Webers Law in walking: sensory scaling is observed in multi-sensory, dynamic tasks

We frequently adjust our behaviors in response to environmental changes. This behavioral flexibility requires adequate sensitivity to external stimuli to maintain optimal motor performance under evolving task demands. There is abundant empirical evidence that sensitivity scaling follows Webers Law. Webers Law states that the perception of a sensory stimulus is scaled by the magnitude of the background sensory context. However, Webers Law has so far been assessed only in uni-sensory static tasks, and it remains an open question whether this principle extends to multi-sensory, dynamic motor tasks. To address this question, we assessed somatosensory perception of relative leg motion (i.e., speed differences between right and left legs) in healthy young adults. We hypothesized that sensitivity to differences in leg speed would follow Webers Law. We estimated participants sensitivity to speed differences (sensory stimuli) using two-alternative forced choice (2AFC) tasks. Participants walked at a testing speed representing distinct sensory contexts: slow speed (low-intensity sensory context), comfortable speed (medium-intensity sensory context), and fast speed (high-intensity sensory context). All groups compared their assigned testing speed against a common reference speed. We found that sensitivity to speed differences followed Webers Law at both slow and fast non-habitual walking speeds, but this scaling differed when walking near the comfortable walking speed. Moreover, Webers Law scaling was reproduced by a drift-diffusion model that used only reaction times to quantify sensitivity, indicating that the evidence accumulation process described by the model can account for Webers Law scaling in multi-sensory, dynamic motor tasks, as well as in static, uni-sensory tasks. Author summaryAdapting motor behaviors to environmental changes requires precise sensory perception to maintain optimal performance. Webers Law, a fundamental principle of psychophysics, describes how sensory perception is scaled relative to background stimulus intensity to prevent sensory overload; however, its applicability to multi-sensory dynamic motor behaviors like locomotion remains unclear. Our results show that Webers Law partially explains how we perceive leg movement differences during walking. We found that sensitivity to speed differences scales following Webers Law when walking at non-habitual slow or fast speeds. However, near comfortable walking, people are actually more sensitive than at other speeds, departing from Webers Law. A drift-diffusion model replicated Webers Law scaling during walking, showing that the same mechanistic framework can explain the scaling of sensation in both static, uni-sensory tasks and dynamic, multi-sensory activities like walking.