Posture Representation Research Articles

Motor Planning Is Facilitated by Adopting an Action's Goal Posture: An fMRI Study

Motor planning is a hierarchical process that is typically organized around an action's goal (e.g., drinking from a cup). However, the motor plan depends not only on the goal but also on the current body state. Here, we investigated how one's own body posture interacts with planning of goal-directed actions. Participants engaged in a grasp selection (GS) task while we manipulated their arm posture. They had to indicate how they would grasp a bar when transporting it from a start to goal position and orientation. We compared situations in which one's body posture was in-congruent with the start posture and/or goal posture of the planned movement. Behavioral results show that GS took longer when one's own body state was incongruent with the goal posture of the planned movement. Correspondingly, neural activity in the intraparietal sulcus (IPS) and extrastriate body area (EBA) was modulated by congruency between the body state and the action plan. IPS was sensitive to overall congruency between body posture and action plan, while the EBA was sensitive specifically to goal posture congruency. Together, our results suggest that IPS maintains an internal state of one's own body posture, while EBA contains a representation of the goal posture of the action plan.

Efficient polygonal posture representation and action recognition

An approach to human action modelling and recognition in continuous action sequences is proposed. A star figure enclosed by a bounding convex polygon is used to effectively represent the extremities of the silhouette of a human body. Thus, human actions are recorded as a sequence of the star figure's parameters, which is then used for action modelling. To model human actions in a compact manner while characterising their spatiotemporal patterns, star figure parameters are represented by a 2D feature map, which is used and regarded as a spatiotemporal template. Experiments to evaluate the performance of the proposed framework show that it can recognise human actions in an efficient and effective manner.

Parietal cortex coding of limb posture: In search of the body-schema

Computational theories of motor control propose that the brain uses ‘forward’ models of the body to ensure accurate control of movements. Forward ‘dynamic’ models are thought to generate an estimate of the next motor state for an upcoming movement: thereby providing a dynamic representation of the current postural configuration of the body that can be utilised during movement planning and execution. We used event-related functional magnetic resonance imaging [fMRI] to investigate brain areas involved in maintaining and updating the postural representations of the upper limb that participate in the control of reaching movements. We demonstrate that the neural correlates for executing memory-guided reaching movements to unseen target locations that were defined by arm posture, are primarily within regions of the superior parietal lobule [SPL]: including an area of the medial SPL identified as the human homologue of the ‘parietal reach region’ [PRR]. Using effective connectivity analyses we show that signals that influence the BOLD response within this area originate within premotor areas of the frontal lobe, including premotor cortex and the supplementary motor area. These data are consistent with the view that the SPL maintains an up-to-date estimate of the current postural configuration of the arm that is used during the planning and execution of reaching movements.

My body in the brain: A neurocognitive model of body-ownership

Empirical research on the bodily self has only recently started to investigate how the link between a body and the experience of this body as mine is developed, maintained or disturbed. The Rubber Hand Illusion has been used as a model instance of the normal sense of embodiment to investigate the processes that underpin the experience of body-ownership. This review puts forward a neurocognitive model according to which body-ownership arises as an interaction between current multisensory input and internal models of the body. First, a pre-existing stored model of the body distinguishes between objects that may or may not be part of one's body. Second, on-line anatomical and postural representations of the body modulate the integration of multisensory information that leads to the recalibration of visual and tactile coordinate systems. Third, the resulting referral of tactile sensation will give rise to the subjective experience of body-ownership. These processes involve a neural network comprised of the right temporoparietal junction which tests the incorporeability of the external object, the secondary somatosensory cortex which maintains an on-line representation of the body, the posterior parietal and ventral premotor cortices which code for the recalibration of the hand-centred coordinate systems, and the right posterior insula which underpins the subjective experience of body-ownership. The experience of body-ownership may represent a critical component of self-specificity as evidenced by the different ways in which multisensory integration in interaction with internal models of the body can actually manipulate important physical and psychological aspects of the self.

From maps to form to space: Touch and the body schema

Evidence from patients has shown that primary somatosensory representations are plastic, dynamically changing in response to central or peripheral alterations, as well as experience. Furthermore, recent research has also demonstrated that altering body posture results in changes in the perceived sensation and localization of tactile stimuli. Using evidence from behavioral studies with brain-damaged and healthy subjects, as well as functional imaging, we propose that the traditional concept of the body schema should be divided into three components. First are primary somatosensory representations, which are representations of the skin surface that are typically somatotopically organized, and have been shown to change dynamically due to peripheral (usage, amputation, deafferentation) or central (lesion) modifications. Second, we argue for a mapping from a primary somatosensory representation to a secondary representation of body size and shape ( body form representation). Finally, we review evidence for a third set of representations that encodes limb position and is used to represent the location of tactile stimuli relative to the subject using external, non-somatotopic reference frames ( postural representations).

A real-time full body tracking and humanoid animation system

Non-intrusive human body tracking is a key issue in advanced human–computer interaction, with applications ranging from virtual reality to videoconference and telepresence. This paper describes a system for vision-based tracking of body posture. The system is explicitly designed to provide a robust yet simple and inexpensive solution to real-time body tracking through a careful choice of visual and kinematic models. Human posture representation is fully compatible with the MPEG-4 standard. Results of system application to a computer graphics scenario (animation of 3D avatars) are presented and discussed.

Force-Exertion Postures with External Bracing in Industrial Tasks: Data from an Automotive Assembly Plant

During one-handed tasks, individuals will often support their body mass using the contralateral hand or other body region. It is hypothesized that bracing postures are adopted to reduce and/or change the tasks demands, allowing the individual to assume a more optimal posture or reduce spinal loading. Accurate representation of such task postures is essential for accurate assessment of worker capability (Chaffin & Erig, 1991). It is especially critical given that the risk of injury is greatly increased when job strength requirements exceed worker capabilities (Chaffin, et al., 1978). Biomechanical analyses of supported or externally braced tasks are difficult to analyze because the upper body support is statically indeterminate. As an initial step to understanding bracing behaviors, a plant survey was conducted to investigate the prevalence of such bracing postures adopted during automotive assembly tasks. Video data from 436 occurrences of externally braced task postures from 20 automotive assembly operations were analyzed. Categorical analysis identified postural strategies associated with externally supported exertion tasks.

Shock Graph for Representation and Modeling of Posture

Skeleton transform of which the medial axis transform is the most popular has been proposed as a useful shape abstraction tool for the representation and modeling of human posture. This paper explains this proposition with a description of the areas in which skeletons could serve to enable the representation of shapes. We present algorithms for two-dimensional posture modeling using the developed simplified shock graph (SSG). The efficacy of SSG extracted feature vectors as shape descriptors are also evaluated using three different classifiers, namely, decision tree, multilayer perceptron, and support vector machine. The paper concludes with a discussion of the issues involved in using shock graphs to model and classify human postures.

Ideomotor Apraxia And Functional Ability

The impact of ideomotor apraxia (IMA) on functional ability has been a relatively neglected topic in research. This has been due to the continued focus on performance on gesture imitation and pantomime of tool-use, together with widespread acceptance of anecdotal evidence that IMA has no effect when directly manipulating objects. An increasing number of studies have shown that IMA does in fact result in increased clumsiness when handling objects and may contribute to disability in everyday life. However the effect seems relatively mild compared to the stark abnormalities on gesture imitation and pantomime. The conventional explanation for this is that the cues provided by naturalistic contexts improve retrieval of action representations, but an alternative account concerns task-specific cognitive demands. Performance on simple prehensile tasks can be successfully guided by physical affordances whereas motor tasks may be failed if they require the support of memory or problem solving ability. A central deficit in IMA may be impaired postural representation causing inability to solve the problem of how to manipulate objects where neither affordance nor memory can dictate action. However, this account still fails to explain fully the patterns of error seen on complex naturalistic tasks such as dressing. Future research needs to further our understanding of how IMA maps on to disability, which will have implications for theory building and for therapeutic intervention.

Parietal updating of limb posture: An event-related fMRI study

The posterior parietal cortex (PPC) is thought to integrate different kinds of sensory information (e.g., visual, auditory, somatosensory) to produce multiple representations of space that are each associated with different types or combinations of action; such as saccadic eye movements and reaching or grasping movements of the upper limb. Lesion studies in monkeys and in humans have shown that reaching movements to visually defined and to posturally defined targets can be dissociated from one another; indicating that different regions of the parietal cortex may code the same movement in either extrinsic (visual) or intrinsic (postural) coordinates. These studies also suggest that regions within the posterior parietal cortex play an important role in maintaining an accurate and up-to-date representation of the current postural state of the body (the body schema). We used event-related functional magnetic resonance imaging (fMRI) to investigate those brain areas involved in maintaining and updating postural (i.e., non-visual) representations of the upper limb that participate in the accurate control of reaching movements. We show that a change in the posture of the upper-limb is associated with a significant increase in BOLD activation in only one brain region—the superior parietal cortex, particularly the medial aspect (precuneus). We note that this finding is consistent with the suggestion, based upon human neurological investigations and monkey electrophysiology, that this region of the PPC may participate in the dynamic representation of the body schema, and is the most likely location for damage leading to errors in visually guided reaching to non-foveated target locations. We also note that this brain area corresponds to a region of PPC recently identified as the human homologue of the Parietal Reach Region (PRR) observed in the monkey brain that has been thought to represent reaching movements in eye-centred coordinates.

Human Posture Probability Density Estimation Based on Actual Motion Measurement and Eigenpostures

We construct human posture probability density based on actual human motion measurement. Human postures in daily life were measured for two days by having subjects wear a mechanical motion capture device. Accumulated human postures were converted to unit quaternions to guarantee the uniqueness of posture representation. To represent probability density effectively, we propose eigenpostures for posture compression and use the kernel-based reduced set density estimator (RSDE) to reduce the number of posture samples and construction of posture probability density. Before compression, unit quaternions were converted to Euclidean space by logarithmic mapping. After conversion, postures were compressed in Euclidean space. Applying constructed human posture probability density for unlikely posture detection and motion segmentation, we verified its effectiveness for many different applications.

Eye Movements Induced by Changes in the Internal Representation of Body Posture

Oculomotor responses to body rotation were investigated in subjects standing with the eyes closed. A rotatable platform was used to provide body rotation relative to the space-stationary head or upper part of the body (fixation of the head; the head and the shoulders; and the head, the shoulders, and the pelvis). A slow rotation of the body about the longitudinal axis by ±6.5° within 10–150 s evoked an illusion of the upper part of the body turning in space, while the moving footplate was perceived as stationary in space. This illusion was accompanied by marked eye movements in the direction of the illusory rotation. In subjects grasping a rigid ground-based handle, the perception of body movements corresponded to the actual rotation of body parts. In this case, the amplitude of eye movements was substantially lower. It was concluded that the eye movement pattern depends not only on the actual relative movement of the body segments but also on the perception of this movement relative to the extrapersonal space.

The role of human left superior parietal lobule in body part localization.

Electrophysiological data in primates suggest that the superior parietal lobule integrates the position of the limbs to construct complex representations of postures. Although in humans the neural basis of these mechanisms remains largely unknown, neuropsychological studies have implicated left superior parietal regions. We devised a simple functional magnetic resonance imaging paradigm aimed at exploring this hypothesis in healthy humans. Strong activation was obtained within the left but not the right superior parietal lobule, providing additional evidence that this structure may play a key role in body part localization processing.

Cutaneous afferents from human plantar sole contribute to body posture awareness.

We investigated whether the tactile information from the main supporting areas of the foot are used by the brain for perceptual purposes, namely body posture awareness and body representation in space. We applied various patterns of tactile stimulation to one or both soles of unmoving and blindfolded subjects by a 60 micro-vibrator tactile matrix set in a force platform. The perceptual effects of the stimulation were assessed through a 3D joystick handled by the subjects. All subjects reported illusory perceptions of whole-body leaning. Both orientation and amplitude of these perceptions depended on the stimulation pattern. Additional kinesthetic illusions sometimes occurred along the longitudinal axis of the body. We conclude that foot sole input contributes to the coding and the spatial representation of body posture.

Compact Representation of Human Postures for Data Broadcasting

Compact Representation of Human Postures for Data Broadcasting

Ipsilesional deficits during fast diadochokinetic hand movements following unilateral brain damage

Impaired sensorimotor function of the hand ipsilateral to a unilateral brain lesion has been reported in a variety of motor tasks; however, elementary diadochokinetic movements, such as tapping with the index finger, seem to be preserved in chronic-lesion patients. Three different diadochokinetic movements (forearm diadochokinesis, hand tapping (HT) and finger tapping (FT)) were tested in patients with left brain damage (LBD) and right brain damage (RBD) and control subjects. Movements were measured three-dimensionally and the kinematics of joint angles were analyzed. While the patients’ measures of movement speed and symmetry appeared normal, detailed kinematic analysis revealed clear deficits in several measures of movement variability, which reflected decreased regularity of the alternating movement cycles. This impairment was greater in LBD patients and tended to be greater during forearm diadochokinesis. The necessity of ipsilateral control in addition to dominant, contralateral control, especially during left hand and more complex or more proximal manual tasks may account for these findings. In addition, the role of apraxia (defined by impairments during the imitation of gestures) in the performance deficits of LBD patients was also assessed. Although, some performance decrements were associated with the presence of apraxia, these were different from the group findings and restricted to the two tapping tasks. Thus, although apraxia may have caused deficits in establishing dynamic representations of the elementary postures in conditions of high speed and low complexity, the disturbances during diadochokinetic movements must for the most part be attributed to more motor-related deficits of ipsilateral sensorimotor control, which are particularly apparent when the motor dominant left hemisphere is affected. The absence of clear correlations between performance deficits and lesion characteristics suggests that a distributed network is involved in this ipsilateral control.

Ideomotor apraxia, visuomotor control and the explicit representation of posture

Ideomotor apraxia is normally viewed as a disorder of the representation or execution of action. However, the evidence from gesture imitation is that apraxic patients are unable to reproduce the final posture of a gesture but may not show abnormality in movement kinematics. This supports a hypothesis that impaired gesture imitation is due to a deficit in a conceptual representation of body posture rather than indicating a disorder specific to action control. The present study evaluated whether other aspects of apraxic behaviour might also be most consistent with a deficit in the representation of posture. Patients with left hemisphere damage and apraxia on gesture imitation had difficulty in reproducing a series of actions due to failure to adopt the required configuration of the hand whereas there was no consistent reduction in speed of response once the actions had been learned. They also tended to use an abnormal, clumsy grasp when using a spoon but this dissociated from accurate performance on other tests of manual dexterity where there was less scope for variation in configuration of the hand. These data suggest that the most common deficit in ideomotor apraxia is impaired ability to perform tasks where the goal is to reproduce or adopt complex hand configurations and that impaired execution of some types of action is secondary to this problem. This is consistent with a role for the human left parietal lobe in providing an explicit representation of posture which is used to guide some actions and to supplement a more primitive system of direct visuomotor control.

Rectifying postures reconstructed from joint angles to meet constraints

Postures are often described and modeled using angles between body segments rather than joint coordinates. Models can be used to predict these angles as a function of anthropometry and postural requirements. Postural representation, however, requires the joint coordinates. The use of conventional forward kinematics to derive joint coordinates from predicted angles may violate task constraints, such as the placement of a hand on a target or a foot on a pedal. Errors arise because the anthropometry or other motion characteristics of a subject, for which the prediction is to be made, may differ from the data from which the prediction model was derived. We describe how to rectify model-predicted postures to exactly satisfy such task constraints. We require that the model used for predicting the angles also produce estimates of the variation in these predictions. We show how to alter the initial angle predictions, with the amount of perturbation at each angle dependent on the accuracy of its estimation, so as to exactly satisfy the joint coordinate constraints. Finally, we show in an empirical example that this correction usually produces better overall predictions of posture than those obtained initially.

Cocoon Spinning Behavior in the Silkworm, Bombyx mori : Comparison of Three Strains Constructing Different Cocoons in Shape

The spinning behavior of the silkworm, Bombyx mori, was recorded on videotapes from two angles and analysed by three dimentional computer graphics using the Japanese (J. 124), Chinese (C.124) and their hybrid (J.124 × C.124) strains. These strains constructed typical peanut-shaped, spherical and ellipsoidal cocoons, respectively. Linear representation of the spinning posture revealed that larvae fixed the posterior half of the larval body (6th to 13th segment) and spun silk moving their anterior half (1st to 5th segment) for the most spinning period in all strains used. Little difference was observed in the average spinning speed among them. The Japanese strain spun primarily in a S-letter posture and changed its direction frequently. The larva of Chinese strain often assumed a C-letter posture and showed directionchanging behavior with comparatively lower frequency. The hybrid larva threw the head back largely in an U-letter shape during most of the spinning period and showed cocoon expansion behaviors most frequently. The cocoon expansion behavior occurred mainly at both ends of the peanut-shaped cocoon (J.124), at the center part of the spherical cocoon (C.124) and at both shoulders in the ellipsoidal cocoon of the hybrid strain. Thus, there exist strain-specific features in the spinning behavior, and it is suggested that the main behavioral factors affecting cocoon shape formation are the spinning posture and the cocoon expansion behavior during spinning.

Representation of passive hindlimb postures in cat spinocerebellar activity.

1. We report here about the modulation of dorsal spinocerebellar tract (DSCT) activity by limb posture. In principle, DSCT activity could represent limb position in one of several ways. According to a classical notion of DSCT function, DSCT activity might be expected to correlate with changes in individual joint angles. However, given the evidence for extensive polysynaptic convergence onto DSCT units, it is reasonable to propose that DSCT activity represents more global variables such as the orientation of limb segments or the length and orientation of the whole limb. 2. In six anesthetized cats we recorded the activity of 96 antidromically identified DSCT neurons while a robot arm passively positioned the left hindfoot in 20 positions distributed in the sagittal plane, holding each position for 8 s. For each position we measured the joint angles, limb segment angles, and the length and orientation of the limb axis (defined as the line connecting the hip joint to the hindpaw). We used regression statistics to quantify 1) possible relationships among geometric variables of the hindlimb and 2) relationships between DSCT firing rate and limb variables. 3. First, we found a statistically significant relationship among the joint angles that could be described by a covariance plane accounting for approximately 70 percent of the total variance. Thus the 3 degrees of freedom represented by the joint angles in the sagittal plane are effectively reduced to only 2 by the coupling between joints. This finding resembles that described for the behaving cat during stance. However, the correlation between the hip and ankle angles in the passively displaced hindlimb was just the opposite of that observed during active stance. Moreover, we observed that the length and the orientation of the limb axis is determined simply by a linear combination of the three joint angles. 4. Most of the DSCT neurons (82 of 96) were significantly modulated by changes in foot position (1-way analysis of variance, P < 0.001). For those cells, we explored systematically how their activity was related to limb geometric variables. We found mostly linear relationships between individual joint or limb segments angles and DSCT firing rates. However, although these relationships were statistically significant, the random variance was often quite high. Moreover, approximately 70% of the cells were modulated by more than one joint or limb segment angle, suggesting that a model incorporating global geometric variables might explain a larger fraction of the variance in the neural data. 5. Consequently we tested how well DSCT activity was modulated by the length and the orientation of the limb axis with the use of a linear regression model with length and orientation (or the equivalent linear combination of joint angles) as predictors. We found that this model explained a larger fraction of the variability in the firing pattern of nearly every modulated cell than did any of the single joint models tested. 6. We also attempted to account for the effect of the mechanical joint covariance on this result by accounting for correlated independent variables in the analysis. We used a regression model incorporating all three joint or limb segment angles and performed a backward elimination of insignificant or redundant variables. The result was that 67% of the neurons were independently modulated by at least two joint angles, indicating that the modulation did not necessarily reflect the biomechanical constraint of joint angle covariation, but rather a central convergence of sensory information from more than a single joint. 7. From these results we conclude that the firing rates of a majority of DSCT neurons encode the position of the hindfoot relative to the hip joint.(ABSTRACT TRUNCATED)