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

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

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)

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

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

BNAVE Layout

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

Subjects Healthy Adults (CON) 5 Males, 6 Females Age 32 - 66 years, mean 49 + 11 yrs No abnormalities on clinical vestibular tests Adults with Unilateral Vestibular Loss (UVL) 10 - 72 months post vestibular n. section

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

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

Adults – CON v. UVL

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)

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)

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

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

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

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

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

Adults v. Children (8-12 y.o.) Healthy Adults (CON) 5 Males, 6 Females Age 32 - 66 years, mean 49 + 11 yrs No abnormalities on clinical vestibular tests Children 5 Males, 5 Females Age 8 - 12 years, mean 10 + 1 yrs

Healthy Adults v. Children

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

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

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