1. The Study of Visually-Induced Postural Responses Using Virtual Environments
Sparto PJ, Furman JM, Jacobson JL,
Whitney SL, Hodges LF, Redfern MS
Department of Otolaryngology
University of Pittsburgh, PA, USA
Sponsors: Eye and Ear Foundation,
NIH: DC02490, DC05205, K25 AG001049

2. Collaborators Rolf Jacob, MD Kathryn Brown, MS, PT Jeffrey Jasko, BS
Leigh Mahoney, MS
Chad Wingrave, MS

3. Visually-Induced Postural Sway Research
Vestibular disorders (Redfern and Furman, 1994)
Anxiety disorders (Jacob et al., 1995)
Healthy elders (Borger et al., 1999)
Adaptation (Loughlin et al., 1996, Loughlin and Redfern, 2001)

4. Limitations Single rear-projected screen
Restricted in field of view (60 deg)
Not able to study peripheral motion cues
Modified Equitest platform
Pitch motion only
Frequency and amplitude range limited

5. Balance NAVE Automatic Virtual Environment (BNAVE)
Spatially-Immersive VR Facility used to generate moving visual environments
Can control many factors:
Field of view (180o H x 110o V)
Spatial and temporal characteristics of movement
Spatial frequency
Monoscopic & stereoscopic

6. BNAVE Layout

7. Sensory Integration Modified Neurotest posture platform
Pitch and A-P translation
Treadmill
Galvanic Vestibular Stimulation

10. Subjects Healthy Adults (CON) 5 Males, 6 Females
Age years, mean yrs
No abnormalities on clinical vestibular tests
Adults with Unilateral Vestibular Loss (UVL)
months post vestibular n. section

11. Stimulus Frequency of Movement 0.1 Hz 0.25 Hz
RMS velocity was 1.2 m/s for both freq.

13. Data Analysis
A-P Head Position sampled at 20 Hz using electromagnetic tracker
RMS amplitude of sway computed at stimulus frequency
Linear, Time-Invariant and Dynamic Systems Analyses

14. Adults – CON v. UVL

15. Phase-locked 0.1 0.3 0.5 0.7 0.9 10 30 50 70 Head PSD Frequency (Hz)10 30 50 70
Head PSD
Frequency (Hz) 10 20 30 40 50 60 70 80 -4 -2 2 4 6
Head Sway (cm)
Time (sec)

16. Not Phase-locked Head PSD 0.1 0.3 0.5 0.7 0.9 1 2 3 4 Frequency (Hz)1 2 3 4
Frequency (Hz) 10 20 30 40 50 60 70 80 -4 -2 2 4 6
Head Sway (cm)
Time (sec)

17. Phase-locking behavior
Controls (n=11)
Subjects with Unilateral Vestibular Loss (n=11)
0.1 Hz
0.25 Hz
Primary peak in PSD at stimulus frequency 7 4 6
Phase-lock during 1st cycle
Phase-lock for all subsequent cycles 5 3

18. 90
Phase v.
Frequency 3
120 60 2
150 30 1
180
210
330
UVL – 0.1
CON – 0.1
240
300
UVL – 0.25
CON – 0.25
270

19. 90
CON v. UVL
0.1 Hz 3
120 60 2
150 30 1
180
210
330
UVL – 0.1
CON – 0.1
240
300
270

20. 90
CON v. UVL
0.25 Hz 3
120 60 2
150 30 1
180
210
330
240
300
UVL – 0.25
CON – 0.25
270

21. Conclusions
Peripheral stimulus induces sway in ½ subjects at 0.1 Hz, and 1/3 subjects at 0.25 Hz
Subjects with compensated UVL sway the same amount as controls
Subjects with UVL have different timing at 0.25 Hz

22. Adults v. Children (8-12 y.o.)
Healthy Adults (CON)
5 Males, 6 Females
Age years, mean yrs
No abnormalities on clinical vestibular tests
Children
5 Males, 5 Females
Age years, mean yrs

23. Healthy Adults v. Children

24. Conclusions Greater sway at higher frequencies
Children aged 8-12 years still do not show adult pattern of visually-induced sway
Vestibular and somatosensory threshold for postural control may be higher

25. Conclusions
Visually-induced postural sway is a complex problem, dependent on many factors
visual field of view
optic flow structure
spatial and temporal frequency of stimulus
Relevant to many clinical problems

26. Current Areas of Research
Visual Influences in Height Phobia
Visual Influences in Migraine
Vestibular Rehabilitation using VR