Hand Model Research Articles

Estimating Human Upper Limb Impedance Parameters From a State-of-the-Art Computational Neuromusculoskeletal Model.

The human neuro-musculoskeletal system constantly deploys passive (e.g., posture adjustment) and active (e.g., muscle co-contraction) control strategies to regulate upper limb impedance and stability while interacting with the outside world. Upper limb impedance has been assessed through in vivo experiments and model-based simulations. The experiments are practically limited to small samples of able-bodied subjects and few limb postures, and model-based approaches have mostly used simplified upper limb models. Our objective was to develop and validate a computational approach to estimate upper limb impedance parameters - stiffness, viscosity, and inertia - at the endpoint (i.e., hand) using a neuromusculoskeletal model with realistic geometry. We added a planar manipulandum to an existing upper limb model implemented in OpenSim (version 3.3) and used contact modeling to attach the manipulandum's handle to the musculoskeletal model's hand. The hand was placed at several locations lateral to the shoulder joint along anterior/posterior and medial/lateral axes. At each location, during forward dynamics simulations, the manipulandum applied small perturbations to the hand in eight different directions. The spatial variation of the computed, model-based impedance parameters was similar to that of experimentally measured impedance parameters. However, the overall size of the stiffness and viscosity components was larger in the model than from experiments.Clinical Relevance- Computational modeling and simulations can estimate upper limb impedance properties to complement and overcome the limitations of experiments, especially for clinical populations. The computational approach could ultimately inform new interventions and devices to restore limb stability in people with shoulder disabilities.

12- to 14-month-olds expect unconstrained agents to act efficiently: Event-related potential (ERP) evidence from the head-touch paradigm.

Behavioral research has shown that 12- but not 9-month-olds imitate an unusual and inefficient action (turning on a lamp with one's forehead) more when the model's hands are free. Rational-imitation accounts suggest that infants evaluate actions based on the rationality principle, that is, they expect people to choose efficient means to achieve a goal. Accordingly, infants' expectations should be violated when observing inefficient actions. However, this has yet to be clearly tested. Here, we conducted three electrophysiological experiments to assess infants' neural indices of violation of expectation (VOE) when observing hand- and head-touch actions. We presented infants with video sequences showing a model whose hands were either free (Experiments 1 and 3) or restrained (Experiment 2). Subsequent images depicted a person turning on a lamp or a toy soundbox using her hand or head. We analyzed the Negative central (Nc) component, associated with the amount of attentional engagement, and the N400 component, reflecting semantic violations. In line with rational-imitation accounts, results revealed that 12- to 14-month-olds (Experiment 1) but not 9-month-olds (Experiment 3) were surprised while observing an inefficient, hands-free, head touch, as indicated by an increased Nc amplitude and an N400-like component. In contrast, infants did not show differences in our measures of VOE between head- and hand-touch outcomes when the model's hands were restrained (Experiment 2). Thus, we suggest that 12- to 14-month-olds incorporate the action context when evaluating action outcomes. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Motor imagery alone drives corticospinal excitability during concurrent action observation and motor imagery

We studied the motor simulation processes involved in concurrent action observation and motor imagery (AO+MI) using motor evoked potentials induced by transcranial magnetic stimulation. During congruent AO+MI, participants were shown videos of a model's hand performing rhythmical finger movements, and they imagined moving the same finger of their own hand in synchrony with the observed finger. During incongruent AO+MI, the imagery task involved a different finger from the observed one. As expected, congruent AO+MI yielded robust facilitatory effects, relative to baseline, only in the effector involved in the task. Incongruent AO+MI produced equally pronounced effects in the effector that was engaged in MI, whilst no corticospinal facilitation was found for the effector corresponding to the observed action. We further replicated that engaging in pure AO without MI does not produce reliable effects. These results do not support the proposal that observed and imagined action are both simulated at the level of the primary motor cortex. Rather, motor imagery alone can sufficiently explain the observed effects in both AO+MI conditions. This bears clear implications for the application of AO+MI procedures in sport and neurorehabilitation.

Reduced Mu Power in Response to Unusual Actions Is Context-Dependent in 1-Year-Olds.

During social interactions infants predict and evaluate other people’s actions. Previous behavioral research found that infants’ imitation of others’ actions depends on these evaluations and is context-dependent: 1-year-olds predominantly imitated an unusual action (turning on a lamp with one’s forehead) when the model’s hands were free compared to when the model’s hands were occupied or restrained. In the present study, we adapted this behavioral paradigm to a neurophysiological study measuring infants’ brain activity while observing usual and unusual actions via electroencephalography. In particular, we measured differences in mu power (6 – 8 Hz) associated with motor activation. In a between-subjects design, 12- to 14-month-old infants watched videos of adult models demonstrating that their hands were either free or restrained. Subsequent test frames showed the models turning on a lamp or a soundbox by using their head or their hand. Results in the hands-free condition revealed that 12- to 14-month-olds displayed a reduction of mu power in frontal regions in response to unusual and thus unexpected actions (head touch) compared to usual and expected actions (hand touch). This may be explained by increased motor activation required for updating prior action predictions in response to unusual actions though alternative explanations in terms of general attention or cognitive control processes may also be considered. In the hands-restrained condition, responses in mu frequency band did not differ between action outcomes. This implies that unusual head-touch actions compared to hand-touch actions do not necessarily evoke a reduction of mu power. Thus, we conclude that reduction of mu frequency power is context-dependent during infants’ action perception. Our results are interpreted in terms of motor system activity measured via changes in mu frequency band as being one important neural mechanism involved in action prediction and evaluation from early on.

Embodied hands

Humans move their hands and bodies together to communicate and solve tasks. Capturing and replicating such coordinated activity is critical for virtual characters that behave realistically. Surprisingly, most methods treat the 3D modeling and tracking of bodies and hands separately. Here we formulate a model of hands and bodies interacting together and fit it to full-body 4D sequences. When scanning or capturing the full body in 3D, hands are small and often partially occluded, making their shape and pose hard to recover. To cope with low-resolution, occlusion, and noise, we develop a new model called MANO ( hand Model with Articulated and Non-rigid defOrmations ). MANO is learned from around 1000 high-resolution 3D scans of hands of 31 subjects in a wide variety of hand poses. The model is realistic, low-dimensional, captures non-rigid shape changes with pose, is compatible with standard graphics packages, and can fit any human hand. MANO provides a compact mapping from hand poses to pose blend shape corrections and a linear manifold of pose synergies. We attach MANO to a standard parameterized 3D body shape model (SMPL), resulting in a fully articulated body and hand model (SMPL+H). We illustrate SMPL+H by fitting complex, natural, activities of subjects captured with a 4D scanner. The fitting is fully automatic and results in full body models that move naturally with detailed hand motions and a realism not seen before in full body performance capture. The models and data are freely available for research purposes at http://mano.is.tue.mpg.de.

Eye movements may cause motor contagion effects.

When a person executes a movement, the movement is more errorful while observing another person's actions that are incongruent rather than congruent with the executed action. This effect is known as "motor contagion". Accounts of this effect are often grounded in simulation mechanisms: increased movement error emerges because the motor codes associated with observed actions compete with motor codes of the goal action. It is also possible, however, that the increased movement error is linked to eye movements that are executed simultaneously with the hand movement because oculomotor and manual-motor systems are highly interconnected. In the present study, participants performed a motor contagion task in which they executed horizontal arm movements while observing a model making either vertical (incongruent) or horizontal (congruent) movements under three conditions: no instruction, maintain central fixation, or track the model's hand with the eyes. A significant motor contagion-like effect was only found in the 'track' condition. Thus, 'motor contagion' in the present task may be an artifact of simultaneously executed incongruent eye movements. These data are discussed in the context of stimulation and associative learning theories, and raise eye movements as a critical methodological consideration for future work on motor contagion.

Simulation of Surfactant/Polymer Floods With a Predictive and Robust Microemulsion Flash Calculation

Summary A compositional reservoir simulator that uses a predictive microemulsion phase-behavior model is essential for accurate estimation of oil recovery from surfactant/polymer (SP) floods. Current chemical-flooding simulators, however, use Hand's model (Hand 1939) for phase-behavior calculation. Hand's model can reasonably fit a limited set of experimental data, such as those of a salinity scan, but because it is empirical, it cannot predict phase behavior outside the matched data set. Hydrophyllic/lypophyllic difference (HLD) and net-average-curvature (NAC) equation of state (EOS) (Acosta et al. 2003) has shown great performance for tuning and prediction of experimental data. In this paper, the EOS model with the extension to two-phase regions has been incorporated for the first time into UTCHEM (2000) and our in-house general-purpose compositional simulator, PennSim (2013). All Winsor regions (Type II−, II+, III, and IV) are modeled by use of a consistent physics-based EOS model without the need for Hand's approach. The new simulator is therefore able to account correctly for gridblock properties, which can vary temporally and spatially, and significantly improve the modeling of phase behavior and oil recovery. The results show excellent agreement between UTCHEM and PennSim both in composition space and for composition/saturation profiles for the 1D simulation. The effects of varying pressure, temperature, equivalent alkane carbon number (EACN), and salinity on recoveries are demonstrated also in 1D simulations.

Social perception: How do 6-month-old infants look at pointing gestures?

The study explored 6-month-old infants’ ability to follow a pointing gesture in a dynamic social context. The infants were presented with a video of a model pointing to one of two toys. The pointing gesture was performed either normally (with arm and hand pointing at the same direction), with a stick, or the model's arm and hand pointing in different directions (at different toys). The results indicate that infants at this age reliably followed pointing performed normally.

Observational Learning and Pain-Related Fear: Exploring Contingency Learning in an Experimental Study Using Colored Warm Water Immersions

This study investigated observational learning of pain-related fear and subsequent extinction after first-hand exposure to the feared stimulus. Moreover, the specific contingencies that are learned when observing others in pain were explored. A differential fear-conditioning paradigm was used, showing video models displaying either a painful (CS+ color; aversively conditioned stimulus) or a neutral (CS− color; neutrally conditioned stimulus) facial expression in the presence of a colored warm water task (WWT; observation phase). In 1 condition (open WWT cover), the model's hand was immersed in the colored liquid, while in the other condition (closed WWT cover), no contact was displayed between the model and the liquid. During exposure, participants subsequently immersed their own hand into each WWT with equal temperatures. Results revealed successful acquisition of pain-related fear. Participants with higher levels of pain catastrophizing, intolerance of uncertainty, trait fear of pain, or dispositional empathy were more prone to develop pain-related fear. Pain-related fear extinguished quickly after direct exposure to both WWTs. Contingencies between the color of the WWT and either the painful facial expressions or the assumed properties of the colored liquid were learned in both conditions. Clinical implications and limitations of the current study are discussed, providing avenues for future research in observational learning of pain-related fear. PerspectivePain-related fear promotes the development as well as the continuation of chronic pain. A better understanding of the acquisition and extinction of this fear may help to improve pain treatment programs. Furthermore, we intended to identify individuals who are more prone to develop pain-related fear.

A platform for dynamic simulation and control of movement based on OpenSim and MATLAB

Numerical simulations play an important role in solving complex engineering problems and have the potential to revolutionize medical decision making and treatment strategies. In this paper, we combine the rapid model-based design, control systems and powerful numerical method strengths of MATLAB/Simulink with the simulation and human movement dynamics strengths of OpenSim by developing a new interface between the two software tools. OpenSim is integrated with Simulink using the MATLAB S-function mechanism, and the interface is demonstrated using both open-loop and closed-loop control systems. While the open-loop system uses MATLAB/Simulink to separately reproduce the OpenSim Forward Dynamics Tool, the closed-loop system adds the unique feature of feedback control to OpenSim, which is necessary for most human movement simulations. An arm model example was successfully used in both open-loop and closed-loop cases. For the open-loop case, the simulation reproduced results from the OpenSim Forward Dynamics Tool with root mean square (RMS) differences of 0.03° for the shoulder elevation angle and 0.06° for the elbow flexion angle. MATLAB's variable step-size integrator reduced the time required to generate the forward dynamic simulation from 7.1s (OpenSim) to 2.9s (MATLAB). For the closed-loop case, a proportional–integral–derivative controller was used to successfully balance a pole on model's hand despite random force disturbances on the pole. The new interface presented here not only integrates the OpenSim and MATLAB/Simulink software tools, but also will allow neuroscientists, physiologists, biomechanists, and physical therapists to adapt and generate new solutions as treatments for musculoskeletal conditions.

Seeing touch and pain in a stranger modulates the cortical responses elicited by somatosensory but not auditory stimulation

Viewing other's pain inhibits the excitability of the motor cortex and also modulates the neural activity elicited by a concomitantly delivered nociceptive somatosensory stimulus. As the neural activity elicited by a transient nociceptive stimulus largely reflects non nociceptive-specific, multimodal neural processes, here we tested, for the first time, whether the observation of other's pain preferentially affects the brain responses elicited by nociceptive stimulation, or instead similarly modulates those elicited by stimuli belonging to a different sensory modality. Using 58-channel electroencephalography (EEG), we recorded the cortical responses elicited by laser and auditory stimulation during the observation of videoclips showing either noxious or non-noxious stimulation of a stranger's hand. We found that the observation of other's pain modulated the cortical activity consisting in an event-related desynchronization in the β band (β ERD), and elicited by nociceptive laser stimuli, but not by auditory stimuli. Using three different source analysis approaches, we provide converging evidence that such modulation affected neural activity in the contralateral primary sensorimotor cortex. The magnitude of this modulation correlated well with a subjective measure of similarity between the model's hand and the onlooker's representation of the hand. Altogether, these findings demonstrate that the observation of other's pain modulates, in a somatosensory-specific fashion, the cortical responses elicited by nociceptive stimuli in the sensorimotor cortex contralateral to the stimulated hand.

Evaluating the empirical evidence for the two-stage-model of infant imitation. A commentary on Paulus, Hunnius, Vissers, and Bekkering (2011)

GENERAL COMMENTARY article Front. Psychol., 21 November 2012Sec. Developmental Psychology Volume 3 - 2012 | https://doi.org/10.3389/fpsyg.2012.00512

The Development of Rational Imitation in 9- and 12-Month-Old Infants.

Studies on rational imitation have provided evidence for the fact that infants as young as 12 months of age engage in rational imitation. However, the developmental onset of this ability is unclear. In this study, we investigated whether 9- and 12-month-olds detect voluntary and implicit as well as nonvoluntary and explicit constraints in the head touch task. Three groups of infants watched video sequences, which displayed a person illuminating a lamp using the head. The hands of the model were either free, occupied by voluntarily holding a blanket, or nonvoluntarily restrained by being tied to the table. An additional control group of infants watched the model turning on the lamp by using the hand. Given that the majority of infants imitated the head touch when the model's hands were free, there was evidence for rational imitation in comparison to the condition in which the model's hands were tied to the table, but not in comparison to the condition in which the hands were occupied by holding a blanket. Nine-month-olds showed no differences in their behavior according to the condition. These findings clarify the onset of rational imitation by showing that 12-month-olds (but not 9-month-olds) take into account a situational constraint only when the constraint is nonvoluntary and explicit.

Freezing or escaping? Opposite modulations of empathic reactivity to the pain of others

Perceiving pain in others may induce the covert simulation of both sensory and emotional components of others' pain experience. Previous transcranial magnetic stimulation (TMS) studies have investigated the motor counterpart of this resonant mapping by showing suppression of motor-evoked potentials (MEPs) during the observation of a needle entering body parts of another person. Here we explored whether MEPs recorded from an onlooker's hand (e.g., the right hand, TMS to the left motor cortex) are differentially influenced by the observation of painfully stimuli delivered to the same (right) or the opposite (left) hand in a model. Congruency between observed (model) and recorded (onlooker) hand brought about a reduction of MEPs amplitude. This resonant inhibitory response in the onlooker was specific for the muscle penetrated in the model. In contrast, observing pain on the model's hand opposite to that from which MEPs were recorded brought about a generalized increase of hand corticospinal excitability. Corticospinal inhibition and facilitation effects were comparable in the two hemispheres and specific for the corresponding and opposite hand. Results suggest that observing pain in another person's hand automatically induces the covert simulation of potentially adaptive freezing and avoidance responses in the onlooker's corticospinal system.

Action anticipation and motor resonance in elite basketball players

We combined psychophysical and transcranial magnetic stimulation studies to investigate the dynamics of action anticipation and its underlying neural correlates in professional basketball players. Athletes predicted the success of free shots at a basket earlier and more accurately than did individuals with comparable visual experience (coaches or sports journalists) and novices. Moreover, performance between athletes and the other groups differed before the ball was seen to leave the model's hands, suggesting that athletes predicted the basket shot's fate by reading the body kinematics. Both visuo-motor and visual experts showed a selective increase of motor-evoked potentials during observation of basket shots. However, only athletes showed a time-specific motor activation during observation of erroneous basket throws. Results suggest that achieving excellence in sports may be related to the fine-tuning of specific anticipatory 'resonance' mechanisms that endow elite athletes' brains with the ability to predict others' actions ahead of their realization.

The pain of a model in the personality of an onlooker: Influence of state-reactivity and personality traits on embodied empathy for pain

The study of inter-individual differences at behavioural and neural levels represents a new avenue for neuroscience. The response to socio-emotional stimuli varies greatly across individuals. For example, identification with the feelings of a movie character may be total for some people or virtually absent for others. Inter-individual differences may reflect both the on-line effect (state) of the observed stimuli and more stable personal characteristics (trait). Here we show that somatomotor mirror responses when viewing others' pain are modulated by both state- and trait-differences in empathy. We recorded motor-evoked potentials (MEPs) induced by Transcranial Magnetic Stimulation (TMS) in healthy individuals observing needles penetrating a model's hand. We found a reduction of corticospinal excitability that was specific for the muscle that subjects observed being penetrated. This inhibition correlated with sensory qualities of the pain ascribed to the model. Moreover, it was greater in subjects with high trait-cognitive empathy and lower in subjects with high trait-personal distress and in those with high aversion for the observed movies. Results indicate that somatomotor responses to others' pain are influenced by specific onlookers' personality traits and self-oriented emotional reactions. Our findings suggest that multiple distinct mechanisms shape mirror mapping of others' pain.

Action observation supports effector-dependent learning of finger movement sequences

Practising a motor skill can result in effector-dependent learning (learning that does not transfer from the set of muscles used in training to a new set of muscles). Proceeding from neurophysiological evidence of motor activation during action observation, this study asked whether observational learning, learning through observation of skilled performance, can also be effector-dependent. Adult human participants observed a model's right hand as the model responded to an eight-item sequence in a serial reaction time (SRT) task. Their sequence learning was then compared in two tests with that of controls who had observed the model's right hand responding to random targets during training. All participants performed the SRT task with their right hand in the first test and with their left hand in the second. Evidence of observational learning was obtained in the right hand test but not in the left hand test. This implies that sequence learning based on observation of right hand performance did not transfer to the left hand, and therefore that observational learning can support effector-dependent learning of finger movement sequences. A second experiment used the same procedure to assess learning by a group of participants who observed a sequence of response locations only. This group did not observe the model's responses. Results suggested that action observation was necessary for the effector-dependent observational learning demonstrated in Experiment 1.

Erratum and Addenda: Wave Equations from Laplacian and D'Alembertian Quantum Potentials [Phys. Essays11, 600 (1998)] and Realistic Fluid Models forhand for de Broglie Waves, and Wave Equations from the Quantum Potentials [Phys. Essays11, 166 (1998)

Erratum and Addenda: Wave Equations from Laplacian and D'Alembertian Quantum Potentials [Phys. Essays<b>11</b>, 600 (1998)] and Realistic Fluid Models for<i>h</i>and for de Broglie Waves, and Wave Equations from the Quantum Potentials [Phys. Essays<b>11</b>, 166 (1998)

Rheological Properties of Liquid Crystalline Solutions of Poly‐p‐Phenyleneterphthalamide in Sulfuric Acid

The steady state shear and linear viscoelastic properties of both isotropic and liquid crystalline solutions of the rigid chain polymer poly‐p‐phenyleneterephthalamide in sulfuric acid have been determined. Both the primary normal stress coefficient and the linear viscoelastic properties show the same characteristic concentration behavior as does the viscosity. The unique rheological properties of the anisotropic phase can be attributed to the formation of a suspension of highly ordered regions in a matrix of isotropic fluid. The rheological properties were compared against the Bird‐Carreau model and Hand's anisotropic fluid theory. Remarkably good agreement was found between the Bird‐Carreau model and data especially at high shear rates. This suggested that at high shear rates very little difference may exist between anisotropic and isotropic phases. Hand's model was more applicable to solutions which were only slightly anisotropic.

Constitutive equations in suspension mechanics. Part 1. General formulation

Neither the phenomenological nor the structural approach to the determination of constitutive equations has yet shown itself to be capable of producing useful and predictive descriptions of the majority of technologically important complex fluids. In the present paper we explore the suggestion that significant progresscanbe made when these two complementary approaches to rheology are combined. For this initial study we restrict our attention to materials which can be modelled as a suspension of particles in a Newtonian fluid, thereby including most polymer solutions while excluding polymer melts. By applying phenomenological techniques to the basic formulation of suspension mechanics we are able to deduce a common simplified constitutive model for all suspension-like materials and to reveal its physical origin. The present analysis demonstrates that the constitutive model of Hand (1962), involving a single second-order tensor, is not sufficiently general for a rigorous description of the majority of suspension-like materials. Consideration of the constitutive forms for the limiting cases of near-equilibrium and strongly non-equilibrium microstructure suggests, however, that Hand's model may provide a reasonable approximation to the exact constitutive behaviour which is useful over the whole range of flow strengths.