When Is Visual Information Used to Control Locomotion When Descending a Kerb?

Abstract

BackgroundDescending kerbs during locomotion involves the regulation of appropriate foot placement before the kerb-edge and foot clearance over it. It also involves the modulation of gait output to ensure the body-mass is safely and smoothly lowered to the new level. Previous research has shown that vision is used in such adaptive gait tasks for feedforward planning, with vision from the lower visual field (lvf) used for online updating. The present study determined when lvf information is used to control/update locomotion when stepping from a kerb.Methodology/Principal Findings12 young adults stepped down a kerb during ongoing gait. Force sensitive resistors (attached to participants' feet) interfaced with an high-speed PDLC ‘smart glass’ sheet, allowed the lvf to be unpredictably occluded at either heel-contact of the penultimate or final step before the kerb-edge up to contact with the lower level. Analysis focussed on determining changes in foot placement distance before the kerb-edge, clearance over it, and in kinematic measures of the step down. Lvf occlusion from the instant of final step contact had no significant effect on any dependant variable (p>0.09). Occlusion of the lvf from the instant of penultimate step contact had a significant effect on foot clearance and on several kinematic measures, with findings consistent with participants becoming uncertain regarding relative horizontal location of the kerb-edge.Conclusion/SignificanceThese findings suggest concurrent feedback of the lower limb, kerb-edge, and/or floor area immediately in front/below the kerb is not used when stepping from a kerb during ongoing gait. Instead heel-clearance and pre-landing-kinematic parameters are determined/planned using lvf information acquired in the penultimate step during the approach to the kerb-edge, with information related to foot placement before the kerb-edge being the most salient.

The addition of stripes (a version of the ‘horizontal-vertical illusion’) increases foot clearance when crossing low-height obstacles

“…Evidence suggests that vision plays a vital role in successful obstacle and stair negotiation (Templer 1992;Patla and Vickers 1997;Startzell et al 2000;Marigold 2008;Elliott 2014). Essentially vision is used in a feed-forward manner to plan negotiation of the obstacle and then information from the lower visual field is used online to update/fine-tune foot placement before the obstacle and clearance over it (Graci, Elliott, and Buckley 2010), with information regarding final foot placement being critical to such fine-tuning (Buckley et al 2011;Timmis and Buckley 2012).…”

The effect of muscle fatigue on the last stride before stepping down a curb

“…The approach to a curb may be of crucial importance in preventing falls, since the stepping strategy appears to be planned based on visual information obtained during the penultimate step [7]. Moreover, adequate foot placement in the last step before the curb may be fundamental, since errors may result in a misstep on the curb [8,9].…”

Longitudinal changes in transtibial amputee gait characteristics when negotiating a change in surface height during continuous gait

“…(COM) via eccentric muscle actions and conversely, when stepping up 52 to a raised surface, it must perform positive work via concentric muscle 53 actions, in order to raise the COM (Buckley et al, 2008(Buckley et al, , 2011van Dieen 54 et al, 2007van Dieen 54 et al, , 2008. In both scenarios, the lead limb must be able to safely 55 support bodyweight whilst providing propulsion in the context of ongo-56 ing gait and avoiding contact with the step.…”

“…Although stepping gait may be executed by young able-bodied indi-58 viduals without apparent difficulty (Barbieri et al, 2013;Begg and 59 Sparrow, 2000;Buckley et al, 2011;van Dieen et al, 2007van Dieen et al, , 2008, it is 60 more mechanically challenging compared to level gait (Nadeau et al, 61 2003 (Aldridge et al, 2012;Alimusaj et al, 2009;Jones et al, 73 2006; Powers et al, 1997;Ramstrand and Nilsson, 2009;Schmalz 74 et al, 2007;Vanicek et al, 2010;Winter and Sienko, 1988). When…”