1,492 research outputs found
Frontoparietal representations of task context support the flexible control of goal-directed cognition.
Cognitive control allows stimulus-response processing to be aligned with internal goals and is thus central to intelligent, purposeful behavior. Control is thought to depend in part on the active representation of task information in prefrontal cortex (PFC), which provides a source of contextual bias on perception, decision making, and action. In the present study, we investigated the organization, influences, and consequences of context representation as human subjects performed a cued sorting task that required them to flexibly judge the relationship between pairs of multivalent stimuli. Using a connectivity-based parcellation of PFC and multivariate decoding analyses, we determined that context is specifically and transiently represented in a region spanning the inferior frontal sulcus during context-dependent decision making. We also found strong evidence that decision context is represented within the intraparietal sulcus, an area previously shown to be functionally networked with the inferior frontal sulcus at rest and during task performance. Rule-guided allocation of attention to different stimulus dimensions produced discriminable patterns of activation in visual cortex, providing a signature of top-down bias over perception. Furthermore, demands on cognitive control arising from the task structure modulated context representation, which was found to be strongest after a shift in task rules. When context representation in frontoparietal areas increased in strength, as measured by the discriminability of high-dimensional activation patterns, the bias on attended stimulus features was enhanced. These results provide novel evidence that illuminates the mechanisms by which humans flexibly guide behavior in complex environments
Temperature scaling in a dense vibro-fluidised granular material
The leading order "temperature" of a dense two dimensional granular material
fluidised by external vibrations is determined. An asymptotic solution is
obtained where the particles are considered to be elastic in the leading
approximation. The velocity distribution is a Maxwell-Boltzmann distribution in
the leading approximation. The density profile is determined by solving the
momentum balance equation in the vertical direction, where the relation between
the pressure and density is provided by the virial equation of state. The
predictions of the present analysis show good agreement with simulation results
at higher densities where theories for a dilute vibrated granular material,
with the pressure-density relation provided by the ideal gas law, are in error.
The theory also predicts the scaling relations of the total dissipation in the
bed reported by McNamara and Luding (PRE v 58, p 813).Comment: ReVTeX (psfrag), 5 pages, 5 figures, Submitted to PR
The neurobiology of reference-dependent value computation
A key focus of current research in neuroeconomics concerns how the human brain computes value. Although, value has generally been viewed as an absolute measure (e.g., expected value, reward magnitude), much evidence suggests that value is more often computed with respect to a changing reference point, rather than in isolation. Here, we present the results of a study aimed to dissociate brain regions involved in reference-independent (i.e., “absolute”) value computations, from those involved in value computations relative to a reference point. During functional magnetic resonance imaging, subjects acted as buyers and sellers during a market exchange of lottery tickets. At a behavioral level, we demonstrate that subjects systematically accorded a higher value to objects they owned relative to those they did not, an effect that results from a shift in reference point (i.e., status quo bias or endowment effect). Our results show that activity
in orbitofrontal cortex and dorsal striatum track parameters such as the expected value of lottery tickets indicating the computation of reference-independent value. In contrast, activity in ventral striatum indexed the degree to which stated prices, at a within-subjects and between-subjects level, were distorted with respect to a reference point. The findings speak to the neurobiological underpinnings of reference dependency during real market value computations
Mullidae: Goatfishes
Body elongate arid somewhat compressed. Two long unbranched barbels on chin; mouth low on head, the lower jaw inferior, the gape slightly diagonal; dentition variable but teeth conical, either in villiform bands or in 1 or 2 rows, never as enlarged canines (except slightly enlarged in adult males of the Atlantic Pseudupeneus). Two well-separated dorsal fins, the first of 7 or 8 (usually 8) slender spines (first spine often very small), the second of 9 rays (first unbranched); anal fin with 1 spine and 6 rays; caudal fin deeply forked, with 13 branched rays. Scales finely cterioid; head and body completely scaled (except preorbital region of some Upeneus), the number of nearvertical scale rows from upper end of gill opening to base of caudal fin 27 to 3
A note on the free convection boundary layer on a vertical surface with prescribed heat flux at small Prandtl number
It is shown that for a particular case of the surface heat flux the equations for small Prandtl number have simple analytical solutions. These are presented and compared with numerical solutions of the general equations
Non-Gaussian velocity distributions in excited granular matter in the absence of clustering
The velocity distribution of spheres rolling on a slightly tilted rectangular
two dimensional surface is obtained by high speed imaging. The particles are
excited by periodic forcing of one of the side walls. Our data suggests that
strongly non-Gaussian velocity distributions can occur in dilute granular
materials even in the absence of significant density correlations or
clustering. When the surface on which the particles roll is tilted further to
introduce stronger gravitation, the collision frequency with the driving wall
increases and the velocity component distributions approach Gaussian
distributions of different widths.Comment: 4 pages, 5 figures. Additional information at
http://physics.clarku.edu/~akudrolli/nls.htm
LineWalker: Line Search for Black Box Derivative-Free Optimization and Surrogate Model Construction
This paper describes a simple, but effective sampling method for optimizing
and learning a discrete approximation (or surrogate) of a multi-dimensional
function along a one-dimensional line segment of interest. The method does not
rely on derivative information and the function to be learned can be a
computationally-expensive ``black box'' function that must be queried via
simulation or other means. It is assumed that the underlying function is
noise-free and smooth, although the algorithm can still be effective when the
underlying function is piecewise smooth. The method constructs a smooth
surrogate on a set of equally-spaced grid points by evaluating the true
function at a sparse set of judiciously chosen grid points. At each iteration,
the surrogate's non-tabu local minima and maxima are identified as candidates
for sampling. Tabu search constructs are also used to promote diversification.
If no non-tabu extrema are identified, a simple exploration step is taken by
sampling the midpoint of the largest unexplored interval. The algorithm
continues until a user-defined function evaluation limit is reached. Numerous
examples are shown to illustrate the algorithm's efficacy and superiority
relative to state-of-the-art methods, including Bayesian optimization and
NOMAD, on primarily nonconvex test functions.Comment: 58 pages, 7 main figures, 29 total figure
Resources of Ribbon Fish and Cat Fish off the South West Coast of lndia
The acoustic surveys and fishing experiments
conducted by the research vessels
RASTRELLIGER and SARDINELLA of the
Pelagic Fishery Project from Ratnagiri to
the Gulf of Mannar for the past four years
have considerably enhanced our knowledge
of the pelagic fishery resources, their
abundance and seasonal distribution and
possible methods of exploitation (Anonymous
1974, 1975 & 1976). The average
annual landings of ribbon fish and cat fish
for the past ten years with 78,000tonnes
form only 7.7% of the total marine fish
production in India
Transport coefficients for an inelastic gas around uniform shear flow: Linear stability analysis
The inelastic Boltzmann equation for a granular gas is applied to spatially
inhomogeneous states close to the uniform shear flow. A normal solution is
obtained via a Chapman-Enskog-like expansion around a local shear flow
distribution. The heat and momentum fluxes are determined to first order in the
deviations of the hydrodynamic field gradients from their values in the
reference state. The corresponding transport coefficients are determined from a
set of coupled linear integral equations which are approximately solved by
using a kinetic model of the Boltzmann equation. The main new ingredient in
this expansion is that the reference state (zeroth-order
approximation) retains all the hydrodynamic orders in the shear rate. In
addition, since the collisional cooling cannot be compensated locally for
viscous heating, the distribution depends on time through its
dependence on temperature. This means that in general, for a given degree of
inelasticity, the complete nonlinear dependence of the transport coefficients
on the shear rate requires the analysis of the {\em unsteady} hydrodynamic
behavior. To simplify the analysis, the steady state conditions have been
considered here in order to perform a linear stability analysis of the
hydrodynamic equations with respect to the uniform shear flow state. Conditions
for instabilities at long wavelengths are identified and discussed.Comment: 7 figures; previous stability analysis modifie
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