Obstacle crossing during locomotion: Visual exproprioceptive information is used in an online mode to update foot placement before the obstacle but not swing trajectory over it

Abstract

Although gaze during adaptive gait involving obstacle crossing is typically directed two or more steps ahead, visual information of the swinging lower-limb and its relative position in the environment (termed visual exproprioception) is available in the lower visual field (lvf). This study determined exactly when lvf exproprioceptive information is utilised to control/update lead-limb swing trajectory during obstacle negotiation. 12 young participants negotiated an obstacle wearing smart-glass goggles which unpredictably occluded the lvf for certain periods during obstacle approach and crossing. Trials were also completed with lvf occluded for the entirety of the trial. When lvf was occluded throughout, foot-placement distance and toe-clearance became significantly increased; which is consistent with previous work that likewise used continuous lvf occlusion. Both variables were similarly affected by lvf occlusion from instant of penultimate-step contact, but both were unaffected when lvf was occluded from instant of final-step contact. These findings suggest that lvf (exproprioceptive) input is typically used in an online manner to control/update final foot-placement, and that without such control, uncertainty regarding foot placement causes toe-clearance to be increased. Also that lvf input is not normally exploited in an online manner to update toe-clearance during crossing: which is contrary to what previous research has suggested.

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).…”

Restricting ankle motion via orthotic bracing reduces toe clearance when walking over obstacles

“…Obstacle clearance has been reported as the distance between the obstacle and the toe or the obstacle and the heel, as these parts of the foot are nearest to the obstacle during crossing [4,13,[19][20][21]. For this reason, the current study takes both clearances into consideration as well as foot placement parameters (i.e.…”

Light level impacts locomotor biomechanics in a secondarily diurnal gecko,Rhoptropus afer

“…Knowledge of the height of ground contact is an important input for locomotor control, which is often provided via visual feedback information. When visual information regarding ground contact is not available, adjustments to ground clearance are made to increase the 'safety factor' (Matthis and Fajen, 2014;Timmis and Buckley, 2012), although there is a minimum level of visual information below which falls are highly likely (Matthis and Fajen, 2013).…”

“…Visual feedback information also alters locomotor strategies when moving in non-level environments. For example, the lower visual field adjusts movement and foot placements (Buckley et al, 2011;Marigold and Patla, 2008;Timmis et al, 2009;Timmis and Buckley, 2012), loss of visual information results in poorer upper body stability (Iosa et al, 2012;Logan et al, 2010) and reduction in visual field causes humans to use less efficient but safer strategies (Jansen et al, 2011). Although we are gaining a greater understanding of the integration of the two systems in humans, we still do not know whether these are applicable to other terrestrial animals that deal with far rougher terrain and the requirement for better capture or escape responses.…”