Coordination of symmetrical and asymmetrical human gait

Most human gait forms assume symmetrical, alternating patterns of interlimb coordination (e.g., crawling, walking, running). Human galloping is a notable exception. In contrast to extensive information on galloping in animals, little is known about this gait in humans. Therefore, kinematic and topographical analyses of running and galloping were undertaken to investigate the manner in which the lower limbs are uncoupled to produce this asymmetrical gait. Seven adult females were filmed while running and galloping at their preferred speed. Analysis of the gaits revealed differences in the following: (a) preferred speed, (b) coupling between upper- and lower-limb girdles, and (c) point of foot fall (end-point trajectories). In contrast to clear differences in interlimb coordination, intralimb coordination was remarkably similar across gaits, although when galloping was adopted, the rear leg did show more variable change than the front leg.     

Perception of the symmetrical patterning of human gait by infants

Two experiments tested 3- and 5-month-old infants' sensitivity to properties of point-light displays of human gait. In Experiment 1, infants were tested for discrimination of point-light displays of a walker and a runner, which, although they differed in many ways, were equivalent with regard to the phasing of limb movements. Results revealed that 3-month-old, but not 5-month-old, infants discriminated these displays. In Experiment 2, the symmetrical phase-patterning of the runner display was perturbed by advancing two of its limbs by 25% of the gait cycle. Both 3- and 5-month-old infants discriminated the walker display from this new phase-shifted runner display. These findings suggest that 3-month-old infants respond to the absolute and relative motions within a single limb, whereas 5-month-old infants respond primarily to the relations between limbs and, in particular, to the bilateral symmetry between the limbs.     

客体替代掩蔽:视觉后向掩蔽研究的新进展

传统的知觉实验通常采用视觉后向掩蔽在网膜水平上干扰对目标刺激的加工,主要有模式掩蔽和偏对比掩蔽两种形式.近年来客体替代掩蔽(简称OSM)的实验研究表明,围绕目标刺激呈现四个点也可导致目标刺激的可见性下降.OSM发生在客体表征水平上,它既是值得研究的掩蔽现象,也可以作为一种新的研究范式.本文介绍OSM的心理物理学和计算模型研究,并指出它对于认知科学的重要意义.     

Intentional compensation for selective loading affecting human gait phases

The locomotor strategies used by 12 subjects, instructed to hold their walking speed constant, were examined under various dynamic conditions in order to determine the means by which subjects can act upon their basic locomotor synergy. The dynamic conditions were modified either by adding a load or applying an impeding force. These modifications were designed to selectively affect either the stance phase or the swing phase. The results show that (a) subjects were able to rapidly calibrate their efforts to hold their walking speed constant, (b) in all conditions, the same walking speed was achieved with the same stride lengths and durations, and (c) at the within-cycle level, a change in duration synergically affected both phases and not just the perturbed one. The above results are discussed in terms of intentionally controlled parameters. Because cadence is closely linked to walking speed, it can be used as feedback; the control of walking speed in our experiments may thus be achieved simply by increasing the exerted force until the same cadence is produced.     

Metacontrast Masking and Attention

Metacontrast masking is generally considered an effect of preattentive processes operative in early vision. Because of the growing evidence of the role of attention in other phenomena previously considered low level and preattentive, its possible role in masking was explored in three experiments in which meaningful target stimuli known to capture attention (one's own name or a happy-face icon) were compared with control stimuli identical in spatial frequency and luminance. Not only were these salient stimuli significantly more resistant to masking than the control stimuli, but when one of the meaningful stimuli served as a mask, its strength was increased relative to a less meaningful variant, documenting the strong influence of attention on masking.     

Anthropometric characteristics and gait transition speed in human locomotion

The purpose of this study was to investigate the relationship between anthropometric parameters and the preferred transition speed (PTS) in human locomotion, in both genders. Previous studies exploring body measures as possible determinants of the PTS were biased toward longitudinal body dimensions, while the relationship between the PTS and transverse body dimensions has so far not been examined. Longitudinal and transverse anthropometric parameters were measured in 48 physical education students (21 males, 27 females), and an exercise test was performed for determination of the PTS. The relationship between the PTS and the anthropometric variables was determined using Pearson product-moment correlations and stepwise multiple regression analysis. Weak to moderate correlations between several body size and body shape variables and the PTS were found. In males, significant negative correlations (p<.05) between transverse body dimensions scaled to body height (calf girth, shoulder, bicristal and bitrochanteric diameters) and the PTS were found (r=-.51 to -.63). In females, calf girth and thigh girth scaled to height were significantly negatively correlated with the PTS (r=-.61 and -.42, respectively; p<.05). The results of the study suggest that gait transition speed in humans is related to both transverse and longitudinal body dimensions, and that sexual dimorphism in body size and shape should be taken into consideration for a proper interpretation of the PTS.     

视觉掩蔽研究现状及展望

视觉掩蔽是指某个物体因另一在空间或时间上与其相邻的物体的呈现而导致可见度降低的现象。目前,掩蔽的研究集中于那些涉及到特征、目标和场景表征,注意控制机制,以及现象知觉有关的加工等。该综述主要介绍了视觉掩蔽的概念和范式,研究的典型现象及参数,并介绍了相关的神经科学研究,概述并评论了4类重要的视觉掩蔽理论模型：知觉修正、双通道、边界轮廓系统以及目标替换。最后讨论了目前视觉掩蔽研究遇到的一些困难和挑战,包括刺激与任务的不统一带来的影响、神经科学方法的局限性以及模型模拟的复杂性,并从神经意识相关、功能性观点与模型发展三方面对视觉掩蔽未来的研究方向进行了展望。     

Masking by light and the sustained-transient dichotomy

Attention, Perception, & Psychophysics - An interpretation of masking by light in terms of the sustained-transient dichotomy is presented. It is proposed that presentation of a uniform flash...     

On Simultaneous Masking in the Visual Field

The concept of simultaneous masking in visual field is discussed, in the light of classical examples, of the various kinds of the phenomenon, of a modal completion, of the figure/ground phenomenon, of ambiguous and reversible figures, of mimicry and camouflage and eventually of the complexity of the stimulus. There is some reference to masking in auditory field. The “reality” of the masked configuration is discussed, drawing the conclusion that it is perceptually unreal. The fact that the masking phenomenon cannot take place without comparison between two perceptual acts – what we see at one moment and what we see a moment after LATER – and the fact that the masked configuration pops out with some surprise, lead to the conclusion that simultaneous masking in visual field is not a bare perceptual phenomenon, but a psychological process not unlike insight     

Auditory event perception: the source-perception loop for posture in human gait

There is a small but growing literature on the perception of natural acoustic events, but few attempts have been made to investigate complex sounds not systematically controlled within a laboratory setting. The present study investigates listeners' ability to make judgments about the posture (upright-stooped) of the walker who generated acoustic stimuli contrasted on each trial. We use a comprehensive three-stage approach to event perception, in which we develop a solid understanding of the source event and its sound properties, as well as the relationships between these two event stages. Developing this understanding helps both to identify the limitations of common statistical procedures and to develop effective new procedures for investigating not only the two information stages above, but also the decision strategies employed by listeners in making source judgments from sound. The result is a comprehensive, ultimately logical, but not necessarily expected picture of both the source-sound-perception loop and the utility of alternative research tools.     

Masking disrupts recovery of location information

In two experiments, we tested subjects’ ability to localize a letter in a character string with identification controlled by varying the delay of a mask, dimming the display, or deleting some of the dots used to define the letters on the cathode-ray screen. The first experiment involved two tasks. In the first task, subjects indicated whether or not a letter named verbally had been present in an eight-letter target string. In the second task, they localized a letter named verbally in the target string; the target string was presented by using display parameters shown in the first task to hold character identification between 70% and 75% correct. In the second experiment, we tallied errors in a partial-report bar-probe study after equating performance across the manipulations of display quality. Masking disrupted subjects’ ability to recover location information more than either a manipulation of stimulus luminance or a manipulation of its visual form.     

视觉掩蔽可基于知觉到的客体位置

利用flash—lag效应分离视觉掩蔽中客体的物理位置和知觉位置,以探讨掩蔽效应是否基于知觉到的客体位置。实验中掩蔽刺激做圆周运动,到某一位置时,目标刺激短时呈现,要求被试判断目标刺激（缺角菱形）的缺角方向。通过操作目标呈现时二者之间的相对位置,发现当二者物理位置不重合而知觉位置重合时掩蔽效应最大。该结果表明,视觉掩蔽可基于知觉到的客体位置。     

Quantitative analysis of human movement synergies: constructive pattern analysis for gait

To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.     

Masking of and by tactile pressure stimuli

Masking of and by tactile pressure stimuli was investigated in six Ss as a function of stimulus intensity (force) and stimulus onset asynchrony. Increase in the force of the masked stimulus and decrease in the force of the masking stimulus were inversely related to the magnitude of masking, as defined by either a relative or an absolute decrease in sensitivity. The introduction of stimulus onset asynchrony produced both forward and backward masking, the latter being of somewhat larger magnitude. Comparisons are made with results obtained in visual metacontrast masking.     

Masking by combination tones and bands

Masking of a pure tone by a cubic difference tone or band generated by two pure tones or by a pure tone and a narrow band of noise as a function of the level of the masker was measured for three subjects at three ratios of f₂/f₁, 1.125, 1,2, and 1.3. The three maskers used were f₁ alone, f₁ + f₂, and f₁ + NBN (60-Hz band of noise centered at f₂). At ratio 1.125, the amounts of masking produced by f₁ alone and f₁ + NBN were not significantly different for all subjects. For ratios = 1.125 and 1.2, f₁ + f₂ produced the least masking at least in two of the subjects. f₁ + NBN was the best masker at ratios 1.2 and 1.3. These results show that the masking data on cubic difference tone at very small ratios of f₂/f₁ are not reliable due to the masking effect contributed by f₁. For higher ratios, the combination band has to be used instead of combination tone because of the interaction between the signal and the cubic difference tone. Also the divergence of the effectiveness in masking by the three maskers gives an estimation of the levels of primaries at which the cubic difference tone is generated.     

Adaptation of neuromuscular synergies during intentional constraints of space-time relationships in human gait

Tight frequency-to-amplitude relationships are observed in spontaneous human steady gait. They can be modified, if required; that flexibility forms a fundamental basis of the intentional adaptive capabilities of locomotion. In the present experiments, the processes underlying that flexibility were investigated at both the level of joint kinematics and the level of neuromuscular synergies. Subjects (N = 4) walked at the same speed either with a preferred or a nonpreferred frequency-to-amplitude relationship (i.e., constrained, short steps at a high frequency [COS condition] or constrained, long steps at a low frequency [COL condition]); their swing and stance phases were separately analyzed. In the COS condition, increases in EMG activity were specifically required during the swing phase. In the COL condition, several muscles required increases in EMG activity during the stance phase, but decreases of the hamstring muscles were needed during the swing phase. Whereas, in preferred walking, modification of the frequency affects the EMG patterns globally (the gain increasing with the frequency in both the stance and swing phases), the present results show that changing the frequency in a constrained manner either affects the swing phase specifically or affects both phases, but in the opposite direction. That finding indicates that a separate control is needed in both the swing and the stance phases.     

Biomechanics of normal and pathological gait: implications for understanding human locomotor control

The biomechanical (kinetic) analysis of human gait reveals the integrated and detailed motor patterns that are essential in pinpointing the abnormal patterns in pathological gait. In a similar manner, these motor patterns (moments, powers, and EMGs) can be used to identify synergies and to validate theories of CNS control. Based on kinetic and EMG patterns for a wide range of normal subjects and cadences, evidence is presented that both supports and negates the central pattern generator theory of locomotion. Adaptive motor patterns that are evident in peripheral gait pathologies reinforce a strong peripheral rather than a central control. Finally, a three-component subtask theory of human gait is presented and is supported by reference to the motor patterns seen in a normal gait. The identified subtasks are (a) support (against collapse during stance); (b) dynamic balance of the upper body, also during stance; and (c) feedforward control of the foot trajectory to achieve safe ground clearance and a gentle heel contact.     

Perception of gait

Our ability of perceive the identity and naturalness of a human gait is examined in a series of four experiments involving computer-animated stick figures. The results indicate that the perceived naturalness of a walking or running gait can be influenced by the motion of any limb segment, but the perceived identity of these gaits is primarily determined by the movements of the lower leg (i.e., the tibia). The results also demonstrate that a perceptually salient walking gait can be transformed into running (or vice versa) by adding or subtracting a constant value to the angle of the lower leg over the entire step cycle. The size of this constant value is affected by the shape of the lower leg angle function and the motion of other limb segments.