Use of central and peripheral optical flow in stance and locomotion in young walkers

Young walkers (up to 5 years of age) were presented with optical flow in a moving room. Flow was global or was restricted to either the center or the periphery of the visible optic array. On standing trials the response rate was greatest when peripheral flow was available. The availability of central flow had a smaller effect on standing, and the younger children showed greater response rates to frontal flow than did the older ones. There was a strong negative correlation between age and response rate for all conditions. Flow also affected stability during locomotion. Response rate was again related to the location of the available flow. It is concluded that children show the same relative sensitivity for flow in the periphery of the dynamic structure of the optic array as has been observed in adults, but that this differentiation of different areas of optical structure is not yet fully developed when children learn to stand.     

The role of active locomotion in space perception

It has been shown that active control of locomotion increases accuracy and precision of nonvisual space perception, but psychological mechanisms of this enhancement are poorly understood. The present study explored a hypothesis that active control of locomotion enhances space perception by facilitating crossmodal interaction between visual and nonvisual spatial information. In an experiment, blindfolded participants walked along a linear path under one of the following two conditions: (1) They walked by themselves following a guide rope and (2) they were led by an experimenter. Subsequently, they indicated the walked distance by tossing a beanbag to the origin of locomotion. The former condition gave participants greater control of their locomotion and thus represented a more active walking condition. In addition, before each trial, half the participants viewed the room in which they performed the distance perception task. The other half remained blindfolded throughout the experiment. Results showed that although the room was devoid of any particular cues for walked distances, visual knowledge of the surroundings improved the precision of nonvisual distance perception. Importantly, however, the benefit of preview was observed only when participants walked more actively. This indicates that active control of locomotion allowed participants to better utilize their visual memory of the environment for perceiving nonvisually encoded distance, suggesting that active control of locomotion served as a catalyst for integrating visual and nonvisual information to derive spatial representations of higher quality.     

The kinematics of locomotion toward a goal

A mathematical model is developed that treats rats in runways as uniformly accelerated bodies. The purpose of the model is to permit conversion of the continuously varying measures of runway speeds at different points in the alley into three invariant parameters of performance: start latency, acceleration, and brakepoint. This simple model fits most of the data examined, and changes in the parameters throw new light on phenomena such as the partial reinforcement acquisition effect. In particular, it is shown that partially reinforced rats accelerate faster but cease accelerating earlier in the runway than do continuously reinforced rats. This explains the qualitative differences often found between start and goal speed measures. The analysis takes as its unit patterns of terminal behavior rather than the rate of the responses that constitutes them, and thus may permit coherent treatment of instrumental and operant behavior.     

The impact of object carriage on independent locomotion

The current study examined whether carrying objects in one's hands influenced different parameters associated with independent locomotion. Specifically, 14- and 24-month-olds walked in a straight path under four conditions of object carriage – no object (control), one object carried in one hand (one object-one hand), two objects carried in each of the hands (two objects-two hands), and one object carried in both hands simultaneously (one object-two hands). Although carrying objects failed to influence a variety of kinematic parameters of gait, it did affect children's arm postures, with children adopting less mature arm positions when carrying objects. Finally, arm position was related to walking skill, but only for older children when they were not carrying objects. These findings indicate that although a relation does exist between arm positions and gait parameters, this relation is easily disrupted by carrying loads, even small ones.     

The relationship between allometry and preferred transition speed in human locomotion

The purpose of this study was to explore the relationships between preferred transition speed (PTS) and anthropometric characteristics, body composition and different human body proportions in males. In a sample of 59 male students, we collected anthropometric and body composition data and determined individual PTS using increment protocol. The relationships between PTS and other variables were determined using Pearson correlation, stepwise linear and hierarchical regression. Body ratios were formed as quotient of two variables whereby at least one significantly correlated to PTS. Circular and transversal (except bitrochanteric diameter) body dimensions did not correlate with PTS. Moderate correlations were found between longitudinal leg dimensions (foot, leg and thigh length) and PTS, while the highest correlation was found for lower leg length (r = .488, p < .01). Two parameters related to body composition showed weak correlation with PTS: body fat mass (r = −.250, p < .05) and amount of lean leg mass scaled to body weight (r = .309, p < .05). Segmental body proportions correlated more significantly with PTS, where thigh/lower leg length ratio showed the highest correlation (r = .521, p < .01). Prediction model with individual variables (lower leg and foot length) have explained just 31% of PTS variability, while model with body proportions showed almost 20% better prediction (R² = .504). These results suggests that longitudinal leg dimensions have moderate influence on PTS and that segmental body proportions significantly more explain PTS than single anthropometric variables.     

The learning of goal-directed locomotion: A perception-action perspective

This study was designed to better understand the process underlying the learning of goal-directed locomotion. Subjects walked on a treadmill in a virtual reality setting and were asked to cross pairs of oscillating doors. The subjects' behaviour was examined at the beginning of the learning process (pretest), after 350 trials (intermediate test), and after 700 trials (posttest). The data were analysed at three different levels, each representing a specific aspect of the global response: performance outcome, displacement kinematics, and current arrival condition. While some aspects of performance outcome suggested the presence of a ceiling effect in the intermediate test, both displacement kinematics and current arrival condition clearly highlighted continuous transformations of the control mechanism involved. The learning process is best described as (1) the establishing of a relationship between specific information and a movement parameter and (2) the optimization of this relationship. The optimization process is characterized by the further exploration of the available behavioural repertoire and by the refinement of the dialogue between information and movement.     

Movement parallax during locomotion

A hypothesis concerning the nature of movement parallax during locomotion is presented. According to the hypothesis, movement parallax constitutes a basic perceptual-motor mechanism able to produce veridical information as to spatial relations in three-dimensional space. Two experiments are reported verifying the hypothesis in that information due to movement parallax unequivocally dominated both the effects of proximal relative size and spatial anisotropy.     

The role of visual and nonvisual information in the control of locomotion

During locomotion, retinal flow, gaze angle, and vestibular information can contribute to one's perception of self-motion. Their respective roles were investigated during active steering: Retinal flow and gaze angle were biased by altering the visual information during computer-simulated locomotion, and vestibular information was controlled through use of a motorized chair that rotated the participant around his or her vertical axis. Chair rotation was made appropriate for the steering response of the participant or made inappropriate by rotating a proportion of the veridical amount. Large steering errors resulted from selective manipulation of retinal flow and gaze angle, and the pattern of errors provided strong evidence for an additive model of combination. Vestibular information had little or no effect on steering performance, suggesting that vestibular signals are not integrated with visual information for the control of steering at these speeds.     

Inconsistent locomotion inhibits vection

We measured the strength of illusory self-motion perception (vection) with and without locomotion on a treadmill. The results revealed that vection was inhibited by inconsistent locomotion, but facilitated by consistent locomotion.     

Visual control of locomotion

Abstract.— How is locomotion controlled? What information is necessary and how is it used? It is first of all argued that the classical twofold division of information into ex-teroceptive and proprioceptive is inadequate and confusing, that three fundamental types of information need to be distinguished and that the information is used in a continual process of formulating locomotor programs, monitoring their execution and adjusting them. The paper goes on to show (1) how steering could be controlled on the basis of the “locomotor flow line” in the optic array, which specifies the potential future course, whether curved or straight, and (2) how stopping for an obstacle could be controlled simply on the basis of the information in the optic array about the time-to-collision and its rate of change. The problems inherent in pedestrian locomotion of controlling footing and balance are discussed and an investigation of visual locomotor programming in the long jump reported.     

Incidental sounds of locomotion in animal cognition

The highly synchronized formations that characterize schooling in fish and the flight of certain bird groups have frequently been explained as reducing energy expenditure. I present an alternative, or complimentary, hypothesis that synchronization of group movements may improve hearing perception. Although incidental sounds produced as a by-product of locomotion (ISOL) will be an almost constant presence to most animals, the impact on perception and cognition has been little discussed. A consequence of ISOL may be masking of critical sound signals in the surroundings. Birds in flight may generate significant noise; some produce wing beats that are readily heard on the ground at some distance from the source. Synchronization of group movements might reduce auditory masking through periods of relative silence and facilitate auditory grouping processes. Respiratory locomotor coupling and intermittent flight may be other means of reducing masking and improving hearing perception. A distinct border between ISOL and communicative signals is difficult to delineate. ISOL seems to be used by schooling fish as an aid to staying in formation and avoiding collisions. Bird and bat flocks may use ISOL in an analogous way. ISOL and interaction with animal perception, cognition, and synchronized behavior provide an interesting area for future study.     

The force-driven harmonic oscillator model for energy-efficient locomotion in individuals with transtibial amputation

The force-driven harmonic oscillator (FDHO) model states that the driving force is minimum at the resonant period of an oscillator. By manipulating prosthetic mass, this study explored the compromise of resonant periods between the two legs in persons with unilateral traumatic transtibial amputation (TTA) at self-selected walking velocity (SSWV), with an aim to better understand the energy minimization mechanisms of walking. It was hypothesized that (1) SSWV was the most energy-efficient walking velocity (MEWV), (2) the stride period at SSWV (Ts) is a compromise between the resonant periods of the normal leg (Tn) and the prosthetic leg (Tp) when they are dissimilar. Eight subjects completed multiple-speed treadmill walking tests (at 53, 67, 80, 93, and 107 m/min) according to three mass conditions (60%, 80%, and 100% of the normal leg below-knee mass) in a random order. Oxygen consumption and stride period were measured, and SSWV was empirically determined. The MEWV, the speed with minimum energy expenditure per distance traveled, was derived from quadratic regression, and its stride period (Tm) was estimated. A theoretical compromise period (Tv) between Tn and Tp was predicted by a virtual single pendulum system based on Huygens' Law. Across different mass conditions, comparisons were made among: Ts, Tm, Tv, Tn, and Tp. Results showed that: (1) Ts was significantly different from Tm; (2) Ts was greater than both Tn and Tp; (3) no significant difference was found between Tm and Tn. Implications for amputee rehabilitation in terms of thigh muscle training and prosthesis development were discussed.     

The role of locomotion in the acquisition and transfer of spatial knowledge in children

The role of locomotion in the acquisition and transfer of spatial knowledge was investigated in 144 five-, seven- and eleven-year-old children. Two experiments were conducted in the Kiel locomotor maze. In the first experiment, one group of children explored the spatial layout by walking through the maze, while another learned the maze by surveying the layout. In the second experiment, children were exposed to one of two orientation tests in the maze, one of which could be solved using "landmark orientation", the other only using a "relational place orientation". Children sitting by the side of the experimental chamber surveying the maze needed fewer trials to learn the spatial layout than children exploring the environment in the locomotion condition, but in the orientation test demanding the "relational place orientation" children who had explored the maze in the locomotion condition outperformed the children in the non-locomotion condition. Results are discussed in the context of cognitive mapping models.     

Learning the pedalo locomotion task

The authors examined the learning function of a multiple biomechanical degrees of freedom coordination task. Four adult participants practiced the pedalo locomotion task for 350 trials over 7 days. On the basis of the Cauchy theorem, the authors applied a movement pattern difference score that provides a measure of convergence to a fixed point as the criterion for quantifying learning. The findings showed a significant reduction of the movement pattern difference score over practice. Neither an exponential (0.11) nor a power law (0.10) function accommodated a large percentage of the variance of the pattern difference measure on individual learning functions, but the respective fits were higher, although not different, for movement time (.57, .55). Principal components analysis showed a decrease of components over practice; the analysis also showed that 3-5 components were required to accommodate 90% of the variance of the whole-body motion at the end of the final practice session. Those findings on the learning functions for movement and outcome scores are discussed in relation to the redundancy of the biomechanical system in moving to a dynamical stable fixed point in this task.     

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.     

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.     

The role of gaze and road edge information during high-speed locomotion

Robust control of skilled actions requires the flexible combination of multiple sources of information. Here we examined the role of gaze during high-speed locomotor steering and in particular the role of feedback from the visible road edges. Participants were required to maintain one of three lateral positions on the road when one or both edges were degraded (either by fading or removing them). Steering became increasingly impaired as road edge information was degraded, with gaze being predominantly directed toward the required road position. When either of the road edges were removed, we observed systematic shifts in steering and gaze direction dependent upon both the required road position and the visible edge. A second experiment required fixation on the road center or beyond the road edges. The results showed that the direction of gaze led to predictable steering biases, which increased as road edge information became degraded. A new steering model demonstrates that the direction of gaze and both road edges influence steering in a manner consistent with the flexible weighted combination of near road feedback information and prospective gaze information.     

Conditioning the cardiorespiratory dynamics of locomotion in dogs

In 17 dogs blood pressure in the carotid artery, heart rate, pneumogram and actogram of the hind leg were recorded during rest and during locomotion on a treadmill. The increases in cardiorespiratory dynamics which occurred during locomotion were then conditioned. The conditional stimulus was represented by the noise and vibration of the treadmill. It was determined that conditional changes in cardiorespiratory dynamics can be formed quickly on the basis of locomotion. Qualitatively the changes were the same as the unconditional changes, and their magnitude was 60 to 70 per cent that of the unconditional changes. Conditional increase in cardiorespiratory dynamics was most intensive in the first 30 seconds from the onset of the conditional stimulus. In acute extinction of these conditional changes, movements of the extremities were inhibited first, followed by inhibition of increased blood pressure, then inhibition of increased heart rate, and last, inhibition of increased respiratory rate. In another series of experiments on five dogs cardiorespiratory responses were conditioned to a sudden change from moderate locomotion (50 m per min) to rapid locomotion (200 m per min). Increased cardiorespiratory dynamics could be conditioned easily. Increased circulation of blood and increased respiratory rate on exposure to conditional stimuli signalling muscular exertion can be considered an important preparation of the organism for actual muscular activity. This preparation also takes place in natural life conditions.