Locomotor illusions are generated by perceptual body-environment organization

Abstract

While one is walking, the stimulation by one's body forms a structure with the stimulation by the environment. This locomotor array of stimulation corresponds to the human-environment relation that one's body forms with the environment it is moving through. Thus, the perceptual experience of walking may arise from such a locomotor array of stimulation. Humans can also experience walking while they are sitting. In this case, there is no stimulation by one's walking body. Hence, one can experience walking although a basic component of a locomotor array of stimulation is missing. This may be facilitated by perception organizing the sensory input about one's body and environment into a perceptual structure that corresponds to a locomotor array of stimulation. We examined whether locomotor illusions are generated by this perceptual formation of a locomotor structure. We exposed sixteen seated individuals to environmental stimuli that elicited either the perceptual formation of a locomotor structure or that of a control structure. The study participants experienced distinct locomotor illusions when they were presented with environmental stimuli that elicited the perceptual formation of a locomotor structure. They did not experience distinct locomotor illusions when the stimuli instead elicited the perceptual formation of the control structure. These findings suggest that locomotor illusions are generated by the perceptual organization of sensory input about one's body and environment into a locomotor structure. This perceptual body-environment organization elucidates why seated human individuals experience the sensation of walking without any proprioceptive or kinaesthetic stimulation.

Fig 1. The experimental setup.

(a) Seated male participant, with two vibratory devices attached to the sole of each foot, wearing a head-mounted display, via which he is being exposed to (b) a life-sized 3D virtual environment in which his virtual perspective while swaying like the head of a walking human was first moving forward across a meadow and then up a hill.

Fig 2. Comparison of gait sensations and other locomotion sensations.

Box-and-whisker plots of the scores for gait sensations and for other locomotion sensations in the locomotor structure trials and in the control structure trials. Bold horizontal lines indicate median overall rating score; boxes indicate the lower and upper quartiles; whiskers indicate the farthest data points within 1.5 times of the lower and upper quartiles, respectively. The circles depict the individual scale scores of the 16 participants.