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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 itTimmis, Matthew A., Buckley, John 13 February 2012 (has links)
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.
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Utility of Peripheral Visual Cues in Planning and Controlling Adaptive GaitGraci, Valentina, Elliott, David, Buckley, John 01 1900 (has links)
No / The purpose of this article is to determine the relative importance to adaptive locomotion of peripheral visual cues provided by different parts of the visual field.
Twelve subjects completed obstacle crossing trials while wearing goggles that provided four visual conditions: upper visual field occlusion, lower visual field occlusion (LO), circumferential peripheral visual field occlusion (CPO), and full vision. The obstacle was either positioned as a lone structure or within a doorframe.
Given that subjects completed the task safely without cues from the lower or peripheral visual field, this suggests that subjects used exteroceptive information provided in a feed-forward manner under these conditions. LO and CPO led to increased foot placement distance from the obstacle and to increased toe clearance over the obstacle with a reduced crossing-walking velocity. The increased variability of dependent measures under LO and CPO suggests that exproprioceptive information from the peripheral visual field is generally used to provide online control of lower limbs. The presence of the doorframe facilitated lead-foot placement under LO by providing exproprioceptive cues in the upper visual field. However, under CPO conditions, the doorframe led to a further reduction in crossing velocity and increase in trail-foot horizontal distance and lead-toe clearance, which may have been because of concerns about hitting the doorframe with the head and/or upper body.
Our findings suggest that exteroceptive cues are provided by the central visual field and are used in a feed-forward manner to plan the gait adaptations required to safely negotiate an obstacle, whereas exproprioceptive information is provided by the peripheral visual field and used online to “fine tune” adaptive gait. The loss of the upper and lower peripheral visual fields together had a greater effect on adaptive gait compared with the loss of the lower visual field alone, likely because of the absence of lamellar flow visual cues used to control egomotion.
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Peripheral visual cues affect minimum-foot-clearance during overground locomotionGraci, Valentina, Elliott, David, Buckley, John 2009 July 1922 (has links)
No / The importance of peripheral visual cues in the control of minimum-foot-clearance during overground
locomotion on a clear path was investigated. Eleven subjects walked at their natural speed whilst
wearing goggles providing four different visual conditions: upper occlusion, lower occlusion,
circumferential–peripheral occlusion and full vision. Results showed that under circumferential–
peripheral occlusion, subjects were more cautious and increased minimum-foot-clearance and
decreased walking speed and step length. The minimum-foot-clearance increase can be interpreted
as a motor control strategy aiming to safely clear the ground when online visual exproprioceptive cues
from the body are not available. The lack of minimum-foot-clearance increase in lower occlusion
suggests that the view of a clear pathway from beyond two steps combined with visual exproprioception
and optic flow in the upper field were adequate to guide gait. A suggested accompanying safety strategy
of reducing the amount of variability of minimum-foot-clearance under circumferential–peripheral
occlusion conditions was not found, likely due to the lack of online visual exproprioceptive cues provided
by the peripheral visual field for fine-tuning foot trajectory.
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The role of peripheral visual cues in planning and controlling movement : an investigation of which cues provided by different parts of the visual field influence the execution of movement and how they work to control upper and lower limb motionGraci, Valentina January 2010 (has links)
Visual cues have previously been classified as visual exproprioceptive, when defining the relative position of the body within the environment and are continuously updated while moving (online), and visual exteroceptive when describing static features of the environment which are typically elaborated offline (feedforward). However peripheral visual cues involved in the control of movement have not previously been clearly defined using this classification. Hence the role played by peripheral visual cues in the planning and/or online control of movement remains unclear. The aim of this thesis was to provide a systematic understanding of the importance of peripheral visual cues in several types of movement, namely overground locomotion, adaptive gait, postural stability and reaching and grasping. 3D motion capture techniques were used to collect limb and whole body kinematics during such movements. Visual peripheral cues were manipulated by visual field occlusion conditions or by the employment of point-lights in a dark room. Results showed that the visual cues provided by different parts of the peripheral visual field are mainly used for online fine tuning of limb trajectory towards a target (either a floor-based obstacle or an object to grasp). The absence of peripheral visual cues while moving disrupted the spatio-temporal dynamic relationship between subject and target and resulted in increased margins of safety between body and target and increased time and variability of several dependent measures. These findings argue in favour of the classification of peripheral visual cues as visual exproprioceptive.
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The role of peripheral visual cues in planning and controlling movement :|ban investigation of which cues provided by different parts of the visual field influence the execution of movement and how they work to control upper and lower limb motion.Graci, Valentina January 2010 (has links)
Visual cues have previously been classified as visual exproprioceptive, when defining the relative position of the body within the environment and are continuously updated while moving (online), and visual exteroceptive when describing static features of the environment which are typically elaborated offline (feedforward). However peripheral visual cues involved in the control of movement have not previously been clearly defined
using this classification. Hence the role played by peripheral visual cues in the planning and/or online control of movement remains unclear.
The aim of this thesis was to provide a systematic understanding of the importance of peripheral visual cues in several types of movement, namely overground locomotion, adaptive gait, postural stability and reaching and grasping.
3D motion capture techniques were used to collect limb and whole body kinematics during such movements. Visual peripheral cues were manipulated by visual field occlusion conditions or by the employment of point-lights in a dark room.
Results showed that the visual cues provided by different parts of the peripheral visual field are mainly used for online fine tuning of limb trajectory towards a target (either a floor-based obstacle or an object to grasp). The absence of peripheral visual cues while moving disrupted the spatio-temporal dynamic relationship between subject and target and resulted in increased margins of safety between body and target and increased time and variability of several dependent measures. These findings argue in favour of the classification of peripheral visual cues as visual exproprioceptive.
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