway
 30 sec
 Dynamic LOS
 60 sec
 SRW data:
 Room darkened
 Subject instruction
 Silent sync trigger
 Activates Neurom, EVaRT,
& Visual
 Two stimuli - vision, &
somatosensation
 Stimuli have constant
frequency, varying amplitude
 Ten – 3 min trials
 Randomized conditions
 2’ seated rests between trials

30. Randomized
Conditions
Visual
stimulus
(ƒ = .28 Hz)
Somatosensory
stimulus
(ƒ = .20 Hz)
1 High amplitude
(8 mm)
Low amplitude
(2 mm)
2 Low amplitude
(2 mm)
High amplitude
(8 mm)

31. Data Analysis
Dependent Variables:
Gain
(amplitude)
Phase
(timing)
Independent
Variables:
Fall status HO
FP
Vestibular
function
Intact
(VFI)
Loss
(VFL)

32. Amplitude = peak COM displacement
Gain = peak response amplitude
peak stimulus amplitude

33. Gain
Allison et al 2006
INTER-modality dependence
INTRA-modality dependence

34. Phase
Allison et al 2006

35. Data Analysis
 P  0.05
 MANOVA
 Repeated measures
 2 x 2 Factorial design

36. References
 Dijkstra TMH, Schoner G, Giese MA, Gielen CCAM (1994)
Temporal stability of the action-perception cycle for postural control
in a moving visual observed with human stationary stance. Exp
Brain Res 97:477-486
 Hair JF, Anderson RE, Tatham RL, Black WC (1998) Multivariate
Data Analysis (5th ed). Prentice Hall
 McIlroy WE, Maki BE (1997) Preferred placement of the feet during
quiet stance: development of a standardized foot placement for
balance testing. Clin Biomech 12:66-70
 Allison LK, Kiemel T, Jeka JJ (2006) Multisensory re-weighting of
vision and touch is intact in healthy and fall-prone older adults. Exp
Brain Res 175:342-352

38. RESULTS:
Sources of abnormal
sensory re-weighting in
fall-prone older adults
Gloria Ammons
Leslie K. Allison, PhD, PT
December 2, 2008

39. Purpose / Hypotheses
 Purpose: to determine if the source of SRW in fall prone older adults is due
to peripheral vestibular loss or central processing deficiency
 Hypotheses:
1. Both young & older adults will demonstrate SRW as measured by
altered gain responses to amplitude changes in visual &
somatosensory (SS) stimuli
2. All older adults with vestibular function loss will demonstrate
heightened sensitivity to vision & SS motion as measured by greater
absolute gain responses to the same stimulus.
3. Fall prone older adults with intact vestibular function will also
demonstrate heightened sensitivity to vision & SS motion.

40. Experimental Methods
 3 groups of 30 each
 Healthy young (HY)
 age 18-30
 Healthy older (HO)
 age  70
 Fall-prone older (FP)
 age  70
 Experimental Apparatus
 Visual Display
 NeuroCom Surface Motion
 EVaRT Motion Analysis
 Protocol
 Clinical Screening Test
 Vestibular Testing
 MSWR Study

41.  MSWR Procedures
 Room lit for baseline data
 Static: postural sway
 Dynamic: limits of stability
 Room darkened for 10 trials (3 minutes each)
 Surface motion 0.28 Hz
 Visual motion 0.20 Hz
 5 conditions Hi to Lo amplitude (.8, .2)
 5 conditions Lo to Hi amplitude (.2, .8)
 Divided data into 4 segments: Hi pre, Lo post, Lo pre, Hi post

42. Experimental Design
 Independent variables
 Age
 Fall status
 Vestibular function
 Dependent variables
 Gain
 Phase
 P  0.05
 One way ANOVA
 Age (HY, HO, FP)
 vs. Gain
 vs. Phase
 Two way ANOVA
 Fall status, vestibular function
 vs. Gain
 vs. Phase

43. Actual Methods
 Pilot subjects: HY (2)
 MSRW
 NeuroCom – collect data points @ 200 Hz
 Calculate COM, gain, phase
Amplitude
Gain = COM response amplitude @ 0.2 Hz
stimulus amplitude @ 0.2 Hz
Phase = time difference between cycles
(position in degrees)

44.  Use a frequency response function to convert time data into
frequency data to understand the relationship between the input
stimulus (surface motion) and the output (postural sway)

45. Data Analysis
 N = 8
 Independent t test
 Condition (Hi, Lo)
 Vs. Gain
 Not significant
 Identified 2 outliers
 Ran Independent t test
 Significant p = 0.008 (df = 6)

46. Pilot 5: Hi pre (0.24), Lo post (2.36)

47. Pilot 3: Lo pre (10), Hi post (0.43)

48. Pilot Data Summary
 There was a significant difference between conditions Hi & Lo
amplitude and gain without outliers.
 Both subjects demonstrated SRW: Lower gain values in Hi condition
versus Lo condition.
Questions?