Fig. 2

FeetBack Stimulation and Experimental Protocol. (top left to right) The system logs a heel-strike when the force-sensitive sensor crosses an individualized threshold. It subsequently triggers the vibrotactile apparent movement stimulation on the corresponding side of the back, either in real-time or with an experimental delay. Participants walked along a 20 m by 4 m rectangle, so that they could complete one trial while walking along one of the longer sides. (lower left to right) To begin with, participants were asked to walk freely, at their preferred speed, so that baseline walking characteristics could be determined (B_PRE). Subsequently, participants wore the FeetBack system, personalized to the baseline gait characteristics, and received real-time tactile feedback about their on-going movements, triggered by each heel-strike (F := Familiarization). The main experiment was broken into four blocks (Intervention). Here, participants had to complete individual trials in which feedback was presented either in real-time (60 ms system delay) or randomly delayed by up to 1,500 ms. After each trial, participants reported their Motor Awareness by replying to the Yes/No forced-choice question: “Did the feedback you felt on your back exactly correspond to the walking you just performed?”