Performance of an attention-demanding task during treadmill walking shifts the noise qualities of step-to-step variation in step width

•Step-to-step variation of step width during treadmill walking is fractal.•Fractality is independent of step width and step width variability.•Performing an attention-demanding task during treadmill walking reduced fractality.•The attention demanding task increased step width and step width variability.•Only fractality discriminated walking with the attention-demanding task from not. The fractal scaling evident in the step-to-step fluctuations of stepping-related time series reflects, to some degree, neuromotor noise. The primary purpose of this study was to determine the extent to which the fractal scaling of step width, step width and step width variability are affected by performance of an attention-demanding task. We hypothesized that the attention-demanding task would shift the structure of the step width time series toward white, uncorrelated noise. Subjects performed two 10-min treadmill walking trials, a control trial of undisturbed walking and a trial during which they performed a mental arithmetic/texting task. Motion capture data was converted to step width time series, the fractal scaling of which were determined from their power spectra. Fractal scaling decreased by 22% during the texting condition (p