Visual Motion Detection Thresholds Can Be Reliably Measured During Walking and Standing

In upright standing and walking, the motion of the body relative to the environment is estimated from a combination of visual, vestibular and somatosensory cues. Associations between vestibular or somatosensory impairments and balance problems are well established, but less is known about how the ability of the visual system to detect motion affects balance control. Here we asked whether motion detection thresholds can be reliably measured during walking and standing. Typically, motion threshold values have been obtained while sitting, with the head fixated to eliminate self-motion. In this study we 1) tested whether a visual motion detection threshold can be reliably measured during standing and walking in the presence of natural self-motion; and 2) investigated whether visual motion detection thresholds differ during standing and walking. MethodsTwenty-nine subjects stood on and walked along a self-paced, instrumented treadmill inside a virtual environment displayed on a large dome. Participants performed a 2-alternative forced choice experiment in which they discriminated between a counterclockwise ("left") and clockwise ("right") rotation of a visual scene projected on a large dome. A 6-down 1-up adaptive staircase algorithm was implemented to change the amplitude of the rotation. A psychometric fit to the participants binary responses provided an estimate for the detection threshold ResultsWe found strong correlations between the repeated measurements in both the walking (R = 0.84, p < 0.001) and the standing condition (R = 0.73, p < 0.001) as well as good agreement between the repeated measures with Bland-Altman plots. Average thresholds during walking (mean = 1.04 degrees, SD = 0.43 degrees) were significantly higher than during standing (mean = 0.73 degrees, SD = 0.47 degrees). ConclusionVisual motion detection thresholds can be reliably measured during both walking and standing, and thresholds are higher during walking.