The effects of distant and on-line visual information on the control of approach phase and step over an obstacle during locomotion

Abstract

One of the goals of this study was to examine the nature and role of distant visual information sampled during locomotion in the feedforward control of leading and trailing limb while an individual is required to step over an obstacle in the travel path. In addition we were interested in whether or not on-line visual information available while the limb (lead or trail) is stepping over the obstacle influences limb trajectory control and whether the information provided during lead limb cross would be used to calibrate movement of the trail limb. Towards this end, we manipulated availability of vision following an initial dynamic sampling period during the approach phase in proximity to the obstacle and during the lead and trail limb stepping over the obstacle. Ten participants completed 40 trials of obstacle crossing in 8 testing conditions. Initial dynamic visual sampling was sufficient to ensure successful task performance in the absence of vision in the approach phase and during both lead and trail limb stepping over the obstacle. Despite successful task performance, foot placement of the lead and trail limb before obstacle crossing and limb elevation over the obstacle were increased after withdrawal of vision in the approach area. Furthermore, the correlation between toe clearance and foot placement was diminished. While both limbs require feedforward visual information to control the step over the obstacle, only lead limb elevation was influenced by availability of on-line visual information during obstacle crossing. Results were in agreement with the notion of primacy of information inherent in the optic array over those from static samples of the environment in guiding locomotion. It is suggested that the expected proprioceptive feedback information associated with the limb posture before the obstacle, reconstructed using visual memory from dynamic sampling of the environment, mismatched with those from the actual limb position. Accordingly, participants adopted a different strategy that enabled them to clear the obstacle with a higher safety margin.

Stepping over obstacles: Attention demands and aging

“…For the trail-foot to cross the obstacle, visual information may still be used, but in a feedforward manner in conjunction with online kinaesthetic sensory feedback [27]. The decreased trail-toe clearance in the oldest group of adults implies that this stage of obstacle crossing may require greater demands on cognitive resources than earlier stages.…”

Locomotor Adjustments Made by Toddlers While Stepping Over Obstacles

“…Specifically, fragile obstacles induced greater TC in the leading limb compared to rigid obstacles (Patla & Rietdyk, 1993) again suggesting that safety is essential in obstacle crossing and that it is ensured by vision (Mohagheghi, 2004).…”

“…In fact, the trailing foot position is adjusted in association with leading foot placement only if lead foot placement prior to the obstacle is changed due to absence of on-line visual information (Mohagheghi, 2004).…”

Comportamento locomotor de crianças de dois a seis anos em ambiente complexo

“…10,[12][13][14] Em estudos sobre o controle motor, os termos informação exteroceptiva (identificação visual da localização, das formas e superfícies existentes em determinado ambiente) e informação exproprioceptiva (identificação da relação entre os segmentos corporais e destes com os objetos e eventos no ambiente) são amplamente utilizados no sentido de oferecer recursos para a modulação ou adaptação do movimento durante o planejamento e realização de tarefa motora. 10,12,14,15 Além disso, os movimentos coordenados envolvem otimização da interação entre forças musculares e forças passivas. Para a realização e o controle de movimentos habilidosos, o indivíduo não apenas necessita controlar as forças passivas, mas também explorar as propriedades mecânicas passivas para dirigir e aumentar o movimento.…”