Humans exploit the biomechanics of bipedal gait during visually guided walking over complex terrain

Matthis, Jonathan; Fajen, Brett R.

doi:10.1098/rspb.2013.0700

Cited by 67 publications

(80 citation statements)

References 48 publications

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“…Thus, subjects were able to maintain stepping accuracy in this condition but only by trading off on walking speed. This trade-off is consistent with behavior observed while attempting to avoid stepping on obstacles under analogous visibility constraints (43,44).…”

Section: ])supporting

confidence: 83%

“…Although the findings of Matthis and Fajen (43,44) and Matthis, Barton, and Fajen (46) are consistent with the critical control phase hypothesis, they are not sufficient to conclude that visual information is primarily used during the latter part of the preceding step because the two components of the critical phase hypothesis were tested in separate experiments. The first aim of this study was to provide a direct test by combining the manipulations used in the previous studies in a single experimental task.…”

Section: Resultsmentioning

confidence: 82%

“…Thus, the 1.5 trigger used in the Just in Time condition provided subjects with two step lengths of visual look ahead. Put another way, the 1.5 trigger in this study is equivalent to the two step-length visibility windows used in Matthis and Fajen (43,44).…”

Section: Methodsmentioning

confidence: 99%

“…‡ Indeed, restricting a walker's ability to see upcoming terrain to less than two step lengths results in decreases in stepping accuracy and walking speed (43). Furthermore, the trajectory of the COM is less like that of a passively moving inverted pendulum compared with when walkers can see two or more step lengths ahead, suggesting that walkers need at least two step lengths of visual lookahead to exploit their inverted pendulum dynamics when walking over complex terrain (44). Interestingly, these findings converge with studies of gaze behavior that demonstrate that walkers tend to look about two steps ahead when walking over complex terrain (32).…”

Section: The Critical Control Phase Hypothesismentioning

confidence: 99%

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The critical phase for visual control of human walking over complex terrain

Matthis

Barton

Fajen

2017

Proc. Natl. Acad. Sci. U.S.A.

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104

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To walk efficiently over complex terrain, humans must use vision to tailor their gait to the upcoming ground surface without interfering with the exploitation of passive mechanical forces. We propose that walkers use visual information to initialize the mechanical state of the body before the beginning of each step so the resulting ballistic trajectory of the walker's center-of-mass will facilitate stepping on target footholds. Using a precision stepping task and synchronizing target visibility to the gait cycle, we empirically validated two predictions derived from this strategy: (1) Walkers must have information about upcoming footholds during the second half of the preceding step, and (2) foot placement is guided by information about the position of the target foothold relative to the preceding base of support. We conclude that active and passive modes of control work synergistically to allow walkers to negotiate complex terrain with efficiency, stability, and precision.H umans and other animals are remarkable in their ability to take advantage of what is freely available in the environment to the benefit of efficiency, stability, and coordination in movement. This opportunism can take on at least two forms, both of which are evident in human locomotion over complex terrain: (i) harnessing external forces to minimize the need for self-generated (i.e., muscular) forces (1), and (ii) taking advantage of passive stability to simplify the control of a complex movement (e.g., ref. 2). In the ensuing section, we explain how walkers exploit external forces and passive stability while walking over flat, obstacle-free terrain.* We then generalize this account to walking over irregular surfaces by explaining how walkers can adapt gait to terrain variations while still reaping the benefits of the available mechanical forces and inherent stability. This account leads to hypotheses about how and when walkers use visual information about the upcoming terrain and where that information is found. We derive several predictions from these hypotheses and then put them to the test in three experiments. Passive Control in Human WalkingThe basic movement pattern of the human gait cycle arises primarily from the phasic activation of flexor and extensor muscle groups by spinal-level central pattern generators, regulated by sensory signals from lower limb proprioceptors and cutaneous feedback from the plantar surface of the foot. This low-level neuromuscular circuitry serves to maintain the rhythmic physical oscillations that define locomotor behavior (see ref. 3 for review). This section will provide an overview of the basic biomechanics of the bipedal gait cycle to show how these inherent physical dynamics contribute to the passive stability and energetic efficiency of human locomotion.During the single support phase of the bipedal gait cycle, when only one foot is in contact with the ground, a walker shares the physical dynamics of an inverted pendulum. The body's center of mass (COM) acts as the bob of the pendulum and is support...

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Section: ])supporting

confidence: 83%

Section: Resultsmentioning

confidence: 82%

Section: Methodsmentioning

confidence: 99%

Section: The Critical Control Phase Hypothesismentioning

confidence: 99%

See 2 more Smart Citations

The critical phase for visual control of human walking over complex terrain

Matthis

Barton

Fajen

2017

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

104

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“…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).…”

Section: Vision and Stabilitymentioning

confidence: 99%

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

Birn-Jeffery

Higham

2016

Journal of Experimental Biology

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Locomotion through complex habitats relies on the continuous feedback from a number of sensory systems, including vision. Animals face a visual trade-off between acuity and light sensitivity that depends on light levels, which will dramatically impact the ability to process information and move quickly through a habitat, making ambient illumination an incredibly important ecological factor. Despite this, there is a paucity of data examining ambient light in the context of locomotor dynamics. There have been several independent transitions from the nocturnal ancestor to a diurnal activity pattern among geckos. We examined how ambient light level impacted the locomotor performance and high-speed three-dimensional kinematics of a secondarily diurnal, and cursorial, gecko (Rhoptropus afer) from Namibia. This species is active under foggy and sunny conditions, indicating that a range of ambient light conditions is experienced naturally. Locomotor speed was lowest in the 'no-light' condition compared with all other light intensities, occurring via a combination of shorter stride length and lower stride frequency. Additionally, the centre of mass was significantly lower, and the geckos were more sprawled, in the no-light condition relative to all of the higher light intensities. Locomotor behaviour is clearly sub-optimal under lower light conditions, suggesting that ecological conditions, such as very dense fog, might preclude the ability to run quickly during predator-prey interactions. The impact of ambient light on fitness should be explored further, especially in those groups that exhibit multiple transitions between diel activity patterns.

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