The relationship between visual motion detect thresholds and visual sensitivity to medial/lateral balance control

The ability to differentiate between self-motion and motion in the environment is important for maintaining upright balance control. Visual motion can elicit the sensation of a fall by cueing false position sense. This study explores the relationship between thresholds for visual motion detection (VMDTs) and visual sensitivity to balance disturbances while walking. Thirty young adults (18-35 years) and 30 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°, 10°, and 15°), and (2) performed 100 trials of a two-alternative forced choice (2AFC) task, discriminating 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). VMDTs were measured by fitting a psychometric curve to the 2AFC task responses. Significant positive correlations between measures of visual sensitivity and VMDTs were found for seven of nine conditions in young adults, with nonsignificant positive correlations in older adults. VMDTs were higher in older adults, though not significantly in the standing condition, indicating more motion in the environment is required for older adults to consciously perceive it. The positive correlations suggest that individuals with lower motion detection thresholds more accurately differentiate between self-motion and motion in the environment, resulting in lower responses to visual disturbances.