Effects of toe length,foot arch length and toe joint axis on walking biomechanics

Toe joint articulation has been shown to affect gait mechanics, as evidenced by walking simulations, biped robots, and foot prostheses. However, it is not known how parameters such as toe length, foot arch length (i.e., heel-to-toe-joint length) or toe joint axis angle affect human walking. We utilized a previously developed adjustable ankle-toe prosthesis to systematically examine these three foot parameters. We tested ten able-bodied persons walking on a force instrumented-treadmill while wearing a pair of adjustable prostheses attached bilaterally below simulator boots (which fixated their biological ankles). We collected motion and ground reaction force data to compute lower-limb kinematics and kinetics as well as COM power and work. We observed that increasing the foot arch length by 60 mm (35%) increased COM Push-off work by ~5 J, due to increased energy storage and return by the ankle spring. Increasing the toe length by 40 mm (80%) and changing the toe joint axis by ±9° from a neutral angle resulted in negligible effects on COM mechanics and lower limb kinetics. This study provides further insights regarding toe joint function; knowledge which may benefit the design/integration of toe joints into prostheses, exoskeletons and legged robots.     

液晶显示器上字符辨认效果与观察角度及字符大小的关系

本研究从工程心理学角度,探讨了有源矩阵液晶显示器上字符辨认效果与观察角度及字符大小的关系。实验结果表明：(1)液晶显示的字符辨认效果因观察角度不同而存在显著差异,无论是在水平方向上还是下视方向上,字符辨认错误率均随着观察角度的增大而先慢后快地上升;但相比之下,水平方向上观察角度变化的容许范围大于下视方向上的容许范围;(2)液晶显示器上字符辨认效果也受字符大小的影响,并且字符大小与观察角度之间存在着显著的交互作用;当观察角度较大时,可通过加大字符尺寸来提高视觉辨认效果。     

Locomotor Patterns of the Leading and the Trailing Limbs as Solid and Fragile Obstacles Are Stepped Over: Some Insights Into the Role of Vision During Locomotion

The issues explored in this article are the role of exproprioceptive input and the nature of exteroceptive input provided by the visual system in the control of limb elevation as obstacles are stepped over during locomotion. In the first experiment, the differences in limb trajectory of movements over solid and fragile obstacles of similar dimensions were examined. Subjects increased their toe clearance, vertical position of the hip, and the hip vertical velocity when going over a fragile obstacle with the leading limb. This suggests that in addition to visually observable properties of obstacles such as height or width, other properties, such as rigidity or fragility, which may be classified as visually inferred, also influence the limb trajectory. Part of the first and the second experiment was focused on understanding differences in leading limb and trailing limb trajectory over obstacles. The toe clearance of the trailing limb was lower for smaller obstacles. There was no consistent correlation between the toe clearance values of the leading and trailing limbs. The variability in toe clearance was higher for the trailing limb, which is attributable to lack of visual exproprioceptive input about trailing limb movements and to the shorter time available following toe-off to fine-tune the trailing limb trajectory. Because the body center of mass is moving toward the supporting foot when the trailing limb goes over obstacles and the trailing limb foot is moving up, the chances of a trip are minimized and recovery from an unexpected trip are more likely. These results highlight the role of exproprioceptive input provided by the visual system and possible cognitive influences on the limb trajectory as one travels over uneven terrains.     

Perceived direction of rotation of simulated three-dimensional patterns

Direction of rotation judgments were obtained from 72 subjects for computer-generated dot patterns simulating points randomly distributed in a sphere rotating about a vertical axis. The displays were produced either with normal polar projections or with perspective effects limited to the horizontal or to the vertical dimension of the projection. The simulated viewing distance used in the projections and the visual angle subtended by the projected displays were also varied. Accuracy of direction judgments was about the same with perspective effects limited to the vertical dimension as with normal polar projections but did not exceed chance expectations with perspective effects limited to the horizontal dimension. Accuracy was lower at the greater simulated viewing distance and at the greater visual angle.     

Selection of movement patterns during functional tasks in humans

These experiments examine the role of vision and step height in the selection of a simple binary choice of movement pattern by human subjects. The subjects selected a heel strike movement pattern (HS) (as used during level surface locomotion) or a toe strike movement pattern (TS) (as used during stair descent). The functional task involved descending a step of adjustable height followed by level surface walking under vision and nonvision conditions. Triceps surae and tibialis anterior electromyographic (EMG) activity, ankle angle position, and vertical force were examined. As step height was increased, there was an indistinct threshold at which subjects switched from landing with a HS movement pattern to a TS movement pattern. The tibialis anterior and triceps surae precontact EMG burst and subsequent ankle movement for HS and TS trials appear to be part of preprogrammed movement patterns, which are presumably of central origin. The particular mixture of voluntary, stereotypic, and reflex actions for any specified movement is based on the intent or functional outcome desired. The switching to the TS movement pattern as step height increased presumably results in the most efficient and stable movement.     

Selection of Movement Patterns During Functional Tasks in Humans

These experiments examine the role of vision and step height in the selection of a simple binary choice of movement pattern by human subjects. The subjects selected a heel strike movement pattern (HS) (as used during level surface locomotion) or a toe strike movement pattern (TS) (as used during stair descent). The functional task involved descending a step of adjustable height followed by level surface walking under vision and nonvision conditions. Triceps surae and tibialis anterior electromyographic (EMG) activity, ankle angle position, and vertical force were examined. As step height was increased, there was an indistinct threshold at which subjects switched from landing with a HS movement pattern to a TS movement pattern. The tibialis anterior and triceps surae precontact EMG bursts and subsequent ankle movement for HS and TS trials appear to be part of preprogrammed movement patterns, which are presumably of central origin. The particular mixture of voluntary, stereotypic, and reflex actions for any specified movement is based on the intent or functional outcome desired. The switching to the TS movement pattern as step height increased presumably results in the most efficient and stable movement.     

Subtasks affecting step-length asymmetry in post-stroke hemiparetic walking

This study was performed to investigate whether components from trunk progression (TP) and step length were related to step length asymmetry in walking in patients with hemiparesis. Gait analysis was performed for participants with hemiparesis and healthy controls. The distance between the pelvis and foot in the anterior-posterior axis was calculated at initial-contact. Step length was partitioned into anterior foot placement (AFP) and posterior foot placement (PFP). TP was partitioned into anterior trunk progression (ATP) and posterior trunk progression (PTP). The TP pattern and step length pattern were defined to represent intra-TP and intra-step spatial balance, respectively. Of 29 participants with hemiparesis, nine participants showed longer paretic step length, eight participants showed symmetric step length, and 12 participants showed shorter paretic step length. For the hemiparesis group, linear regression analysis showed that ATP asymmetry, AFP asymmetry, and TP patterns had significant predictability regarding step length asymmetry. Prolonged paretic ATP and shortened paretic AFP was the predominant pattern in the hemiparesis group, even in participants with symmetric step length. However, some participants showed same direction of ATP and AFP asymmetry. These findings indicate the following: (1) ATP asymmetries should be observed to determine individual characteristics of step length asymmetry, and (2) TP patterns can provide complementary information for non-paretic limb compensation.     

Advancing age progressively affects obstacle avoidance skills in the elderly

The ability to adequately avoid obstacles while walking is an important skill that allows safe locomotion over uneven terrain. The high proportion of falls in the elderly that is associated to tripping over obstacles potentially illustrates an age-related deterioration of this locomotor skill. Some studies have compared young and old adults, but very little is known about the changes occurring within different age groups of elderly. In the present study, obstacle avoidance performance was studied in 25 young (20-37 years) and 99 older adults (65-88 years). The participants walked on a treadmill at a speed of 3 km/h. An obstacle was dropped 30 times in front of the left foot at various phases in the step cycle. Success rates (successful avoidance) were calculated and related to the time available between obstacle appearance and the estimated instant of foot contact with the obstacle (available response times or ARTs ranging from 200 to more than 350 ms). In addition, latencies of avoidance reactions, the choice of avoidance strategies (long or short step strategy, LSS or SSS), and three spatial parameters related to obstacle avoidance (toe distance, foot clearance, and heel distance) were determined for each participant. Compared to the young, the older adults had lower success rates, especially at short ARTs. Furthermore, they had longer reaction times, more LSS reactions, smaller toe and heel distances, and larger foot clearances. Within the group of elderly, only the 65-69 year olds were not different from young adults with respect to success rate, despite marked changes in the other parameters measured. In particular, even this younger group of elderly showed a dramatic reduction in the amount of SSS trials compared to young adults. Overall, age was a significant predictor of success rates, reaction times, and toe distances. These parameters deteriorated with advancing age. Finally, avoidance success rates at short ARTs were considerably worse in elderly participants who sustained recurrent falls in the six-month period prior to the assessment compared to those who sustained no or only one fall. An exercise program has been shown to improve avoidance success rates, especially at short ARTs, but the training effects on the determinants of success still need to be assessed.     

Anisotropic perception of visual angle: implications for the horizontal-vertical illusion, overconstancy of size, and the moon illusion.

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20 degrees to 80 degrees were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5 degrees-30 degrees were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3 degrees-80 degrees were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, theta' = a + b theta + c theta 2 (where theta is the visual angle; theta', the obtained angle; a, b, and c, constants). (2) The linear coefficient b is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficient c is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.     

Visual distortion of body size modulates pain perception

Pain is a complex subjective experience that is shaped by numerous contextual factors. For example, simply viewing the body reduces the reported intensity of acute physical pain. In this study, we investigated whether this visually induced analgesia is modulated by the visual size of the stimulated body part. We measured contact heat-pain thresholds while participants viewed either their own hand or a neutral object in three size conditions: reduced, actual size, or enlarged. Vision of the body was analgesic, increasing heat-pain thresholds by an average of 3.2 °C. We further found that visual enlargement of the viewed hand enhanced analgesia, whereas visual reduction of the hand decreased analgesia. These results demonstrate that pain perception depends on multisensory representations of the body and that visual distortions of body size modulate sensory components of pain.     

工作记忆负荷、形状干扰对聋人与听力正常人注意捕获影响的眼动研究

通过记录和分析被试的行为和眼动指标,本研究试图探讨不同工作记忆负荷下,形状干扰对聋人与听力正常人不同视野位置上刺激信息捕获注意的异同。研究结果表明：（1）形状干扰刺激虽然没有影响被试视觉加工的认知绩效,但被试的眼动模式会由于工作记忆负荷的改变而改变,高工作记忆负荷时,有形状干扰的注视次数高于无形状干扰。（2）工作记忆负荷、视野位置影响被试视觉加工任务的完成,被试在不同视野位置的加工过程表现出不一致的眼动模式。（3）聋人视觉加工在高工作记忆负荷时存在一定的劣势,但其对不同视野位置的信息加工及形状干扰所产生的注意捕获效应与听力正常人一致。     

Repeated exposure to tripping like perturbations elicits more precise control and lower toe clearance of the swinging foot during steady walking

Controlling minimum toe clearance (MTC) is considered an important factor in preventing tripping. In the current study, we investigated modifications of neuro-muscular control underlying toe clearance during steady locomotion induced by repeated exposure to tripping-like perturbations of the right swing foot. Fourteen healthy young adults (mean age 26.4 ± 3.1 years) participated in the study. The experimental protocol consisted of three identical trials, each involving three phases: steady walking (baseline), perturbation, and steady walking (post-perturbation). During the perturbation, participants experienced 30 tripping-like perturbations at unexpected timing delivered by a custom-made mechatronic perturbation device. The temporal parameters (cadence and stance phase_%), mean, and standard deviation of MTC were computed across approximately 90 strides collected during both baseline and post-perturbation phases, for all trials. The effects of trial (three levels), phase (two levels: baseline and post-perturbation) and foot (two levels: right and left) on the outcome variables were analyzed using a three-way repeated measures analysis of variance. The results revealed that exposure to repeated trip-like perturbations modified MTC toward more precise control and lower toe clearance of the swinging foot, which appeared to reflect both the expectation of potential forthcoming perturbations and a quicker compensatory response in cases of a lack of balance. Moreover, locomotion control enabled subjects to maintain symmetric rhythmic features during post-perturbation steady walking. Finally, the effects of exposure to perturbation quickly disappeared among consecutive trials.     

Anisotropic perception of visual angle: Implications for the horizontal-vertical illusion,overconstancy of size,and the moon illusion

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20° to 80° were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5°–30° were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3°-80° were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, θ′=a+bθ+cθ² (where θ is the visual angle; θ′, the obtained angle;a, b, andc, constants). (2) The linear coefficientb is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficientc is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.     

Visual control of step length during running over irregular terrain

Running over uneven ground requires visually regulating step length to secure proper footing. To examine how this is achieved, we studied subjects running on a treadmill on a series of irregularly spaced targets. The movements of their lower limbs and coccyx relative to the targets were monitored opto-electronically by a Selspot system. The results indicated that step length was adjusted to strike the targets primarily by varying the vertical component of impulse applied to the ground during the stance phase. In contrast, horizontal impulse was not varied significantly, and changing the reach forward of the foot on landing contributed little to variation in step length. Changing the vertical impulse simply altered the step time proportionately. Thus the data are consistent with a time-based model in which vertical impulse is modulated by the optic variable delta tau (Lee, 1976) specifying the time gap that has to be bridged by the runner between two targets.     

The effect of visual magnification and reduction on perceived hand size

The aim of the present study was to clarify the mechanisms underlying body understanding by examining the impact of visual experience (magnification and reduction) on perception of hand size and neutral external objects (squares). Independent groups of participants were asked to look through a 2× magnification lens, a ½-× reduction lens, or a control UV filter and to make visual size judgments about square stimuli and their hands. In Experiment 1, participants used a measuring device with unmarked wooden slats orientated in horizontal and radial/vertical space for their visual judgments. In Experiment 2, participants used an upright frontal slat for visual length judgments of their hands to eliminate any potential foreshortening in viewing the measurement apparatus. The results from the two experiments demonstrate that participants significantly underestimated both the square stimuli and their hands when they viewed them under a reduction lens. While overestimation and underestimation of squares was found for females in Experiment 2, males generally underestimated the squares. However, overestimation was not seen when the participants viewed their hands under a magnification lens. Implications of these findings are discussed.     

Thumb's rule tested: visual angle of thumb's width is about 2 deg.

Measures of the size of various hand parts and their viewing distance when held at arm's length were made on one hundred and eighteen undergraduate students. A simple rule of thumb can be confirmed: Visual angle of the width of the thumb held at arm's length is about 2 deg. The thumbnail subtends about 1.5 deg and the index fingernail about 1 deg in width, when both are held at arm's length. These figures are good approximations for males and females, although a significant, direct, linear relationship exists between hand-part size and the visual angle of the part at arm's length.     

物体相似性对空间表征的影响：来自眼动的证据

以三维场景图片为实验材料,采用眼动追踪技术,通过两个实验考察了对称场景中物体相似性对空间表征的影响。结果表明：（1）无相似物体条件下,场景本身的内在结构对空间表征有重要影响,对称轴方向可以作为空间表征参照方向;（2）存在部分相似物体条件下,物体的相似性会影响空间表征参照方向的选择,并且相似物体方向也是空间表征的参照方向之一。     

The use of auditory feedback and edible reinforcement to decrease toe walking among children with autism

We replicated and extended previous research on the use of auditory feedback to decrease toe walking exhibited by 3 children with autism. After pretreatment screening analyses suggested that toe walking occurred independent of social consequences, we attached squeakers to the heels of each participants' shoes. The squeakers provided auditory feedback when participants walked appropriately (i.e., with a heel-to-toe gait). For all participants, the auditory feedback itself produced increases in appropriate walking. For 1 participant, this feedback was sufficient to reduce toe walking to clinically acceptable levels; however, for 2 other participants, delivery of edible items paired with the auditory feedback was necessary. Intervention effects maintained when the schedule for edible delivery was thinned for all participants. In addition, for 2 participants, effects maintained when the intervention was implemented in a different setting and with a different person with no edibles or a thin schedule of edibles.     

Visual and haptic matching of perceived orientations of lines

In this study we investigated the perception and production of line orientations in a vertical plane. Previous studies have shown that systematic errors are made when participants have to match oblique orientations visually and haptically. Differences in the setup for visual and haptic matching did not allow for a quantitative comparison of the errors. To investigate whether matching errors are the same for different modalities, we asked participants to match a visually presented orientation visually, haptically with visual feedback, and haptically without visual feedback. The matching errors were the same in all three matching conditions. Horizontal and vertical orientations were matched correctly, but systematic errors were made for the oblique orientations. The errors depended on the viewing position from which the stimuli were seen, and on the distance of the stimulus from the observer.     

How long is your arm? Using multisensory illusions to modify body image from the third person perspective

Updating body representations from the 3rd person perspectives (3PP) seems to require viewing the real body, unlike when viewing from a 1st person perspective. Here, 3PP updating was investigated through induction of a physically impossible multisensory illusion in which participants viewed real-time 3PP video of themselves having their arm pulled until it stretched to twice its normal length. The illusion elicited the subjective experience that the participant's own arm had been stretched and caused an overestimation of reaching distance, although actual reaches were unaffected. Multisensory illusions from the 3PP can alter body image when applied to real bodies.