Abstract
In attempting to walk rectilinearly in the absence of visual landmarks, persons will gradually turn in a circle to eventually become lost. The aim of the present study was to provide insights into the possible underlying mechanisms of this behavior. For each subject (N = 15) six trajectories were monitored during blindfolded walking in a large enclosed area to suppress external cues, and ground irregularities that may elicit unexpected changes in direction. There was a substantial variability from trial to trial for a given subject and between subjects who could either veer very early or relatively late. Of the total number of trials, 50% trajectories terminated on the left side, 39% on the right side and 11% were defined as “straight”. For each subject, we established a “turning score” that reflected his/her preferential side of veering. The turning score was found to be unrelated to any evident biomechanical asymmetry or functional dominance (eye, hand…). Posturographic analysis, used to assess if there was a relationship between functional postural asymmetry and veering revealed that the mean position of the center of foot pressure during balance tests was correlated with the turning score. Finally, we established that the mean position of the center of pressure was correlated with perceived verticality assessed by a subjective verticality test. Together, our results suggest that veering is related to a “sense of straight ahead” that could be shaped by vestibular inputs.
Highlights
People walking in a natural environment without stable external visual landmarks often get lost and come full circle
A trajectory was considered to deviate from the straight direction when the Y value was greater than 2 *Y-SD (Y-2SD)
We found that each subject preferentially placed the center of pressure (COP) on one side of the base of support (BoS): 9 subjects on the left side and 6 on the right side
Summary
People walking in a natural environment without stable external visual landmarks often get lost and come full circle. In the first studies that addressed this issue [1,9], it was claimed that when walking, swimming, driving a car, boat or a plane without vision, deviation was most of the time consistent in the same direction across trials Because he observed similar spiralshaped paths in various organisms, from spermatozoa to blindfolded humans, Schaeffer (1928) proposed that this was evidences for an ubiquitous spiraling mechanism and that ‘‘the same mechanism is at work in man that operates in the amoeba’’ [9]. None of the various explanations proposed for explaining veering behavior (differences in leg length or strength, biomechanical asymmetries, lateralization) can account for the behavior described in experimental findings, because they either suffered from methodological deficiencies in measuring veering or could not be reproduced [4]
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