Fitts' law is not continuous in reciprocal aiming

It takes longer to accomplish difficult tasks than easy ones. In the context of motor behaviour, Fitts'' famous law states that the time needed to successfully execute an aiming movement increases linearly with task difficulty. While Fitts'' explicit formulation has met criticism, the relation between task difficulty and movement time is invariantly portrayed as continuous. Here, we demonstrate that Fitts'' law is discontinuous in reciprocal aiming owing to a transition in operative motor control mechanisms with increasing task difficulty. In particular, rhythmic movements are implemented in easy tasks and discrete movements in difficult ones. How movement time increases with task difficulty differs in both movement types. It appears, therefore, that the human nervous system abruptly engages a different control mechanism when task difficulty increases.     

An interdisciplinary approach to measurement

This meeting had as its theme the importance of good communications between workers in different disciplines. Papers and demonstrations were presented on a range of topics as apparently unrelated as the intraocular pressure, the tension of nitrogen in blood, and the experimental production of mesothelial tumours. In his introduction Dr J C Gilson showed how these were some recent end-products of research into pneumoconiosis. The work of the Pneumoconiosis Research Unit was centred round the properties of airborne dust and the acute and long-term effects of its inhalation. Studies ranged from the immunological responses of coal workers to surveys of men in some of the world's major asbestos fields; the latter were selected on account of the exposure to dust differing from that of workers in the UK in being confined to a single type of fibre. One link between the different studies was the features of the chest radiographs. For rounded opacities these were now read using the ILO Classification which was largely developed at the Unit; Dr Gilson demonstrated a recent extension to include the irregular opacities which are associated with exposure to asbestos.     

Variation approach to the problem of isoenergetic regulation of movement

It was shown theoretically that trajectories of movements might be invariant to energy expenditure of the organism. In this instance control parameters are changed discontinuously, and force actions of muscles are characterized by potentials. The analysis of well-known experimental data, as well as special investigations of human walking and forearm rhythmic movements confirmed that the activity of the muscle and nervous systems was adapted to the isoenergetic control.     

An integrated approach to the characterization of cell movement.

BACKGROUND: Most phenomena in developmental biology involve or depend upon cell migration. This article describes a comprehensive framework for the characterization and analysis of trajectories defined by cell movement. The following two perspectives are considered: (a) the behavior of each individual cell and (b) interactions between neighboring pairs of cells. METHODS: The measurements considered for individual trajectories include the velocity magnitude and orientation, maximum spatial dispersion, displacement effectiveness, and displacement entropies. Interactions between two trajectories are characterized by comparing the respective velocities. RESULTS: The potential of the overall framework is illustrated using data of moving cells in different biological environments. The work shows that it is possible to use the new algorithm presented here to characterize cell motility. CONCLUSIONS: The features of the algorithm were successful in determining the motility changes under different experimental conditions.     

A nonlinear approach to tracking slow-time-scale changes in movement kinematics

Degenerative processes like repetitive strain injuries (RSIs) cause normal movement patterns to change slowly over time. Accurately tracking how these disease/injury processes evolve over time and predicting their future progression could allow early intervention and prevent further deterioration. However, these processes often cannot be measured directly and first-principles models of these processes and how they affect movement control are highly complex and difficult to derive analytically. This study was conducted to determine if algorithms developed to track damage accumulation in mechanical systems without requiring first-principles models or direct measurements of the damage itself could also track a similar "hidden" process in a biomechanical context. Five healthy adults walked on a motorized treadmill at their preferred speed, while the treadmill inclination angle was slowly increased from 0 degrees (level) to approximately +8 degrees . Sagittal plane kinematics for the left hip, knee, and ankle joints were computed. The treadmill inclination angle was independently recorded and defined the "damage" to be tracked. Scalar tracking metrics were computed from the lower extremity walking kinematics. These metrics exhibited strong cubic relationships with treadmill inclination (88.9%相似文献   

A neuroscientific approach to normative judgment in law and justice

Developments in cognitive neuroscience are providing new insights into the nature of normative judgment. Traditional views in such disciplines as philosophy, religion, law, psychology and economics have differed over the role and usefulness of intuition and emotion in judging blameworthiness. Cognitive psychology and neurobiology provide new tools and methods for studying questions of normative judgment. Recently, a consensus view has emerged, which recognizes important roles for emotion and intuition and which suggests that normative judgment is a distributed process in the brain. Testing this approach through lesion and scanning studies has linked a set of brain regions to such judgment, including the ventromedial prefrontal cortex, orbitofrontal cortex, posterior cingulate cortex and posterior superior temporal sulcus. Better models of emotion and intuition will help provide further clarification of the processes involved. The study of law and justice is less well developed. We advance a model of law in the brain which suggests that law can recruit a wider variety of sources of information and paths of processing than do the intuitive moral responses that have been studied so far. We propose specific hypotheses and lines of further research that could help test this approach.     

A phenomenological approach to modelling collective cell movement in 2D

There are two main approaches to unraveling the mechanisms involved in the regulation of collective cell movement. On the one hand, “in vitro” tests try to represent “in vivo” conditions. On the other hand, “in silico” tests aim to model this movement through the use of complex numerically implemented mathematical methods. This paper presents a simple cell-based mathematical model to represent the collective movement phenomena. This approach is used to better understand the different interactive forces which guide cell movement, focusing mainly on the role of the cell propulsion force with the substrate. Different applications are simulated for 2D cell cultures, wound healing, and collective cell movement in substrates with different degrees of stiffness. The model provides a plausible explanation of how cells work together in order to regulate their movement, showing the significant influence of the propulsive force exerted by the cell to the substrate on guiding the collective cell movement and its interplay with other cell forces.     

New approach to analysis of deviations from hyperbolic law in enzyme kinetics

An empirical equation that describes deviations from Michaelian kinetics is proposed. The equation allows the limiting values of the Michaelis constant at v/Vmax --> 0 and v/Vmax --> 1 to be estimated (v is the rate of the enzymatic reaction and Vmax is the limiting value of v at saturating concentrations of substrate). The applicability of the equation is demonstrated for kinetic data obtained for glutamate dehydrogenases from various sources (negative kinetic cooperativity for coenzyme) and for biosynthetic threonine deaminase from pea seedlings (sharper approaching the limiting value of the enzymatic reaction rate with increasing substrate concentration in comparison with the hyperbolic law). The negative cooperativity for the function of saturation of protein by ligand is also analyzed (data on binding of spin-labeled NAD, NADH, and NADPH by beef liver glutamate dehydrogenase and binding of cupric ions by BSA are used as examples).     

A novel approach to the measurement of surfactant parameters in arthropod digestive juices

In arthropods, the determination of two important parameters of digestive juices, i.e. the total surfactant concentration and the critical micelle concentration (CMC), is challenging due to small sample volumes and low surfactant concentrations. In this work, we report a successful implementation of potentiometric titrations using the surfactant ion-selective electrode (SISE) and the pyrene fluorescence method (PFM) for the determination of the total surfactant concentration and CMC in the digestive juice of terrestrial isopod crustaceans Porcellio scaber. Pooled digestive juice extracts of four (SISE) or two (PFM) animals were used per measurement run. In both cases, digestive juice extracts in 100 μL of deionized water were sufficient for one measurement run. The total surfactant concentration of P. scaber digestive juice was determined to be 9.2 ± 3.5 mM and the CMC was approximately 90 μM. Our work presents an important improvement towards easy CMC determination in small volume samples in comparison with the commonly used stalagmometric technique, where much larger sample volumes are usually needed. To date, the total surfactant concentration was not measured in the digestive juices of arthropods other than Homarus vulgaris, Astacus leptodactylus and Cancer pagurus, for which complex separation and analytical techniques were required. Our results obtained by SISE and PFM therefore present the first successful quantification of surfactants and their CMC in small volumes of arthropod digestive juice without prior separation or purification techniques.     

On the limitations of standard statistical modeling in biological systems: A full Bayesian approach for biology

One of the most important scientific challenges today is the quantitative and predictive understanding of biological function. Classical mathematical and computational approaches have been enormously successful in modeling inert matter, but they may be inadequate to address inherent features of biological systems. We address the conceptual and methodological obstacles that lie in the inverse problem in biological systems modeling. We introduce a full Bayesian approach (FBA), a theoretical framework to study biological function, in which probability distributions are conditional on biophysical information that physically resides in the biological system that is studied by the scientist.     

The problem of measurement indeterminacy in complex neurobiological movement systems

In the study of complex neurobiological movement systems, measurement indeterminacy has typically been overcome by imposing artificial modelling constraints to reduce the number of unknowns (e.g., reducing all muscle, bone and ligament forces crossing a joint to a single vector). However, this approach prevents human movement scientists from investigating more fully the role, functionality and ubiquity of coordinative structures or functional motor synergies. Advancements in measurement methods and analysis techniques are required if the contribution of individual component parts or degrees of freedom of these task-specific structural units is to be established, thereby effectively solving the indeterminacy problem by reducing the number of unknowns. A further benefit of establishing more of the unknowns is that human movement scientists will be able to gain greater insight into ubiquitous processes of physical self-organising that underpin the formation of coordinative structures and the confluence of organismic, environmental and task constraints that determine the exact morphology of these special-purpose devices.