Sensory perception of unexpected sudden changes in floor level during human gait

Possible clues for sensory perception of an unexpected sudden change in floor level during human gait could be discrepancies in the time of heel contact, location of force application point (center of pressure, CoP) in the sole at the heel contact and subsequent stance period from the ones prescribed prior to the gait execution prepared for the normal level gait, if they exist. In order to get insight for this perception mechanism, a psychophysical experiment during gait on a walk way with a small, unexpected and sudden change in the floor level was performed, in which the subject was forced to answer among step-down, flat, and step-up immediately after the walk. During the gait, foot pressure distribution (FPD), electromyogram (EMG) of the ankle muscles, and gait trajectory (GT) were measured. The experiment could quantify accuracy of the perception. The floor level change dependent changes in FPD, CoP trajectory, EMG, GT were examined to suggest that these changes might be the clues for the perception.