259 research outputs found
Cognitive control: componential or emergent?
The past twenty-five years have witnessed an increasing awareness of the importance of cognitive control in the regulation of complex behavior. It now sits alongside attention, memory, language and thinking as a distinct domain within cognitive psychology. At the same time it permeates each of these sibling domains. This paper reviews recent work on cognitive control in an attempt to provide a context for the fundamental question addressed within this Topic: is cognitive control to be understood as resulting from the interaction of multiple distinct control processes or are the phenomena of cognitive control emergent
Assessing Interaction Networks with Applications to Catastrophe Dynamics and Disaster Management
In this paper we present a versatile method for the investigation of
interaction networks and show how to use it to assess effects of indirect
interactions and feedback loops. The method allows to evaluate the impact of
optimization measures or failures on the system. Here, we will apply it to the
investigation of catastrophes, in particular to the temporal development of
disasters (catastrophe dynamics). The mathematical methods are related to the
master equation, which allows the application of well-known solution methods.
We will also indicate connections of disaster management with excitable media
and supply networks. This facilitates to study the effects of measures taken by
the emergency management or the local operation units. With a fictious, but
more or less realistic example of a spreading epidemic disease or a wave of
influenza, we illustrate how this method can, in principle, provide decision
support to the emergency management during such a disaster. Similar
considerations may help to assess measures to fight the SARS epidemics,
although immunization is presently not possible
Immune hierarchy among HIV-1 CD8+ T cell epitopes delivered by dendritic cells depends on MHC-I binding irrespective of mode of loading and immunization in HLA-A*0201 mice
Recent human immunodeficiency virus type 1 (HIV-1) vaccination strategies aim at targeting a broad range of cytotoxic T lymphocyte (CTL) epitopes from different HIV-1 proteins by immunization with multiple CTL epitopes simultaneously. However, this may establish an immune hierarchical response, where the immune system responds to only a small number of the epitopes administered. To evaluate the feasibility of such vaccine strategies, we used the human leukocyte antigen (HLA)-A*0201 transgenic (tg) HHD murine in vivo model and immunized with dendritic cells pulsed with seven HIV-1-derived HLA-A*0201 binding CTL epitopes. The seven peptides were simultaneously presented on the same dendritic cell (DC) or on separate DCs before immunization to one or different lymphoid compartments. Data from this study showed that the T-cell response, as measured by cytolytic activity and γ-interferon (IFN-γ)-producing CD8+ T cells, mainly focused on two of seven administered epitopes. The magnitude of individual T-cell responses induced by immunization with multiple peptides correlated with their individual immunogenicity that depended on major histocompatibility class I binding and was not influenced by mode of loading or mode of immunization. These findings may have implications for the design of vaccines based on DCs when using multiple epitopes simultaneously
Grasping Objects with Environmentally Induced Position Uncertainty
Due to noisy motor commands and imprecise and ambiguous sensory information, there is often substantial uncertainty about the relative location between our body and objects in the environment. Little is known about how well people manage and compensate for this uncertainty in purposive movement tasks like grasping. Grasping objects requires reach trajectories to generate object-fingers contacts that permit stable lifting. For objects with position uncertainty, some trajectories are more efficient than others in terms of the probability of producing stable grasps. We hypothesize that people attempt to generate efficient grasp trajectories that produce stable grasps at first contact without requiring post-contact adjustments. We tested this hypothesis by comparing human uncertainty compensation in grasping objects against optimal predictions. Participants grasped and lifted a cylindrical object with position uncertainty, introduced by moving the cylinder with a robotic arm over a sequence of 5 positions sampled from a strongly oriented 2D Gaussian distribution. Preceding each reach, vision of the object was removed for the remainder of the trial and the cylinder was moved one additional time. In accord with optimal predictions, we found that people compensate by aligning the approach direction with covariance angle to maintain grasp efficiency. This compensation results in higher probability to achieve stable grasps at first contact than non-compensation strategies in grasping objects with directional position uncertainty, and the results provide the first demonstration that humans compensate for uncertainty in a complex purposive task
Evolutionary games on graphs
Game theory is one of the key paradigms behind many scientific disciplines
from biology to behavioral sciences to economics. In its evolutionary form and
especially when the interacting agents are linked in a specific social network
the underlying solution concepts and methods are very similar to those applied
in non-equilibrium statistical physics. This review gives a tutorial-type
overview of the field for physicists. The first three sections introduce the
necessary background in classical and evolutionary game theory from the basic
definitions to the most important results. The fourth section surveys the
topological complications implied by non-mean-field-type social network
structures in general. The last three sections discuss in detail the dynamic
behavior of three prominent classes of models: the Prisoner's Dilemma, the
Rock-Scissors-Paper game, and Competing Associations. The major theme of the
review is in what sense and how the graph structure of interactions can modify
and enrich the picture of long term behavioral patterns emerging in
evolutionary games.Comment: Review, final version, 133 pages, 65 figure
Thermodynamic Computing
The hardware and software foundations laid in the first half of the 20th
Century enabled the computing technologies that have transformed the world, but
these foundations are now under siege. The current computing paradigm, which is
the foundation of much of the current standards of living that we now enjoy,
faces fundamental limitations that are evident from several perspectives. In
terms of hardware, devices have become so small that we are struggling to
eliminate the effects of thermodynamic fluctuations, which are unavoidable at
the nanometer scale. In terms of software, our ability to imagine and program
effective computational abstractions and implementations are clearly challenged
in complex domains. In terms of systems, currently five percent of the power
generated in the US is used to run computing systems - this astonishing figure
is neither ecologically sustainable nor economically scalable. Economically,
the cost of building next-generation semiconductor fabrication plants has
soared past $10 billion. All of these difficulties - device scaling, software
complexity, adaptability, energy consumption, and fabrication economics -
indicate that the current computing paradigm has matured and that continued
improvements along this path will be limited. If technological progress is to
continue and corresponding social and economic benefits are to continue to
accrue, computing must become much more capable, energy efficient, and
affordable. We propose that progress in computing can continue under a united,
physically grounded, computational paradigm centered on thermodynamics. Herein
we propose a research agenda to extend these thermodynamic foundations into
complex, non-equilibrium, self-organizing systems and apply them holistically
to future computing systems that will harness nature's innate computational
capacity. We call this type of computing "Thermodynamic Computing" or TC.Comment: A Computing Community Consortium (CCC) workshop report, 36 page
Spatial Bistability Generates hunchback Expression Sharpness in the Drosophila Embryo
During embryonic development, the positional information provided by concentration gradients of maternal factors directs pattern formation by providing spatially dependent cues for gene expression. In the fruit fly, Drosophila melanogaster, a classic example of this is the sharp on–off activation of the hunchback (hb) gene at midembryo, in response to local concentrations of the smooth anterior–posterior Bicoid (Bcd) gradient. The regulatory region for hb contains multiple binding sites for the Bcd protein as well as multiple binding sites for the Hb protein. Some previous studies have suggested that Bcd is sufficient for properly sharpened Hb expression, yet other evidence suggests a need for additional regulation. We experimentally quantified the dynamics of hb gene expression in flies that were wild-type, were mutant for hb self-regulation or Bcd binding, or contained an artificial promoter construct consisting of six Bcd and two Hb sites. In addition to these experiments, we developed a reaction–diffusion model of hb transcription, with Bcd cooperative binding and hb self-regulation, and used Zero Eigenvalue Analysis to look for multiple stationary states in the reaction network. Our model reproduces the hb developmental dynamics and correctly predicts the mutant patterns. Analysis of our model indicates that the Hb sharpness can be produced by spatial bistability, in which hb self-regulation produces two stable levels of expression. In the absence of self-regulation, the bistable behavior vanishes and Hb sharpness is disrupted. Bcd cooperative binding affects the position where bistability occurs but is not itself sufficient for a sharp Hb pattern. Our results show that the control of Hb sharpness and positioning, by hb self-regulation and Bcd cooperativity, respectively, are separate processes that can be altered independently. Our model, which matches the changes in Hb position and sharpness observed in different experiments, provides a theoretical framework for understanding the data and in particular indicates that spatial bistability can play a central role in threshold-dependent reading mechanisms of positional information
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