Postural requirements and progression velocity in young walkers

This article describes developmental changes in gait velocity and relates these changes to gait parameters that index postural stability (step width and lateral acceleration) and two components of velocity (cadence and step length). Five children were observed longitudinally over a 2-year period after onset of independent walking. Their range of speed increased threefold in the first 6 months of independent walking and then remained constant. In contrast, step width decreased approximately twofold. Whereas in adults, cadence and step length contribute approximately equally to speed, when infants first begin to walk independently, increase in velocity is due mostly to increased step length. After 5 months of independent walking, the pattern reverses, and increase in velocity is due primarily to increased cadence. The pattern remains constant over the next 18 months. From a developmental point of view, the data lead us to interpret early walking (the first 5 months) as a process of integration of postural constraints into the dynamic necessities of gait movement. A second phase, beginning after 4 to 5 months of independent walking, is considered to be a tuning phase characterized by a more precise adjustment of the gait parameters.     

Detection of the relevant type of locomotion in infancy: crawlers versus walkers

Human infants show a preference for individuals who are similar to them. Using point-light displays of human walkers and crawlers as stimuli, we examined whether infants' preference for the motions of crawling and walking changes between, before, and after the onset of bipedal walking. The results show that crawling and walking infants prefer the types of locomotion that are similar to their own, respectively. These indicate that the infants detect the similarities between the motions they performed and they observed, which provides the behavioral evidence that the production of a particular motion is connected to its perception in infancy.     

Flow structure versus retinal location in the optical control of stance

In four experiments I examined the importance of the retinal center and periphery in the pickup of optical information for controlling stance as a function of the dynamic geometrical structure of the optical flow. All experiments were performed in a moving room so that the magnitude of compensatory sway in response to room movements could be measured. In Experiments 1 and 2 I found stronger sway response to flow having a largely lamellar structure that was presented to the retinal periphery than to more radially structured flow in the center. In Experiment 3 observers turned their heads to face the right wall of the room, placing radial flow in the periphery and lamellar flow in the center of the visual field. Radial flow presented to the retinal periphery induced no compensatory sway. Lamellar flow in the center of the retina produced some sway. Flow structure apparently interacts with the exposed retinal area in controlling stance.     

Mathematical models of central pattern generators in locomotion: II. Single limb models for locomotion in the cat

Three mathematical models of central pattern generation for locomotion in the single limb of the cat are presented. In each model, the activities in populations of neurons controlling limb joint flexors and extensors are described by a system of nonlinear differential equations. Each solution of the system for a different set of parameters corresponds to a simulation of some gait of the cat. Model I is based on unit generators for each limb joint muscle group and assumes that flexors inhibit their paired extensors, but not vice-versa. Model IIa assumes that flexors and extensors are mutually inhibitory, but that only the flexors have inherent oscillatory capability. Model IIb assumes flexors and extensors are mutually inhibitory and that both flexors and extensors have oscillatory capability. The properties of each of these models are explored, compared and contrasted, and discussed in relation to the experimental literature. All three models are shown to be capable of generating patterns consistent with various stepping rates of the cat and to show appropriate muscle sequencing and flexor-extensor interactions. Further, all three models exhibit smooth initiation and termination of stepping. However, Model I seems to provide a more parsimonious account of producing changes in stepping rate and is preferred, therefore, over models IIa and IIb.     

Analysis of the transition from upright stance to steady state locomotion in children with under 200 days of autonomous walking

The aim of this paper was to study, from a developmental perspective, the transient phase of gait during the period between the standing posture and the achievement of steady state gait, using temporal and biochemical parameters. Eight children who had been walking autonomously for 90 to 200 days were observed. A total of 64 sequences of steps were analyzed. A sequence of steps began with the child standing still and was executed on a large force plate. From the determination of the instantaneous velocity of center of gravity results establish that, unlike adults, progression velocity in children end of the first step, but after two to four steps.The gait initiation process does not depend on the steady state velocity, but results from an initial fall. The duration of the movement up to the end of the first step is independent of the progression velocity but depends only upon the body mass and moment of inertia of the children.     

The influence of visual flow and perceptual load on locomotion speed

Visual flow is used to perceive and regulate movement speed during locomotion. We assessed the extent to which variation in flow from the ground plane, arising from static visual textures, influences locomotion speed under conditions of concurrent perceptual load. In two experiments, participants walked over a 12-m projected walkway that consisted of stripes that were oriented orthogonal to the walking direction. In the critical conditions, the frequency of the stripes increased or decreased. We observed small, but consistent effects on walking speed, so that participants were walking slower when the frequency increased compared to when the frequency decreased. This basic effect suggests that participants interpreted the change in visual flow in these conditions as at least partly due to a change in their own movement speed, and counteracted such a change by speeding up or slowing down. Critically, these effects were magnified under conditions of low perceptual load and a locus of attention near the ground plane. Our findings suggest that the contribution of vision in the control of ongoing locomotion is relatively fluid and dependent on ongoing perceptual (and perhaps more generally cognitive) task demands.     

Mathematical models of central pattern generators in locomotion: I. Current problems

As a background for subsequent studies of mathematical models of central pattern generators in locomotion (Stafford & Barnwell, 1985a, b) relevant aspects of the literature on locomotion are reviewed, concepts of locomotion discussed, and extant models considered. Advantages and disadvantages of present models are discussed, and the need for mathematical models is emphasized. It is shown that realistic models of pattern generation in locomotion must take numerous factors into account, including phases of step cycle, muscle sequencing, gait and interlimb coordination, initiation and cessation of locomotion, and many aspects of neuromuscular control and function.     

Use of a standard cane increases unipedal stance time during static testing

The records of 11 consecutive qualifying patients were reviewed to evaluate whether use of a cane increased unipedal balance time during static testing. Measured with a stopwatch, the maximum unipedal balance time increased significantly with use of a single-point cane, whether standing on the left (M = 14.4 sec.) or right (M = 16.7 sec.) lower limb. The results indicate that in clinical situations, sophisticated instruments are not needed to demonstrate the effects of a cane and that unipedal stance times obtained with a stopwatch can confirm the effectiveness of canes for increasing unipedal balance of patients and caregivers.     

Use of landmarks and allocentric reference frames for the control of locomotion

In the present study we assessed the use of landmarks and scene layout information for the control of locomotion. Observers were presented displays simulating forward locomotion through a random dot field with the horizontal position perturbed by a sum-of-sines function and were asked to steer and null out the horizontal disturbance of the path of locomotion. The results indicate greater control gain and accuracy when presented with a repeating layout of landmarks as compared to a changing layout of landmarks. Debriefing responses suggest that observers may have implicitly learned the layout of the repeating pattern. These results suggest that observers use an allocentric representation of the scene for steering control. A model for the control of locomotion is discussed that utilizes both scene-based information and optic flow.     

Social suggestibility to central and peripheral misinformation

This study used a laboratory-based paradigm to investigate social influences on participants’ susceptibility to misleading suggestions. Participants viewed a video clip of an action sequence with one or more peers, and then were required to discuss the event with the co-witness or with the group of co-witnesses. During the discussion a confederate, posing as a peer, presented misinformation about central and peripheral features of the co-witnessed event. Results indicated that participants were more susceptible to misleading suggestions during one-on-one discussions than during group discussions. In addition, participants were susceptible to misleading suggestions about central features of the witnessed event, although to a lesser extent than they were susceptible to misleading suggestions about peripheral features.     

Social suggestibility to central and peripheral misinformation

This study used a laboratory-based paradigm to investigate social influences on participants' susceptibility to misleading suggestions. Participants viewed a video clip of an action sequence with one or more peers, and then were required to discuss the event with the co-witness or with the group of co-witnesses. During the discussion a confederate, posing as a peer, presented misinformation about central and peripheral features of the co-witnessed event. Results indicated that participants were more susceptible to misleading suggestions during one-on-one discussions than during group discussions. In addition, participants were susceptible to misleading suggestions about central features of the witnessed event, although to a lesser extent than they were susceptible to misleading suggestions about peripheral features.     

The Word Superiority Effect in central and peripheral vision

The Word Superiority Effect (WSE) is a well-known phenomenon in reading research, where words are reported more accurately than single letters or non-words. We report two experiments that investigate the WSE in the central and peripheral visual field, as well as laterality differences in the perception of words and letters, using methods based on the Theory of Visual Attention. The results show a WSE in the central visual field, reflected in mean scores, perception thresholds, and processing speed, whereas the effect is eliminated or reversed in the periphery. This may be caused by crowding, which prevents lexical analysis of a word in the periphery. We conclude that perception of words and letters differs according to location in the visual field. Linking our results to previous studies of crowding effects in patients with reading impairments, we hypothesize that similar mechanisms may limit normal word peripheral processing.     

Apparent velocity of motion aftereffects in central and peripheral vision

Adapting to a drifting grating (temporal frequency 4 Hz, contrast 0.4) in the periphery gave rise to a motion aftereffect (MAE) when the grating was stopped. A standard unadapted foveal grating was matched to the apparent velocity of the MAE, and the matching velocity was approximately constant regardless of the visual field position and spatial frequency of the adapting grating. On the other hand, when the MAE was measured by nulling with real motion of the test grating, nulling velocity was found to increase with eccentricity. The nulling velocity was constant when scaled to compensate for changes in the spatial 'grain' of the visual field. Thus apparent velocity of MAE is constant across the visual field, but requires a greater velocity of real motion to cancel it in the periphery. This confirms that the mechanism underlying MAE is spatially-scaled with eccentricity, but temporally homogeneous. A further indication of temporal homogeneity is that when MAE is tracked, by matching or by nulling, the time course of temporal decay of the aftereffect is similar for central and for peripheral stimuli.