Human Sensorimotor System Research Articles

Integration of haptics and vision in human multisensory grasping

Grasping actions are directed not only toward objects we see but also toward objects we both see and touch (multisensory grasping). In this latter case, the integration of visual and haptic inputs improves movement performance compared to each sense alone. This performance advantage could be due to the integration of all the redundant positional and size cues or to the integration of only a subset of these cues. Here we selectively provided specific cues to tease apart how these different sensory sources contribute to visuo-haptic multisensory grasping. We demonstrate that the availability of the haptic positional cue together with the visual cues is sufficient to achieve the same grasping performance as when all cues are available. These findings provide strong evidence that the human sensorimotor system relies on non-visual sensory inputs and open new perspectives on their role in supporting vision during both development and adulthood.

Anthropological Information About a Message Variability

The article represents a particular case in the field of the theory of a message encoding and decoding when the message is transmitted from a transmitter to a receiver. In this case human plays a role of the transmitter and receiver. From the positions of the theory of coding and the theory of pattern recognition, considers the phenomenon of anthropological similarity in the anatomical structure of the human sensory-motor system. There is illustration of the importance of the topological similarity of the transmitter and receiver as a source of additional information on the example of an anthropological (species) similarity of the auditory and articulation systems. The results of experiments support the idea the receiver receives additional information or anthropological information about the message, which is decoded not from the message, but from a physical structure of the receiver. Such a transfer is possible with reference to information about human means, articulations, facial expressions and pantomimic poses. It is concluded, in order to convey the knowledge, the physical structure of the information carrier about this knowledge must be the same for the transmitter of the message and the receiver; in other cases, genesis of this additional information a priori impossible.

Electrocorticographic dissociation of alpha and beta rhythmic activity in the human sensorimotor system.

This study uses electrocorticography in humans to assess how alpha- and beta-band rhythms modulate excitability of the sensorimotor cortex during psychophysically-controlled movement imagery. Both rhythms displayed effector-specific modulations, tracked spectral markers of action potentials in the local neuronal population, and showed spatially systematic phase relationships (traveling waves). Yet, alpha- and beta-band rhythms differed in their anatomical and functional properties, were weakly correlated, and traveled along opposite directions across the sensorimotor cortex. Increased alpha-band power in the somatosensory cortex ipsilateral to the selected arm was associated with spatially-unspecific inhibition. Decreased beta-band power over contralateral motor cortex was associated with a focal shift from relative inhibition to excitation. These observations indicate the relevance of both inhibition and disinhibition mechanisms for precise spatiotemporal coordination of movement-related neuronal populations, and illustrate how those mechanisms are implemented through the substantially different neurophysiological properties of sensorimotor alpha- and beta-band rhythms.

Achieving Neural Compatibility With Human Sensorimotor Control in Prosthetic and Therapeutic Devices

Prosthetic and therapeutic devices have been developed to ameliorate the quality of daily living for people with amputation or neurological disorders. However, many of them fall short of functional benefits, and therefore, are frequently rejected by users due to awkward control, or no awareness of interaction during tasks. Traditional wisdom in the design of prosthetic and therapeutic devices may have emphasized the need to provide users with apparatus that replace or assist motor ability. Rather, the notion to achieve neural compatibility with the existing sensorimotor system has not been well recognized. We argue that providing biomimetic control and sensing capacity to prosthetic and therapeutic devices can enhance their neural compatibility, and therefore, can yield greater functionality in performing activities of daily lives, or in rehabilitation training. In this paper, the authors will present a range of neural technologies that may allow implementation of biomimetic sensorimotor control, including natural sensory feedback, neuromuscular like compliant control, natural module of synergy-based control, as well as advanced neural signal processing techniques. Based on the evidence in our research and in literature, we propose that achieving neural compatibility with the existing human sensorimotor system should be the ultimate goal of prosthetic and therapeutic devices.

Damping Perception During Active Ankle and Knee Movement.

The mechanical impedance of the leg governs many important aspects of locomotion, including energy storage, transfer, and dissipation between joints. These mechanical properties, including stiffness and damping, have been recently quantified at the ankle joint during walking. However, little is known about the human ability to sense changes in impedance. Here, we investigate the ability to detect small changes in damping coefficients when interacting with a mechanical system coupled to the ankle or knee joint. Using a psychophysical experiment (adaptive, weighted staircase method) and an admittance-controlled dynamometer, we determined the 75% minimum detectable change by tasking subjects to compare the damping values of different virtual spring-mass-damper systems. The Weber fraction for damping coefficient ranged from 12% to 31%, with similar performance across the ankle and knee. Damping perception performance was similar to previous stiffness perception results, suggesting that both the stiffness and damping of the environment are important for the human sensorimotor system and motivating further investigation on the role of damping in biomechanics, motor control, and wearable robotic technologies.

An Uncontrolled Manifold Analysis of Arm Joint Variability in Virtual Planar Position and Orientation Telemanipulation.

In teleoperated robot-assisted tasks, the user interacts with manipulators to finely control remote tools. Manipulation of robotic devices, characterized by specific kinematic and dynamic proprieties, is a complex task for the human sensorimotor system due to the inherent biomechanical and neuronal redundancies that characterize the human arm and its control. We investigate how master devices with different kinematics structures and how different task constraints influence users capabilities in exploiting arm redundancy. A virtual teleoperation workbench was designed and the arm kinematics of seven users was acquired during the execution of two planar virtual tasks, involving either the control of position only or position-orientation of a tool. Using the uncontrolled manifold analysis of arm joint variability, we estimated the logarithmic ratio between the task irrelevant and the task relevant manifolds ( Rv). The Rv values obtained in the position-orientation task were higher than in the position only task, while no differences were found between the master devices. A modulation of Rv was found through the execution of the position task and a positive correlation was found between task performance and redundancy exploitation. Users exploited additional portions of arm redundancy when dealing with the tool orientation. The Rv modulation seems influenced by the task constraints and by the users possibility of reconfiguring the arm position. This paper advances the general understanding of the exploitation of arm redundancy in complex tasks, and can improve the development of future robotic devices.

Visuomotor coordination and cortical connectivity of modular motor learning.

The ability to transfer sensorimotor skill components to new actions and the capacity to use skill components from whole actions are characteristic of the adaptability of the human sensorimotor system. However, behavioral evidence suggests complex limitations for transfer after combined or modular learning of motor adaptations. Also, to date, only behavioral analysis of the consequences of the modular learning has been reported, with little understanding of the sensorimotor mechanisms of control and the interaction between cortical areas. We programmed a video game with distorted kinematic and dynamic features to test the ability to combine sensorimotor skill components learned modularly (composition) and the capacity to use separate sensorimotor skill components learned in combination (decomposition). We examined motor performance, eye-hand coordination, and EEG connectivity. When tested for integrated learning, we found that combined practice initially performed better than separated practice, but differences disappeared after integrated practice. Separate learning promotes fewer anticipatory control mechanisms (depending more on feedback control), evidenced in a lower gaze leading behavior and in higher connectivity between visual and premotor domains, in comparison with the combined practice. The sensorimotor system can acquire motor modules in a separated or integrated manner. However, the system appears to require integrated practice to coordinate the adaptations with the skill learning and the networks involved in the integrated behavior. This integration seems to be related to the acquisition of anticipatory mechanism of control and with the decrement of feedback control.

Posture Control-Human-Inspired Approaches for Humanoid Robot Benchmarking: Conceptualizing Tests, Protocols and Analyses.

Posture control is indispensable for both humans and humanoid robots, which becomes especially evident when performing sensorimotor tasks such as moving on compliant terrain or interacting with the environment. Posture control is therefore targeted in recent proposals of robot benchmarking in order to advance their development. This Methods article suggests corresponding robot tests of standing balance, drawing inspirations from the human sensorimotor system and presenting examples from robot experiments. To account for a considerable technical and algorithmic diversity among robots, we focus in our tests on basic posture control mechanisms, which provide humans with an impressive postural versatility and robustness. Specifically, we focus on the mechanically challenging balancing of the whole body above the feet in the sagittal plane around the ankle joints in concert with the upper body balancing around the hip joints. The suggested tests target three key issues of human balancing, which appear equally relevant for humanoid bipeds: (1) four basic physical disturbances (support surface (SS) tilt and translation, field and contact forces) may affect the balancing in any given degree of freedom (DoF). Targeting these disturbances allows us to abstract from the manifold of possible behavioral tasks. (2) Posture control interacts in a conflict-free way with the control of voluntary movements for undisturbed movement execution, both with “reactive” balancing of external disturbances and “proactive” balancing of self-produced disturbances from the voluntary movements. Our proposals therefore target both types of disturbances and their superposition. (3) Relevant for both versatility and robustness of the control, linkages between the posture control mechanisms across DoFs provide their functional cooperation and coordination at will and on functional demands. The suggested tests therefore include ankle-hip coordination. Suggested benchmarking criteria build on the evoked sway magnitude, normalized to robot weight and Center of mass (COM) height, in relation to reference ranges that remain to be established. The references may include human likeness features. The proposed benchmarking concept may in principle also be applied to wearable robots, where a human user may command movements, but may not be aware of the additionally required postural control, which then needs to be implemented into the robot.

Cortical morphometric changes after spinal cord injury

Neuroimaging studies suggest that spinal cord injury (SCI) may lead to significant anatomical alterations in the human sensorimotor system. In particular, voxel-based morphometry (VBM) of cortical volume has revealed a significant gray and white matter atrophy bilaterally in the primary sensory cortex (S1). By contrast, some structural studies failed to detect changes in gray matter volume (GMV) in the primary motor cortex (M1) following SCI, whereas others have reported a substantial decrease of GMV also in M1. In addition to direct degeneration of the sensorimotor cortex, SCI can also lead to atrophy of the non-sensorimotor cortex, such as anterior cingulate cortex, insular cortex, middle frontal gyrus and supplementary motor area. These findings suggest that SCI can cause remote atrophy of brain gray matter in the salient network. Furthermore, pain-related remodelling may occur in SCI. In fact, structural changes in SCI are also related to the presence and degree of below-level pain.We performed a systematic review of the neuroimaging studies showing morphometric cortical changes and subsequent functional reorganization in humans with SCI. Literature search was conducted using PubMed and Embase. We identified 12 articles matching the inclusion criteria and 195 patients were included in these studies. The wide range of disease duration, rehabilitation training, drug intervention, and different research methodology, especially the identification of region of interest and the statistical approach to correct for multiple comparisons, may have contributed to some inconsistencies between the reviewed studies. Nevertheless, neuroimaging biomarkers can assess the extent of neural damage, elucidate the mechanisms of neural repair, and predict clinical outcome. A better understanding of the structural and functional changes that occur at cortical level following SCI may be useful in tracking potential treatment induced changes and identifying potential therapeutic targets, thus developing evidence-based rehabilitation therapies.

Cortical Contribution to Linear, Non-linear and Frequency Components of Motor Variability Control during Standing.

Motor variability is an inherent feature of all human movements and reflects the quality of functional task performance. Depending on the requirements of the motor task, the human sensory-motor system is thought to be able to flexibly govern the appropriate level of variability. However, it remains unclear which neurophysiological structures are responsible for the control of motor variability. In this study, we tested the contribution of cortical cognitive resources on the control of motor variability (in this case postural sway) using a dual-task paradigm and furthermore observed potential changes in control strategy by evaluating Ia-afferent integration (H-reflex). Twenty healthy subjects were instructed to stand relaxed on a force plate with eyes open and closed, as well as while trying to minimize sway magnitude and performing a “subtracting-sevens” cognitive task. In total 25 linear and non-linear parameters were used to evaluate postural sway, which were combined using a Principal Components procedure. Neurophysiological response of Ia-afferent reflex loop was quantified using the Hoffman reflex. In order to assess the contribution of the H-reflex on the sway outcome in the different standing conditions multiple mixed-model ANCOVAs were performed. The results suggest that subjects were unable to further minimize their sway, despite actively focusing to do so. The dual-task had a destabilizing effect on PS, which could partly (by 4%) be counter-balanced by increasing reliance on Ia-afferent information. The effect of the dual-task was larger than the protective mechanism of increasing Ia-afferent information. We, therefore, conclude that cortical structures, as compared to peripheral reflex loops, play a dominant role in the control of motor variability.

Robotic assembly solution by human-in-the-loop teaching method based on real-time stiffness modulation

We propose a novel human-in-the-loop approach for teaching robots how to solve assembly tasks in unpredictable and unstructured environments. In the proposed method the human sensorimotor system is integrated into the robot control loop though a teleoperation setup. The approach combines a 3-DoF end-effector force feedback with an interface for modulation of the robot end-effector stiffness. When operating in unpredictable and unstructured environments, modulation of limb impedance is essential in terms of successful task execution, stability and safety. We developed a novel hand-held stiffness control interface that is controlled by the motion of the human finger. A teaching approach was then used to achieve autonomous robot operation. In the experiments, we analysed and solved two part-assembly tasks: sliding a bolt fitting inside a groove and driving a self-tapping screw into a material of unknown properties. We experimentally compared the proposed method to complementary robot learning methods and analysed the potential benefits of direct stiffness modulation in the force-feedback teleoperation.

Biofeedback Signals for Robotic Rehabilitation: Assessment of Wrist Muscle Activation Patterns in Healthy Humans.

Electrophysiological recordings from human muscles can serve as control signals for robotic rehabilitation devices. Given that many diseases affecting the human sensorimotor system are associated with abnormal patterns of muscle activation, such biofeedback can optimize human-robot interaction and ultimately enhance motor recovery. To understand how mechanical constraints and forces imposed by a robot affect muscle synergies, we mapped the muscle activity of seven major arm muscles in healthy individuals performing goal-directed discrete wrist movements constrained by a wrist robot. We tested six movement directions and four force conditions typically experienced during robotic rehabilitation. We analyzed electromyographic (EMG) signals using a space-by-time decomposition and we identified a set of spatial and temporal modules that compactly described the EMG activity and were robust across subjects. For each trial, coefficients expressing the strength of each combination of modules and representing the underlying muscle recruitment, allowed for a highly reliable decoding of all experimental conditions. The decomposition provides compact representations of the observable muscle activation constrained by a robotic device. Results indicate that a low-dimensional control scheme incorporating EMG biofeedback could be an effective add-on for robotic rehabilitative protocols seeking to improve impaired motor function in humans.

Does the sensorimotor system minimize prediction error or select the most likely prediction during object lifting?

Using a novel experimental model of object lifting, we tested whether the sensorimotor system models the weight of objects by minimizing lifting errors or by selecting the statistically most likely weight. We found that the sensorimotor system minimizes the square of prediction errors for object lifting. This parallels the results of studies that investigated visually guided reaching, suggesting an overlap in the underlying mechanisms between tasks that involve different sensory systems.

Ownership Status Influences the Degree of Joint Facilitatory Behavior

When engaging in joint activities, humans tend to sacrifice some of their own sensorimotor comfort and efficiency to facilitate a partner’s performance. In the two experiments reported here, we investigated whether ownership—a socioculturally based nonphysical feature ascribed to objects—influenced facilitatory motor behavior in joint action. Participants passed mugs that differed in ownership status across a table to a partner. We found that participants oriented handles less toward their partners when passing their own mugs than when passing mugs owned by their partners (Experiment 1) and mugs owned by the experimenter (Experiment 2). These findings indicate that individuals plan and execute actions that assist their partners but do so to a smaller degree if it is the individuals’ own property that the partners intend to manipulate. We discuss these findings in terms of underlying variables associated with ownership and conclude that a self-other distinction can be found in the human sensorimotor system.

A neuromorphic model of motor overflow in focal hand dystonia due to correlated sensory input

Objective. Motor overflow is a common and frustrating symptom of dystonia, manifested as unintentional muscle contraction that occurs during an intended voluntary movement. Although it is suspected that motor overflow is due to cortical disorganization in some types of dystonia (e.g. focal hand dystonia), it remains elusive which mechanisms could initiate and, more importantly, perpetuate motor overflow. We hypothesize that distinct motor elements have low risk of motor overflow if their sensory inputs remain statistically independent. But when provided with correlated sensory inputs, pre-existing crosstalk among sensory projections will grow under spike-timing-dependent-plasticity (STDP) and eventually produce irreversible motor overflow. Approach. We emulated a simplified neuromuscular system comprising two anatomically distinct digital muscles innervated by two layers of spiking neurons with STDP. The synaptic connections between layers included crosstalk connections. The input neurons received either independent or correlated sensory drive during 4 days of continuous excitation. The emulation is critically enabled and accelerated by our neuromorphic hardware created in previous work. Main results. When driven by correlated sensory inputs, the crosstalk synapses gained weight and produced prominent motor overflow; the growth of crosstalk synapses resulted in enlarged sensory representation reflecting cortical reorganization. The overflow failed to recede when the inputs resumed their original uncorrelated statistics. In the control group, no motor overflow was observed. Significance. Although our model is a highly simplified and limited representation of the human sensorimotor system, it allows us to explain how correlated sensory input to anatomically distinct muscles is by itself sufficient to cause persistent and irreversible motor overflow. Further studies are needed to locate the source of correlation in sensory input.

Motor memory: Representation, learning and consolidation

Abstract An efficient representation of motor system is vital to robot control and its ability to learn new skills. While the increasing sensor accuracy and the speed of signal processing failed to bridge the gap between the performance of artificial and human sensorimotor systems, the motor memory architecture seems to remain neglected. Despite the advances in robot skill learning, the latter remains limited to predefined tasks and pre-specified embodiment. We propose a new motor memory architecture that enables information sharing between different skills, on-line learning and off-line memory consolidation. We develop an algorithm for learning and consolidation of motor memory and study the space complexity of the representation in the experiments with humanoid robot Nao. Finally, we propose the integration of motor memory with sensor data into a common sensorimotor memory.

Good Posture, Good Balance: Comparison of Bioinspired and Model-Based Approaches for Posture Control of Humanoid Robots

This article provides a theoretical and thorough experimental comparison of two distinct posture control approaches: 1) a fully model-based control approach and 2) a biologically inspired approach derived from human observations. While the robotic approach can easily be applied to balancing in three-dimensional (3-D) and multicontact (MC) situations, the biologically inspired balancer currently only works in two-dimensional situations but shows interesting robustness properties under time delays in the feedback loop. This is an important feature when considering the signal transmission and processing properties in the human sensorimotor system. Both controllers were evaluated in a series of experiments with a torque-controlled humanoid robot (TORO). This article concludes with some suggestions for the improvement of model-based balancing approaches in robotics.

2A1-B09 筋活動の能動性が知覚された力覚の大きさに及ぼす影響の調査

This paper investigates the effects of muscle activities on human perceived forces. It is known that the activeness of force generation effects on attenuation of the perceived force. To investigate the mechanism of this phenomenon, we measured and compared the muscle activities in force generation tasks, which requires reproducing the perceived force by adjusting the force against the thumb actively or passively. Experimental results well followed the attenuation tendency reported in the past literature. We determined that main related muscle to adjust the force generation in our experiment was the ulnar extensor muscle of wrist. This muscle tends to increase the activity corresponding to the increase of the applied force only in the acive condition. This result indicates a possible connection between the muscle activities and the perceived forces in the human sensorimotor system.

The "Verge-Weight" Illusion

Our expectations of how heavy an object will be allow us to use the appropriate level of force to lift an object without having to rely on sensory feedback. After lifting an object from the verge of a table edge, we noted an appreciable change in the perceived weight of the object from when it was lifted from the table's center. To assess this in the lab, in a between-subjects design we had right-handed participants lift objects with their right hand from either the center, left edge, or right edge of a table, or from a pedestal with the same surface area as the base of the objects. On each trial, participants lifted one of three identically shaped cubes of different mass and reported the perceived weight of the object by magnitude estimation. The results show that observers persistently perceive objects placed at the left or right verge of a table edge as weighing more than those placed at the center of the table or those lifted from a pedestal. Comparing grip force rate of change between the index and thumb revealed force being exerted faster for the digit facing toward the table edge (i.e., index finger for right table edge) but only on the first lifting trial. This unexpected 'verge–weight' illusion (VWI), which was found for all objects tested, persisted long after initial errors in grip force rate had been corrected. Our results suggest that the affordance objects have for falling when placed at the verge of a support surface is used by the human sensorimotor system to apply grip force in an initially protective manner. The persistence of the VMI over successive lifts suggests that the perceived weight of objects remains biased from visual heuristics of object stability. Meeting abstract presented at VSS 2014

Physical and neural entrainment to rhythm: human sensorimotor coordination across tasks and effector systems.

The human sensorimotor system can be readily entrained to environmental rhythms, through multiple sensory modalities. In this review, we provide an overview of theories of timekeeping that make this neuroentrainment possible. First, we present recent evidence that contests the assumptions made in classic timekeeper models. The role of state estimation, sensory feedback and movement parameters on the organization of sensorimotor timing are discussed in the context of recent experiments that examined simultaneous timing and force control. This discussion is extended to the study of coordinated multi-effector movements and how they may be entrained.