Yes / 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, footplacement 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.

No / We often complete step downs in the absence of visual feedback of the lower-limbs, and/or of the area on the ground where we intend to land (e.g. when descending a step whilst carrying a laundry basket). Therefore, the present study examined whether information from lower visual field (lvf) provides any advantage to the control of step descent. Ten healthy subjects (age 24.4 ± 9.4 years) completed repeated step downs over three-step heights with visual information available from either full or upper visual fields (lvf occluded), and for specific intervals relative to step initiation. Visuomotor control of step descent was assessed by determining pre-landing kinematic measures and landing mechanic variables for the initial landing period. Findings indicate that whilst there were only limited effects on pre-landing kinematic measures under lvf occlusion, individual’s ability to plan/control landing mechanics was significantly different in such conditions compared to when they had access to full field vision. These changes were consistent with participants being uncertain regarding precise floor height when access to lvf was restricted, and consequently led them to adapt their landing behaviour but without fundamentally altering their stepping strategy. Compared to when vision was available throughout, the occlusion of vision (full or upper visual field) from toe-off or mid-swing onwards caused very few differences in landing behaviour. This suggests that the contribution of information from lvf to the control of landing behaviour occurs predominantly prior to or during movement initiation and that ‘online’ vision is used only in the latter portion of the descent phase to subtly ‘fine tune’ landings.

The majority of previous research investigating the role of vision in controlling adaptive gait has predominantly focused on over-ground walking or obstacle negotiation. Thus there is a paucity of literature investigating visuomotor control of step descent. This thesis addressed the importance of the lower visual field (lvf) in regulating step descent landing control, and determined when visual feedback is typically used in regulating landing control prior to/during step descent. When step descents were completed from a stationary starting position, with the lvf occluded or degraded, participants adapted their stepping strategy in a manner consistent with being uncertain regarding the precise location of the foot/lower leg relative to the floor. However, these changes in landing control under conditions of lvf occlusion were made without fundamentally altering stepping strategy. This suggests that participants were able to plan the general stepping strategy when only upper visual field cues were available. When lvf was occluded from either 2 or 1 step(s) prior to descending a step during on-going gait, stepping strategy was only affected when the lvf was occluded in the penultimate step. Findings suggest that lvf cues are acquired in the penultimate step/few seconds prior to descent and provide exproprioceptive information of the foot/lower leg relative to the floor which ensures landing is regulated with increased certainty. Findings also highlight the subtle role of online vision used in the latter portion of step descent to 'fine tune' landing control.

The majority of previous research investigating the role of vision in controlling adaptive gait has predominantly focused on over-ground walking or obstacle negotiation. Thus there is a paucity of literature investigating visuomotor control of step descent. This thesis addressed the importance of the lower visual field (lvf) in regulating step descent landing control, and determined when visual feedback is typically used in regulating landing control prior to / during step descent. When step descents were completed from a stationary starting position, with the lvf occluded or degraded, participants adapted their stepping strategy in a manner consistent with being uncertain regarding the precise location of the foot / lower leg relative to the floor. However, these changes in landing control under conditions of lvf occlusion were made without fundamentally altering stepping strategy. This suggests that participants were able to plan the general stepping strategy when only upper visual field cues were available. When lvf was occluded from either 2 or 1 step(s) prior to descending a step during on-going gait, stepping strategy was only affected when the lvf was occluded in the penultimate step. Findings suggest that lvf cues are acquired in the penultimate step / few seconds prior to descent and provide exproprioceptive information of the foot / lower leg relative to the floor which ensures landing is regulated with increased certainty. Findings also highlight the subtle role of online vision used in the latter portion of step descent to 'fine tune' landing control.