Exploring the role of reduced optic flow in dynamic balance

Introduction

When optic flow-related visual feedback is reduced to zero (no scene motion with head motion), the amplitude of postural sway increases. However, there is limited work examining the amount of optic flow required to maintain stable (or baseline) amplitudes of postural sway, especially during dynamic stance tasks where there is an increased reliance on visual cues.

Objectives

The objective of the present study was to examine optic flow during dynamic stance and determine the amount of optic flow required before postural sway deviates from conditions with a gain of 1.

Methods

Twenty-six healthy adults stood on a force plate (used to calculate Centre of Pressure; COP) mounted to a motorized platform that pseudo-randomly translated continuously in the anteroposterior direction ( ± 5 cm, 0–1 Hz) for 60-s. Participants wore a virtual reality head-mounted display, used to show a virtual environment and assess head position (HeadPos). Optic flow-related visual feedback was reduced relative to head motion (0–1 in 0.25x increments). Amplitude and mean power (MP for four bands: LOW, 0–0.1 Hz; MED, 0.1–0.5 Hz; MED-HIGH, 0.5–1 Hz; HIGH, 1–5 Hz) of COP and HeadPos was used to quantify movement.

Results

COP and HeadPos amplitude, and MED-MP increased when optic flow gain was less than 0.5x.

Conclusions

Therefore, half the amount of optic flow-related visual feedback is enough to sustain levels of postural sway observed in real-world conditions (gain of 1). Visual contributions to dynamic balance control likely extend beyond previously theorized frequencies (<0.1 Hz in quiet stance), signifying the importance of vision during complex postural tasks.