The Relationship Between Visual Motion Detection Thresholds and Visual Sensitivity to Medial/Lateral Balance Control

The ability to differentiate between self-motion and motion in the environment is an important factor for maintaining upright balance control. Visual motion can elicit the sensation of a fall by cueing a false position sense. While there is evidence supporting the role of central vision and fall risk, including measures of contrast sensitivity, depth perception, and size of the visual field, the relationship between motion detection thresholds and balance control remains unknown. The aim of this study is to explore the relationship between thresholds for visual motion detection (VMDTs) of the environment and measures of visual sensitivity to balance disturbances in the environment while walking. Thirty young adults (18-35 years) and thirty older adults (55-79 years) participated in a counter-balanced study where they 1) walked on a self-paced treadmill within a virtual environment that delivered frontal plane multi-sine visual disturbances at three amplitudes (6{degrees}, 10{degrees}, and 15{degrees}), and 2) performed 100 trials of a two-alternative forced choice (2AFC) task in which they discriminated between a counterclockwise ("left") and clockwise ("right") rotation of a visual scene under three conditions (standing, standing with optic flow, and walking). Visual sensitivity was measured using frequency response functions of the center of mass displacement relative to the screen tilt (cm/deg) while VMDTs were measured by fitting a psychometric curve to the responses of the 2AFC task. We found significant positive correlations between measures of visual sensitivity and VMDTs for 7 out of the 9 conditions in young adults, and nonsignificant positive correlations between the two measures in older adults. VMDTs were overall higher in older adults, although not significantly in the standing condition, indicating more motion in the environment is required for older adults to consciously perceive it. VMDTs also tended to increase from standing, standing with optic flow, and walking, although not significantly between the standing and standing with optic flow conditions for both populations. We interpret the positive correlations between the two measures as an indication that individuals with lower motion detection thresholds can more accurately differentiate between self-motion and motion in the environment, resulting in lower responses from visual disturbances in the environment.