Center-of-pressure regularity as a marker for attentional investment in postural control: A comparison between sitting and standing postures

Postural control is a highly automatized basic activity that requires limited attentional investments. These investments have been shown to increase from balancing experts to controls, and from controls to persons with impaired postural control. Such between-subject comparisons led to a proposed direct relation between the regularity of center-of-pressure (COP) fluctuations and the amount of attention invested in posture. This study aims to expand this relation to a within-subject comparison of conditions that differ in balance demands. Specifically, more regular COP fluctuations were expected for standing than sitting, as stimulus-response reaction-time studies showed that the required attentional demands are lower for sitting than standing. COP registrations were made for fifteen healthy young adults in seated and standing postures. COP regularity was quantified with sample entropy. As expected, COP fluctuations were found to be more regular for standing than sitting, as evidenced by significantly lower sample entropy values. These findings expand the relation between COP regularity and the amount of attention invested in posture to postural tasks that vary in balance demands. An assessment of COP regularity may thus not only be instrumental in the examination of attentional investment in posture in between-subject designs, but also for different postures in within-subjects designs.     

Coupling of postural and manual tasks in expert performers

The purpose of this study was to investigate the integration of bimanual rhythmic movements and posture in expert marching percussionists. Participants (N = 11) performed three rhythmic manual tasks [1:1, 2:3, and 2:3-F (2:3 rhythm played faster at a self-selected tempo)] in one of three postures: sitting, standing on one foot, and standing on two feet. Discrete relative phase, postural time-to-contact, and coherence analysis were used to analyze the performance of the manual task, postural control, and the integration between postural and manual performance. Across all three rhythms, discrete relative phase mean and variability results showed no effects of posture on rhythmic performance. The complexity of the manual task (1:1 vs. 2:3) had no effect on postural time-to-contact. However, increasing the tempo of the manual task (2:3 vs. 2:3-F) did result in a decreased postural time-to-contact in the two-footed posture. Coherence analysis revealed that the coupling between the postural and manual task significantly decreased as a function of postural difficulty (going from a two-footed to a one-footed posture) and rhythmic complexity (1:1 vs. 2:3). Taken together, these results demonstrate that expert marching percussionists systematically decouple postural and manual fluctuations in order to preserve the performance of the rhythmic movement task.     

身体姿势的心理效应：基于具身视角

具身视角下，姿势可以对心理产生影响。梳理了广受关注的“直立”和“蜷曲”、“扩张”和“收缩”、“水平”和“垂直”等姿势的效应研究成果，并对神经肌肉反馈理论、自我知觉理论、情境认知理论等姿势效应的内在机制进行总结和评价。指出在实验范式、姿势控制、效应稳定性以及深层机制探析等方面存在的局限和未来方向，认为姿势效应的神经机制、时程变化、个体差异及姿势的心理调节功能等将会成为研究热点。     

Ipsilesional arm reaching movements are not affected by the postural configuration adopted by individuals with stroke

Individuals with stroke present several impairments in the ipsilesional arm reaching movements that can limit the execution of daily living activities. These impairments depend on the side of the brain lesion. The present study aimed to compare the arm reaching movements performed in sitting and standing positions and to examine whether the effects of the adopted posture configuration depend on the side of the brain lesion. Twenty right-handed individuals with stroke (half with right hemiparesis and a half with left hemiparesis) and twenty healthy adults (half used the left arm) reached toward a target displayed on a monitor screen placed in one of three heights (i.e., upper, central, or lower targets). Participants performed the reaches in sitting and standing positions under conditions where the target location was either well-known in advance (certainty condition) or unknown until the movement onset (uncertainty condition). The values of movement onset time, movement time, and constant error were compared across conditions (posture configuration and uncertainty) and groups for each target height. Individuals with stroke were slower and spent more time to start to move than healthy participants, mainly when they reached the superior target in the upright position and under the uncertainty condition. Individuals who have suffered a right stroke were more affected by the task conditions and those who suffered a left stroke showed less accurate reaches. Overall, these results were observed regardless of the adopted posture. The current findings suggested that ipsilesional arm reaching movements are not affected by the postural configuration adopted by individuals with stroke. The central nervous system modulates the reaching movements according to the target position, adopted posture, and the uncertainty in the final target position to be reached.     

Grasp posture planning during multi-segment object manipulation tasks — Interaction between cognitive and biomechanical factors

The present study examined adaptations in the planning of initial grasp postures during a multi-segment object manipulation task. Participants performed a grasping and placing task that consisted of one, two, or three movement segments. The position of the targets was manipulated such that the degree of object rotation between the home and temporally proximal positions, and between the temporally proximal and distal target positions, varied. Participants selected initial grasp postures based on the specific requirements of the temporally proximal and temporally distal action segments, and adjustments in initial grasp posture depended on the temporal order of target location. In addition, during the initial stages of the experimental session initial grasp postures were influenced to a larger extent by the demands of the temporally proximal segment. However, over time, participants overcame these cognitive limitations and adjusted their initial grasp postures more strongly to the requirements of the temporally distal segment. Taken together, these results indicate that grasp posture planning is influenced by cognitive and biomechanical factors, and that participants learn to anticipate the task demands of temporally distal task demands, which we hypothesize, reduce the burden on the central nervous system.     

A test of the ability to identify emotion in human standing and sitting postures: the diagnostic analysis of nonverbal accuracy-2 posture test (DANVA2-POS)

The purpose of the present study was to introduce the Diagnostic Analysis of Nonverbal Accuracy for Postures (DANVA2-POS), a test that measures an individual's ability to identify emotion in human standing and sitting postures. The authors describe the construction and selection of the test items. Types of standing and sitting postures were generated from a set of dimensions gleaned from a review of relevant theoretical and empirical literature. Two men and 2 women portraying standing and sitting postures were photographed. An empirical norming procedure was used to select 32 high- and low-intensity standing and sitting postures representing happiness, sadness, anger, and fear. Three hypotheses guided the collection of construct validity evidence. Consistent with the hypotheses, data from 243 participants showed that DANVA2-POS scores increased in accuracy with age, were internally consistent and reliable over time, and were related to self-reported loneliness, fear of negative evaluation, and locus of control. The authors report construct validity evidence from 6 additional studies. Future applications of the DANVA2-POS test are described.     

The Perception of Self-Motion Induced by Peripheral Visual Information in Sitting and Supine Postures

The effects of speed and direction of a moving peripheral stimulus on the perception of self-motion were studied in sitting and supine postures. Observers sat or lay on their backs with one monitor on each side of their head. On the monitor screens, random dot patterns moved vertically or horizontally under three speed conditions. The latency of the onset of the induced self-motion was shorter under the high-speed condition than under the lower speed conditions. In the sitting posture, the latency was shorter when the patterns moved vertically than when they moved horizontally. In the supine posture, the latency depended neither on the physical nor on the egocentric verticality of the pattern motion. This shows that the effect of direction of moving patterns was not the same in the sitting posture and the supine posture. The results were explained by an informational difference of visual-vestibular interaction in each of these two postures.     

Implicit influence of affective postures on the perception of others: you can't show me how I feel

This study examined how one's own posture influences the perception of another's posture in a task with implicit affective information. In 2 experiments, participants assumed or viewed a body posture and then compared that posture with a viewed posture. They were not told that postures varied in affective valence: positive, negative, neutral-abstract, or neutral-meaningful. Posture affect influenced both accuracy and response time measures of posture discrimination. Participants were slower and less accurate for targets that matched an assumed posture, but only for affective postures. This pattern did not hold for matching affectively neutral postures (meaningful or not), nonmatching postures, or for purely visual comparisons. These results are consistent with both cognitive embodiment theories postulating that personal body posture influences the perception of other's postures and emotional embodiment theories postulating sensorimotor and emotional simulation processes that create correspondences between one's own and another's emotional postures. Nonetheless, these findings differ from studies finding facilitation for explicit emotional judgments of affective congruence. People use different information depending on task requirements. The assumption of an affective posture may activate simulations of personal emotional experiences that may, in turn, serve to differentiate personal posture perception from ostensibly the same posture in another person.     

Location versus distance in determining movement accuracy

In a pursuit-tracking task consisting of 100 positioning movements between targets at 5 fixed positions, target location (proximity to the boundary of the task) varied independently of movement amplitude. Eighty-seven subjects performed 12 trials of the task, with target width (at 3 levels) as a between-subject variable. A microprocessor system detected the location of the end-point of each primary movement. Movement accuracy (measured as end-point dispersion not constant error) varied with target location but not movement amplitude, while movement time varied with both factors. The effect of target width on movement accuracy was less consistent. The observed effects are discussed in terms of a mass-spring model of muscular action. It is concluded that apart from having important consequences for the design of positioning experiments, these results call into question information-processing and impulse-variability theories which implicate movement amplitude in determining movement accuracy, and support theories which emphasize target location.     

Choice of end-state comfort is dependent upon the time spent at the beginning-state and the precision requirement of the end-state

Choice of posture while grasping an object typically depends upon several factors including the time spent in that posture, what postures were held prior to choosing that posture, and the precision required by the posture. The purpose of this study was to test choice of end-state thumb-up posture based on time spent at the beginning-state and the precision requirement of the end-state. To determine choice of thumb-up based on time or precision, we varied how long a subject had to hold the beginning state before moving an object to an end location. We made end-state precision either small or large and eliminated the precision needed to stand the object up at the end of the movement. A choice between “comfort” at the beginning or precision at the end-state would be demanded by the conditions with long beginning-state hold times and high precision demands. We aimed to determine which aspect of movement was of greater importance to individuals, overall “comfort” or precision. When the requirement was to hold the initial grasp longer, and the end-target was large, we predicted that we would see more thumb-up postures adopted at the beginning state. When the final placement was small and the initial posture was not constrained, we predicted we would see thumb-up postures adopted at the end state. On average, we found that, as beginning-state grasp time increased, more individuals chose beginning-state thumb-up postures. Perhaps, not surprisingly, we found distinct individual differences within our sample. Some individuals seemed to choose beginning-state thumb-up postures nearly 100% of the time, while other individuals chose end-state thumb-up postures nearly 100% of the time. Both the time spent in a posture and its precision requirements influenced planning, but not necessarily in a systematic way.     

直立、蜷曲姿势对情绪概念加工的影响

以133名大学生为被试,采用“姿势-认知”双任务范式,通过两个实验探讨直立、蜷曲姿势对情绪概念加工的影响。实验1采用情绪词效价判断任务（浅加工）,发现无论是判断积极词语还是消极词语,姿势间的差异均不显著;实验2采用情绪词效价评定任务（深加工）,发现蜷曲比直立条件下对消极词语的评分更低,两种姿势在积极词语的评分上差异不显著。研究显示,在情绪概念加工中能够出现“蜷曲-消极”具身效应,该效应仅在认知加工程度较深的任务中出现。     

Body Posture and the Feeling of Social Closeness: An Exploratory Study in a Naturalistic Setting

Previous research has shown that body postures and body movements influence people’s attitudes, preferences and feelings. In the present study, we explored the influence of body posture on the feeling of closeness towards others and how this effect may interact with contextual variables. Study 1 was conducted in a naturalistic setting in which 127 participants observed a series of live dance sequences either standing up or remaining seated. After each sequence, participants reported the feelings elicited by the dance performance on a questionnaire. Visibility of performers’ facial expressions and background tempo were used as contextual variables. Results showed that participants who watched the performance standing up felt significantly closer to the dancers than participants who remained seated. Study 2 was carried out in a laboratory setting to explore the relationship between body posture, tempo and heart rate. Results showed a significant increase in heart rate when standing compared to when sitting and no effect of tempo. The present research demonstrates a link between body posture and social connection providing evidence that standing up strengthens the feeling of closeness to others, and showing that posture not only has an impact on self-related feelings (e.g. fear, anger, sadness) as previous research has shown, but also has an impact on feelings towards others at the base of all human social relations. The present research also suggests that heart rate may be a mediator of the effect of posture on the feeling of closeness.     

The influence of time constraints on posture choices during an end-state comfort task

People adopt comfortable postures for the end states of motor actions (end-state comfort; Rosenbaum & Jorgensen, 1992). The choice to end comfortably often elicits adoption of uncomfortable beginning states, demonstrating that a sequence of movement is planned in advance of movement onset. Many factors influence the choice of comfortable end-state postures including the greater precision and speed afforded by postures at joint angle mid-ranges (Short & Cauraugh, 1999). To date, there has been little evaluation of the hypothesis that postures are chosen based on minimizing the time spent in uncomfortable postures. The aim of this experiment was to examine how the relative time required to hold beginning and end-state postures influenced the choice of posture. Participants moved a two-toned wooden dowel from one location to another with the requirement to grasp the object and place a specified color down. Participants completed four conditions where no postures were held, only one posture was held, or both postures were held. We predicted more thumb-up postures for positions held longer regardless of whether these postures were at the end or beginning state. Results verified that the constraint of holding the initial posture led to decreased end-state comfort supporting the hypothesis that estimation of time spent in postures is an important constraint in planning. We also note marked individual differences in posture choices, particularly when the object was moved to the left.     

Two steps forward and one back: Learning to walk affects infants' sitting posture

The transition from sitting to walking is a major motor milestone for the developing postural system. This study examined whether this transition to walking impacts the previously established posture (i.e., sitting). Nine infants were examined monthly from sitting onset until 9 months post-walking. Infants sat on a saddle-shape chair either independently or with their right hand touching a stationary contact surface. Postural sway was measured by sway amplitude, variability, area, and velocity of the center of pressure trajectory. The results showed that for all the postural measures in the no-touch condition, a peak before or at walk onset was observed in all the infants. At the transition age, when peak sway occurred, infants' postural sway measures were significantly greater than at any other age. Further, infants' postural sway was attenuated by touch only at this transition. We suggest that this transient disruption in sitting posture results from a process involving re-calibration of an internal model for the sensorimotor control of posture so as to accommodate the newly emerging bipedal behavior of independent walking.     

Physical and motor skill training for children with intellectual disabilities

This study investigated the effectiveness of using special training machines for children with intellectual disabilities to strengthen their body's inner muscles and improve their ability to maintain standing posture and improve walking movement. The participants were 23 high school age boys with intellectual disabilities who had difficulties expressing greetings, and needed to be led by the hand when walking. Four special training machines were used for walking movements, for standing and walking balance, for leg-hip extension, and for ipsilateral movement in a sitting position. Each participant underwent 30 min. of training once a week over a 3-mo. period during school time. Body control ability required to perform each training exercise was improved over the training period. A significant improvement was observed in the 50-m dash, mean 10-m walk time, and 10-m obstacle course walk. The hip joint split angle showed a significant increase. Legal guardians all reported their child had "improved and/or progressed" for each of the targeted movements.     

Standing Posture on Land and at Sea

We studied the influence of ship motion on postural activity during stance, varying stance width (the distance between the feet in side-by-side stance) and the difficulty of visual tasks. Participants (experienced crewmembers) were tested on land and then on successive days on a ship at sea in mild sea states. On land, we replicated classical effects of stance width and visual task on the magnitude of postural movement. The magnitude of forces used in postural control was greater at sea than on land. Visual performance at sea was comparable to performance on land. Both stance width and visual task difficulty influenced postural activity at sea. In addition, postural activity changed over days at sea. We conclude that experienced crewmembers modulated standing posture in support of the performance of visual tasks and that such effects occurred even in mild sea states. The overall pattern of effects is compatible with the hypothesis that postural activity is modulated, in part, in support of the performance of suprapostural tasks.     

Cognitive empathy modulates the visual perception of human-like body postures without imitation

To examine the mechanism of visual perception of human-like body postures, we conducted a posture recognition task, a questionnaire survey, and the Interpersonal Reactivity Index (IRI). The majority of participants perceived the pseudo-posture as a human posture in the early stage (78%), but only approximately half of them reported the imagination of bodily movement (66%). These results suggest that the majority of observers perceive pseudo-postures as human postures in the early stage of perception, but this human posture perception does not necessarily lead to the visualisation of bodily movement. In a group of who received the pseudo posture as a human-posture regardless of the perception stages, the participants who imagined bodily movement (64%) showed significantly higher scores than those who did not on the Fantasy subscale of the IRI. Highly empathic participants are more likely to detect a kinematic relation between the pseudo-postures.     

Impact of lumbar spine posture on thoracic spine motion and muscle activation patterns

Complex motion during standing is typical in daily living and requires movement of both the thoracic and lumbar spine; however, the effects of lumbar spine posture on thoracic spine motion patterns remain unclear. Thirteen males moved to six positions involving different lumbar (neutral and flexed) and thoracic (flexed and twisted) posture combinations. The thoracic spine was partitioned into three segments and the range of motion from each posture was calculated. Electromyographical data were collected from eight muscles bilaterally. Results showed that with a flexed lumbar spine, the lower-thoracic region had 14.83° and 15.61° more flexion than the upper- and mid-thoracic regions, respectively. A flexed lumbar spine significantly reduced the mid-thoracic axial twist angle by 5.21° compared to maximum twist in the mid-thoracic region. Functional differences emerged across muscles, as low back musculature was greatest in maintaining flexed lumbar postures, while thoracic erector spinae and abdominals showed bilateral differences with greater activations to the ipsilateral side. Combined postures have been previously identified as potential injury modulators and bilateral muscle patterns can have an effect on loading pathways. Overall, changes in thoracic motion were modified by lumbar spine posture, highlighting the importance of considering a multi-segmented approach when analyzing trunk motion.     

Motion pattern and posture: Correctly assessed by calibrated accelerometers

Basic motion patterns and posture can be distinguished by multichannel accelerometry, as recently shown. A refinement of this method appeared to be desirable to further increase its effectiveness, especially to distinguish walking and climbing stairs, and body rotation during sleep. Recordings were made of 31 subjects, according to a standard protocol comprising 13 motions and postures. This recording was repeated three times with appropriate permutation. Five uni-axial sensors and three sites of placement (sternum with three axes, right and left thigh) were selected. A hierarchical classification strategy used a standard protocol (i. e., individual reference patterns) to distinguish subtypes of moving behaviors and posture. The analysis method of the actometer signals reliably detected 13 different postural and activity conditions (only 3.2 % misclassifications). A minimum set of sensors can be found for a given application; for example, a two-sensor configuration would clearly suffice to differentiate between four basic classes (sitting, standing, lying, moving) in ambulatory monitoring.     

Asymmetrical hand use in rhesus monkeys (Macaca mulatta) in tactually and visually regulated tasks

Asymmetrical hand use by rhesus monkeys (Macaca mulatta) was investigated in a series of tactually and visually guided tasks. The 1st experiment recorded manual preferences of 29 monkeys for solving a haptic discrimination task in a hanging posture. There was a left-hand population bias: 21 monkeys had a left-hand bias, 4 a right-hand bias, and 4 no bias. The 2nd experiment, 4 tasks with 23 to 51 monkeys, investigated the critical components of the 1st experiment by varying the posture (hanging, sitting, or tripedal) and the sensory requirements (tactile or visual). Posture influenced hand bias, with a population-level left-hand bias in hanging and sitting postures, but an almost symmetrical distribution in the tripedal posture. A left-hand bias was found for both sensory modalities, but the bias was stronger in the tactual tasks. Results suggest a possible right-hemisphere specialization in the rhesus for tactile, visual, or spatial processing.