Effect of medio-lateral (M-L) perturbations to the visual field on walking. Shown are mean step length, mean step width, RMS step length variability, and RMS step width variability (all shown as fraction of leg length L), and net metabolic rate (in both W/kg and dimensionless units). Comparisons are for the normal control condition without visual perturbations, and walking with translational M-L perturbations at arc length amplitude of 0.35 L (left and right bars, respectively). The M-L perturbations caused a significant increase in only three measures (asterisk * denotes P < 0.05), mean step width, RMS step width and net metabolic rate (20% increase, 65% increase, and 5.9% increase, respectively).