Locomotor adaptation is modulated by observing the actions of others

Observing the motor actions of another person could facilitate compensatory motor behaviour in
29 the passive observer. Here, we explored whether action observation alone can induce automatic
30 locomotor adaptation in humans. To explore this possibility we used the “broken‐escalator”
31 paradigm. Conventionally this involves stepping upon a stationary sled after having previously
32 experienced it actually moving (MOVING trials). This history of motion produces a locomotor
33 aftereffect when subsequently stepping on to a stationary sled. We found that viewing an actor
34 perform the MOVING trials was sufficient to generate a locomotor aftereffect in the observer, the
35 size of which was significantly correlated with the size of the movement (postural sway) observed.
36 Crucially, the effect is specific to watching the task being performed, as no motor adaptation
37 occurs after simply viewing the sled move in isolation. These findings demonstrate that locomotor
38 adaptation in humans can be driven purely by action observation, with the brain adapting motor
39 plans in response to the size of the observed individual’s motion. This mechanism may be
40 mediated by a mirror neuron system that automatically adapts behaviour to minimise movement
41 errors and improve motor skills through social cues, though further neurophysiological studies are
42 required to support this theory. This non‐verbal adaptive mechanism may have evolved to
43 facilitate motor conformity within social groups with respect to environmental hazards or risks.