The Effect of Perceived Locomotor Constraints on Distance Estimation

Two experiments were conducted to examine the ways in which the visual estimation of distance to a target is affected by constraints perceived to be placed on the subsequent locomotion to the target without vision. We hypothesized that an appraisal of impending effort would play a role in ascertaining the distance to be walked. In Experiment 1, the amount of resistance to walking was variable and unpredictable. One group of subjects performed against relatively low resistance, whereas another group performed against substantially greater resistance. In the low-resistance condition, no significant differences in CE, VE, time to target, or number of steps to target were found between any of the eight combinations of predictable or unpredictable resistances during walking. In the high-resistance condition, however, significant differences were found for CE and number of strides to target when resistance varied unpredictably during walking. Experiment 2 was similar in design but required subjects to walk with combinations of normal or short steps after they had viewed the target knowing only the gait type that would be used to begin locomotion. No differences in CE, VE, or time to target were found between four different combinations of gait type and predictability, under subjectively controlled conditions. When the step constraints were externally imposed, however, differences were found for CE. None of the results from either experiment, in which the number of strides needed to reach the target or the predictability of gait did not change from normal, supported the hypothesis that motor output requirements are necessary in forming a mental representation of the target position that can be used to walk to the target with eyes closed. Whichever locomotor technique was used to walk the estimated distance in these cases, the representation was able to be used independently. When walking mechanics were altered by externally imposed constraints, however, the success at reaching the estimated target position was reduced. These latter results are consistent with those obtained using up, down, and level walking and support the premise that mental representations used in blind walking are linked to the locomotor mechanics afforded by environmental conditions.     

On-Line Updating of Spatial Information Druing Locomotion Without Vision

Two experiments are reported in which the control of locomotion without vision was investigated. In Experiment 1, subjects (N = 10) made similar, although less functional, locomotor adjustments when walking without vision to a target than they did when walking with vision. That result suggests that while walking without vision, the subjects updated their positions on-line with respect to a representation of the target rather than operating from a preformulated action plan. In Experiment 2, there was a significant weakening and loss of functionality of the locomotor adjustments when subjects (N = 10) had to walk without vision the correct distance to the target but in a direction opposite to its true location, as compared with when they walked without vision directly to the target. That finding suggests that the subjects were nonvisually updating their positions not with respect to an abstract representation of the target's distance but with respect to a representation of its relative location within the task environment.     

The organization of exploratory behaviors in infant locomotor planning

How do infants plan and guide locomotion under challenging conditions? This experiment investigated the real‐time process of visual and haptic exploration in 14‐month‐old infants as they decided whether and how to walk over challenging terrain – a series of bridges varying in width. Infants’ direction of gaze was recorded with a head‐mounted eye tracker and their haptic exploration and locomotor actions were captured on video. Infants’ exploration was an organized, efficient sequence of visual, haptic, and locomotor behaviors. They used visual exploration from a distance as an initial assessment on nearly every bridge. Visual information subsequently prompted gait modifications while approaching narrow bridges and haptic exploration at the edge of the bridge. Results confirm predictions about the sequential, ramping‐up process of exploration and the distinct roles of vision and touch. Exploration, however, was not a guarantee of adaptive decisions. With walking experience, exploratory behaviors became increasingly efficient and infants were better able to interpret the resulting perceptual information in terms of whether it was safe to walk.     

Locomotor estimation of distance after visual scanning by children and adults

Subjects (120 young adults and 120 children) were tested for their abilities to estimate visually the distance to a target 5 m away, then walk unaided by vision to that target as accurately as possible. Experimental groups were determined by visual scanning time (1, 5, or 10 s), delay between the end of visual scanning and the start of locomotion (0, 1, 3, or 5 s), and by age (9 year old children or young adult). Adults performed locomotor distance estimations based on visual scanning more accurately than children under all conditions. Increased scanning time resulted in more accurate performances by children but not by adults, and increased delays between the end of scanning and the start of locomotion caused decreases in accuracy for children only. These decrements were partially ameliorated by increased scanning time. The total time spent without vision after scanning the target (delay time plus walking time) was an important factor, with sharp increases in error for all delay conditions for children. The results are discussed in terms of trace decay effects and developmental aspects of visual guidance of locomotion.     

A comparison of visual and nonvisual sensory inputs to walked distance in a blind-walking task

Two experiments were conducted in order to assess the contribution of locomotor information to estimates of egocentric distance in a walking task. In the first experiment, participants were either shown, or led blind to, a target located at a distance ranging from 4 to 10 m and were then asked to indicate the distance to the target by walking to the location previously occupied by the target. Participants in both the visual and locomotor conditions were very accurate in this task and there was no significant difference between conditions. In the second experiment, a cue-conflict paradigm was used in which, without the knowledge of the participants, the visual and locomotor targets (the targets they were asked to walk to) were at two different distances. Most participants did not notice the conflict, but despite this their responses showed evidence that they had averaged the visual and locomotor inputs to arrive at a walked estimate of distance. Together, these experiments demonstrate that, although they showed poor awareness of their position in space without vision, in some conditions participants were able to use such nonvisual information to arrive at distance estimates as accurate as those given by vision.     

Overground gait training using virtual reality aimed at gait symmetry

This study investigated if training in a virtual reality (VR) environment that provides visual and audio biofeedback on foot placement can induce changes to spatial and temporal parameters of gait during overground walking. Eighteen healthy young adults walked for 23 min back and forth on an instrumented walkway in three different conditions: (i) real environment (RE), (ii) virtual environment (VE) with no biofeedback, and (iii) VE with biofeedback. Visual and audio biofeedback while stepping on virtual footprint targets appearing along a straight path encouraged participants to walk with an asymmetrical step length (SL). A repeated-measures, one-way ANOVA, followed by a pairwise comparison post-hoc analysis with Bonferroni's correction, was performed to compare the step length difference (SLD), stance phase percentage difference (SPPD), and double-support percentage difference (DSPD) between early and late phases of all walking conditions. The results demonstrate the efficacy of the VE biofeedback system for training asymmetrical gait patterns. Participants temporarily adapted an asymmetrical gait pattern immediately post-training in the VE. Induced asymmetries persisted significantly while later walking in the RE. Asymmetry was significant in the spatial parameters of gait (SLD) but not in the temporal parameters (SPPD and DSPD). This paper demonstrates a method to induce unilateral changes in spatial parameters of gait using a novel VR tool. This study provides a proof-of-concept validation that VR biofeedback training can be conducted directly overground and could potentially provide a new method for treatment of hemiplegic gait or asymmetrical walking.     

Gait dynamics, fractals and falls: finding meaning in the stride-to-stride fluctuations of human walking

Until recently, quantitative studies of walking have typically focused on properties of a typical or average stride, ignoring the stride-to-stride fluctuations and considering these fluctuations to be noise. Work over the past two decades has demonstrated, however, that the alleged noise actually conveys important information. The magnitude of the stride-to-stride fluctuations and their changes over time during a walk - gait dynamics - may be useful in understanding the physiology of gait, in quantifying age-related and pathologic alterations in the locomotor control system, and in augmenting objective measurement of mobility and functional status. Indeed, alterations in gait dynamics may help to determine disease severity, medication utility, and fall risk, and to objectively document improvements in response to therapeutic interventions, above and beyond what can be gleaned from measures based on the average, typical stride. This review discusses support for the idea that gait dynamics has meaning and may be useful in providing insight into the neural control of locomotion and for enhancing functional assessment of aging, chronic disease, and their impact on mobility.     

Effects of optic flow on the kinematics of human gait: a comparison of young and older adults

This experiment studied the effect of imposed optic flow on human locomotion. Six young and 6 older adults were exposed to various patterns of optic flow while walking in a moving hallway. Results showed few cases of impaired postural control (staggers, parachute reactions). No falls were recorded. Kinematic patterns of gait were altered when vision was absent or inconsistent optic flow was presented: Ninety two percent of the subjects' mean step velocity differed from their step velocities under normal vision. Compared with imposed central flow, peripheral optic flow was not dominant in inducing kinematic changes. Characteristic gait profiles were obtained, depending on flow direction. Global backward flow tended to slow down step velocity, whereas subjects' step velocity increased during conditions of forward flow. The results suggest that subjects attempted to match their own walking speed to the velocity of the moving visual scenes. It is concluded that in an uncluttered environment, imposed optic flow has a modulating rather than a destabilizing effect on human locomotion.     

Reproducibility of distance and direction errors associated with forward, backward, and sideway walking in the context of blind navigation

The ability to navigate without vision towards a previously seen target has been extensively studied, but its reliability over time has yet to be established. Our aims were to determine distance and direction errors made during blind navigation across four different directions involving three different gait patterns (stepping forward, stepping sideway, and stepping backward), and to establish the test-retest reproducibility of these errors. Twenty young healthy adults participated in two testing sessions separated by 7 days. They were shown targets located, respectively, 8 m ahead, 8 m behind, and 8 m to their right and left. With vision occluded by opaque goggles, they walked forward (target ahead), backward (target behind), and sideway (right and left targets) until they perceived to be on the target. Subjects were not provided with feedback about their performance. Walked distance, angular deviation, and body rotation were measured. The mean estimated distance error was similar across the four walking directions and ranged from 16 to 80 cm with respect to the 8 m target. In contrast, direction errors were significantly larger during sideway navigation (walking in the frontal plane: leftward, 10 degrees +/- 15 degrees deviation; rightward, 18 degrees +/- 13 degrees) than during forward and backward navigation (walking in the sagittal plane). In general, distance and direction errors were only moderately reproducible between the two sessions [intraclass correlation coefficients (ICCs) ranging from 0.682 to 0.705]. Among the four directions, rightward navigation showed the best reproducibility with ICCs ranging from 0.607 to 0.726, and backward navigation had the worst reliability with ICCs ranging from 0.094 to 0.554. These findings indicate that errors associated with blind navigation across different walking directions and involving different gait patterns are only moderately to poorly reproducible on repeated testing, especially for walking backward. The biomechanical constraints and increased cognitive loading imposed by changing the walking pattern to backward stepping may underlie the poor performance in this direction.     

Self-motion perception during locomotor recalibration: more than meets the eye

Do locomotor aftereffects depend specifically on visual feedback? In 7 experiments, 116 college students were tested, with closed eyes, at stationary running or at walking to a previewed target after adaptation, with closed eyes, to treadmill locomotion. Subjects showed faster inadvertent drift during stationary running and increased distance (overshoot) when walking to a target. Overshoot seemed to saturate (i.e., reach a ceiling) at 17% after as little as 1 min of adaptation. Sidestepping at test reduced overshoot, suggesting motor specificity. But inadvertent drift effects were decreased if the eyes were open and the treadmill was drawn through the environment during adaptation, indicating that these effects involve self-motion perception. Differences in expression of inadvertent drift and of overshoot after adaptation to treadmill locomotion may have been due to different sets of ancillary cues available for the 2 tasks. Self-motion perception is multimodal.     

Developmental trajectory of dynamic resource utilization during walking: toddlers with and without Down syndrome

After years of walking practice 8-10-year-old children with typical development (TD) and those with Down syndrome (DS) show uniquely different but efficient use of dynamic resources to walk overground and on a treadmill [Ulrich, B.D., Haehl, V., Buzzi, U., Kubo, M., & Holt, K.G. (2004). Modeling dynamic resource utilization in populations with unique constraints: Preadolescents with and without Down syndrome. Human Movement Science, 23, 133-156]. Here we examined the use of global stiffness and angular impulse when walking emerged and across the ensuing months of practice in eight toddlers with TD and eight with DS. Participants visited our lab when first able to walk four to six steps, and at one, three, four, and six months of walking experience. For all visits, toddlers walked overground at their preferred speeds and for the last two visits on a treadmill. Toddlers with TD and DS demonstrated clear and similar developmental trajectories over this period with more similarities than differences between groups. At six months stiffness and impulse values were higher than previously observed for 8-10-year-old children. Stiffness values increased significantly throughout this period, though rate of change slowed for the TD group by three months of experience. Impulse values rose sharply initially and slowed to plateau during the latter months. Treadmill data illustrated toddlers' capacity to adapt dynamic resource use to imposed changes in speed, particularly well after six months of practice. Consistent with our studies of preadolescents and older adults, toddlers with DS produced significantly wider normalized step width than their TD peers. We propose that the challenge of upright bipedal locomotion constrains toddlers with TD and DS to generate similar, necessary and sufficient stiffness and impulse values to walk as they gain control and adapt to playful and self-imposed perturbations of gait over the first six months. The plateau in impulse and slow-down of stiffness increases over the latter months may be the first signs of a downward trend to the lower values produced by older children with several years of walking experience.     

How is gait visually regulated when the head is travelling faster than the legs?

Gait regulation patterns were examined under various visual conditions in order to determine whether speed information provided by peripheral vision is taken into account in gait adjustments. Nine subjects walking toward a visual target on the ground were required to place one foot exactly on it. peripheral vision was either restricted to a 12 degrees angle or decorrelated, corresponding to a moving speed greater than the actual walking speed. Decorrelation was obtained by placing the subject on a treadmill moving in the walking direction. The results show, by comparison with the control condition, that the restriction of peripheral visual information did not affect the accuracy of the foot positioning, whereas decorrelated conditions affected it significantly: we noted that the gait regulation was triggered early on and showed a very stable pattern so that the distance to the target was consistently underestimated. This suggest that, although visual speed information is not indispensable in this kind of task, it is nevertheless taken into account in stride adjustments when the whole visual field is available. The results are discussed, in the context of a time-based approach to locomotor activity, in relation to the possible visual methods that might be used in obtaining information about time to contact the target.     

The influence of walking speed and prior practice on locomotor distance estimation

In an attempt to reconcile discrepant findings in the literature (Elliott, 1986; Thomson, 1983), walking speed, prior practice, and walking delay were manipulated to determine if they had an impact on locomotor distance estimation. Contrary to suggestions by Thomson (1986), walking variability in the direction of locomotion depended only on a subject' initial distance from the targets.     

The Influence of Walking Speed and Prior Practice on Locomotor Distance Estimation

In an attempt to reconcile discrepant findings in the literature (Elliott, 1986; Thomson, 1983), walking speed, prior practice, and walking delay were manipulated to determine if they had an impact on locomotor distance estimation. Contrary to suggestions by Thomson (1986), walking variability in the direction of locomotion depended only on a subject’s initial distance from the targets.     

Walking and periventricular leukomalacia: locomotor characteristics and brain imaging (MRI)

The aim of the present study was to compare the walking abilities in infants with and without periventricular leukomalacia and to see whether the severity of the brain damage was related to locomotor outcome of the infants at 12 and 18 months. 47 newborns were included in the study based on white matter abnormalities on ultrasound. Magnetic resonance imaging (MRI) recordings during the neonatal period were used to identify and quantify the location and severity of the brain lesions. Locomotor outcome was assessed in terms of disability at 12 and 18 months. The quality of walking, including global and segmental gait parameters, was measured for the infants who could walk independently at 18 months and compared to a group of healthy control infants. The number of children who could walk was related to the extent of white matter abnormalities seen on the neonatal MRI, but the quality of walking was not.     

Dominance of gait cycle duration in casual walking

In gait research, casual walking has been considered to be walking at a casual speed. However, it is unclear that walking speed is the most stable factor in casual walking compared to other factors such as cycle duration and stride length. Although walking speed can be calculated from cycle duration and stride length, it is not necessarily the case that these parameters are "stable" in the same manner. We therefore conducted an experiment to determine which of these three parameters is most stable, regarding walking speed as cycle speed and using the coefficient of variation across gait cycles as index of stability. Ten participants were invited to walk in their own casual manner, once a week for a period of four weeks. Cycle duration was measured by means of a foot switch attached to the right heel. To measure the moving distance, participants towed a distance meter. Stride length and cycle speed were measured using this device. Over the four-week period, cycle duration and stride length were stable, whereas cycle speed was the most variable parameter. Furthermore, in the results for each single day, the cycle duration was significantly more stable than the other parameters. These results suggest that, when we walk casually, cycle duration is the dominant factor, rather than stride length or walking speed.     

Occlusion of the lower visual field when wearing a facial mask does not compromise gait control when stepping into a hole in older adults

Visual exproprioception obtained from the lower visual field (LVF) is used to control locomotion on uneven terrain. Wearing a facial mask obstructs the LVF and can compromise gait control. Therefore, this study aimed to investigate the effect of occluding the LVF when wearing a facial mask on gait control while walking and stepping into a hole in older adults. Fifteen older adults walked along a wooden walkway under two different surface conditions (without and with a hole [60 cm wide and long, with a depth of 9.5 cm] and three visual conditions (control, mask, and basketball goggles with an occluded LVF). We found that occlusion of the LVF with masks or goggles did not affect the adaptations necessary to step into a hole. Neither behavioral (gait speed, margin of stability, foot landing position) nor neuromuscular (EMG activation and co-activation) parameters were affected by either visual manipulation. Older adults used a downward head pitch strategy to compensate for visual obstruction and plan the anticipatory adjustments to step into the hole. The absence of lower limb visual exproprioception due to wearing a mask did not affect locomotion control when stepping into a hole in older adults. Older adults compensated for the obstruction of the LVF through head downward tilt, which allowed them to obtain visual information about the hole two steps ahead to make anticipatory locomotor adjustments.     

Effects of gait pattern and arm swing on intergirdle coordination

Mature locomotion in humans is characterized by an anti-phase coordination (moving in opposite directions) between the pelvic and the scapular girdles. This pattern involves a specific relationship between the arm and leg motion is deemed to be most flexible and dynamically efficient. Still, when the arms are involved in another task, like a field player running with a ball in the hands, locomotion is still possible. In order to probe the flexibility of the locomotor synergy, the present study aimed to determine the persistence and the strength of the coordination patterns between the pelvic and scapular girdles when no arm swing was allowed during walking and running. Relative phase, the time difference between the girdle rotations, measured the ongoing inter-girdle coordination of eight healthy participants asked to walk and run with or without arm swing. Results showed that an absence of arm swing led to a change from an anti-phase to in-phase pattern (girdles moving in the same direction) and that an increase in velocity strengthened the adopted pattern. Moreover, the frequency distribution of relative phase for all gait patterns with arm swing proved to be bimodal, indicating that the prevailing anti-phase pattern was always mixed with a noticeable proportion of in-phase coordination. The presence of the in-phase pattern in the easy, natural locomotion with arm swing manifests its persistence and its stability, perhaps pertaining to its prevalence in earlier times in ontogeny or evolution.     

Visual perception and the guidance of locomotion without vision to previously seen targets

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.