Weber's Law in walking: sensory scaling is observed in multi-sensory, dynamic tasks.

Behavioral flexibility requires adequate sensitivity to external stimuli to maintain optimal motor performance under evolving task demands. Empirical evidence shows sensitivity scaling follows Weber's Law, which states that sensory stimulus perception is scaled by background sensory context magnitude. However, Weber's Law has been assessed only in uni-sensory static tasks, and whether this principle extends to multi-sensory, dynamic motor tasks remains an open question. We assessed somatosensory perception of relative leg motion (i.e., speed differences between legs) in healthy young adults, hypothesizing that sensitivity to leg speed differences would follow Weber's Law. We estimated participants' sensitivity to speed differences (sensory stimuli) using two-alternative forced choice (2AFC) tasks. Participants walked at speeds representing distinct sensory contexts: slow (low-intensity), comfortable (medium-intensity), and fast (high-intensity). All groups compared their assigned testing speed against a common reference speed. We found that sensitivity to speed differences was consistent with Weber-like scaling at both slow and fast non-habitual walking speeds, but deviated near comfortable speed. Moreover, a drift-diffusion model using only reaction times reproduced the sensitivity scaling with walking speed, indicating that the model's evidence accumulation process can account for speed-dependent changes in perceptual sensitivity in multi-sensory, dynamic motor tasks.