This paper concerns how motor actions are neurally represented and coded. Action planning and motor preparation can be studied using a specific type of representational activity, motor imagery. A close functional equivalence between motor imagery and motor preparation is suggested by the positive effects of imagining movements on motor learning, the similarity between the neural structures involved, and the similar physiological correlates observed in both imaging and preparing. The content of motor representations can be inferred from motor images at a macroscopic level, based on global aspects of the action (the duration and amount of effort involved) and the motor rules and constraints which predict the spatial path and kinematics of movements. A more microscopic neural account calls for a representation of object-oriented action. Object attributes are processed in different neural pathways depending on the kind of task the subject is performing. During object-oriented action, a pragmatic representation is activated in which object affordances are transformed into specific motor schemas (independently of other tasks such as object recognition). Animal as well as human clinical data implicate the posterior parietal and premotor cortical areas in schema instantiation. A mechanism is proposed that is able to encode the desired goal of the action and is applicable to different levels of representational organization.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0140525X00034026

The representing brain: Neural correlates of motor intention and imagery

How might one account for the organization in behavior without attributing it to an internal control structure? The present article develops a theoretical framework called behavioral dynamics that integrates an information-based approach to perception with a dynamical systems approach to action. For a given task, the agent and its environment are treated as a pair of dynamical systems that are coupled mechanically and informationally. Their interactions give rise to the behavioral dynamics, a vector field with attractors that correspond to stable task solutions, repellers that correspond to avoided states, and bifurcations that correspond to behavioral transitions. The framework is used to develop theories of several tasks in which a human agent interacts with the physical environment, including bouncing a ball on a racquet, balancing an object, braking a vehicle, and guiding locomotion. Stable, adaptive behavior emerges from the dynamics of the interaction between a structured environment and an agent with simple control laws, under physical and informational constraints.

/pdf/the-dynamics-of-perception-and-action-2dmb5k4w09.pdf

The dynamics of perception and action.

Evidence for a dichotomy between the planning of an action and its on-line control in humans is reviewed. This evidence suggests that planning and control each serve a specialized purpose utilizing distinct visual representations. Evidence from behavioral studies suggests that planning is influenced by a large array of visual and cognitive information, whereas control is influenced solely by the spatial characteristics of the target, including such things as its size, shape, orientation, and so forth. Evidence from brain imaging and neuropsychology suggests that planning and control are subserved by separate visual centers in the posterior parietal lobes, each constituting part of a larger network for planning and control. Planning appears to rely on phylogenetically newer regions in the inferior parietal lobe, along with the frontal lobes and basal ganglia, whereas control appears to rely on older regions in the superior parietal lobe, along with the cerebellum.

https://pure.royalholloway.ac.uk/portal/services/downloadRegister/4739215/S0140525X04000020a.pdf

Separate visual representations in the planning and control of action

Interpretation of images and videos containing humans interacting with different objects is a daunting task. It involves understanding scene or event, analyzing human movements, recognizing manipulable objects, and observing the effect of the human movement on those objects. While each of these perceptual tasks can be conducted independently, recognition rate improves when interactions between them are considered. Motivated by psychological studies of human perception, we present a Bayesian approach which integrates various perceptual tasks involved in understanding human-object interactions. Previous approaches to object and action recognition rely on static shape or appearance feature matching and motion analysis, respectively. Our approach goes beyond these traditional approaches and applies spatial and functional constraints on each of the perceptual elements for coherent semantic interpretation. Such constraints allow us to recognize objects and actions when the appearances are not discriminative enough. We also demonstrate the use of such constraints in recognition of actions from static images without using any motion information.

Observing Human-Object Interactions: Using Spatial and Functional Compatibility for Recognition

This target article presents a critical survey of the scientific literature dealing with the speed/accuracy trade-offs in rapid-aimed movements. It highlights the numerous mathematical and theoretical interpretations that have been proposed in recent decades. Although the variety of points of view reflects the richness of the field and the high degree of interest that such basic phenomena attract in the understanding of human movements, it calls into question the ability of 'many models to explain the basic observations consistently reported in the field. This target article summarizes the kinematic theory of rapid human movements, proposed recently by R. Plamondon (1993b; 1993c; 1995a; 1995b), and analyzes its predictions in the context of speed/accuracy trade-offs. Data from human movement literature are reanalyzed and reinterpreted in the context of the new theory. It is shown that the various aspects of speed/accuracy trade- offs can be taken into account by considering the asymptotic behavior of a large number of coupled linear systems, from which a delta- lognormal law can be derived to describe the velocity profile of an end-effector driven by a neuromuscular synergy. This law not only describes velocity profiles almost perfectly, it also predicts the kinematic properties of simple rapid movements and provides a consistent framework for the analysis of different types of speed/accuracy trade-offs using a quadratic (or power) law that emerges from the model.

/pdf/speed-accuracy-trade-offs-in-target-directed-movements-54xzivkka1.pdf

Speed/accuracy trade-offs in target-directed movements.

AUSTKA< T The underlying pirn-esses in movement organization and control were studied by varying the conditions under which arm movements were made. The three-dimensional movement trajectories of the following conditions were contrasted: pointing to a target with the index linger versus grasping a disk the same size as the target, grasping a fragile object versus a soil resilient object, and grasping a disk either to throw into a large box or place into a light litting well. Results showed that the arm trajectories, as represented by the resultant velocity profile of the wrist, varied considerably in their shape with the main factor being when peak velocity was reached as a function of the total duration of the movement. It appeared that when task demands required greater precision, the main deceleration phase of the trajectory was increased in duration. These results do not support a movement production mechanism that has access to an abstract representation of a base velocity profile and that creates trajectories by a simple scaling procedure in the temporal domain. Rather, the results support a view of movement production as relatively specific to the past experience of the performer and the constraints of the task. Ix's processus a la base du controlc el de ('organisation du mouvement out etc etudies en variant les conditions sous lesquelles les mouvements du bras etaient executes. Les trajectoires de mouvemenl tridimcnsionncl des conditions suivantes etaient niises en contraste: pointer une cible avee l'index versus saisir un disque de la meme taille que la cible; saisir un objet fragile versus un object elastique. mou; ct, saisir un disque suit pour le lancer dans une grnnde boitc soit le placer dans un puits bien ajustc. Les resultats indiquent que les trajectoires du bras, lelles que represenlees par le prolil de velocite resultant du poignel, varicnt considerablement dans leur forme avec le facteur principal apparaissant au moment ou 1c pic de velocite etait atteinl en tant que function de la duiee tolale du mouvement. Lorsque la tache requiert line plus grande precision la phase de deceleration principale dc la trajecloire augmente en duree. Cos resultats n'appuient pas un mccanisme dc production du mouvemenl ayant acccs a line representation abslraitc d'un prolil dc velocite dc base et creant des trajectoires par un procedc d'echelonncment simple dans le domaine temporcl. Cos resultats supported! plulol I \"idee d'unc production de mouvement coiiunc relativement specilique ii lexperience passcc du …

S. Athenes

Papers

Constraints on human arm movement trajectories.