580 research outputs found
Active inference, evidence accumulation, and the urn task
Deciding how much evidence to accumulate before making a decision is a problem we and other animals often face, but one that is not completely understood. This issue is particularly important because a tendency to sample less information (often known as reflection impulsivity) is a feature in several psychopathologies, such as psychosis. A formal understanding of information sampling may therefore clarify the computational anatomy of psychopathology. In this theoretical letter, we consider evidence accumulation in terms of active (Bayesian) inference using a generic model of Markov decision processes. Here, agents are equipped with beliefs about their own behavior--in this case, that they will make informed decisions. Normative decision making is then modeled using variational Bayes to minimize surprise about choice outcomes. Under this scheme, different facets of belief updating map naturally onto the functional anatomy of the brain (at least at a heuristic level). Of particular interest is the key role played by the expected precision of beliefs about control, which we have previously suggested may be encoded by dopaminergic neurons in the midbrain. We show that manipulating expected precision strongly affects how much information an agent characteristically samples, and thus provides a possible link between impulsivity and dopaminergic dysfunction. Our study therefore represents a step toward understanding evidence accumulation in terms of neurobiologically plausible Bayesian inference and may cast light on why this process is disordered in psychopathology
Yes, they can! Three-banded armadillos Tolypeutes sp. (Cingulata: Dasypodidae) dig their own burrows.
It is believed that the two species of Tolypeutes Illiger, 1811are the only armadillos that do not dig their own burrows, and that these species simply re-use burrows dug by other species. Here, we show that Tolypeutes matacus (Desmarest, 1804) and Tolypeutes tricinctus (Linnaeus, 1758) dig their own burrows. We describe the burrows and three other types of shelters used by them, and provide measurements and frequency of use of the different types of shelter. We have studied free-ranging individuals of T. matacus in two locations in Central Brazil and individuals of T. tricinctus in semi-captivity in the Northeast of Brazil. Individuals of T. matacus were found primarily in small burrows (76%), straw nests (13%), shallow depressions covered with leaf-litter (7%) or in straw nests made on shallow depressions (4%). Adult males and females of T. matacus did not differ in frequency of use of different types of shelter. Sub-adults T. matacus used shallow depressions and nests more often (40%) than adults (22%) and nurslings (10%). Nurslings of T. matacus reused the shelters more frequently (66%), than sub-adults (46%) and adults (35%). Adult females reused burrows and other types of shelter more frequently than adult males. Tolypeutes tricinctus rested mainly in burrows and under leaf-litter, but did not dig depressions or build nests. Tolypeutes tricinctus occasionally used burrows dug by Euphractus sexcinctus (Linnaeus, 1758), but T. matacus never used burrows dug by other species. Nursling T. matacus always shared shelter with an adult female therefore, both used shelters with similar frequency. Adult females and nurslings of T. matacus reused shelters in higher frequency. That can be explained by the fact that adult females with offspring tend to remain for consecutive nights in the same burrow when cubs are recently born. Due to their smaller body size, subadult T. matacus used shelter strategies that require less energetic effort more frequently than adults and nurslings. The habit of covering the burrow entrance with foliage and the burrow?s reduced depth, indicates that Tolypeutes use of burrows is more likely to be related to parental care behavior and thermoregulation strategies than to defense mechanisms. We are confident that the burrows used for resting were indeed dug by Tolypeutes because, besides the direct observation of armadillos digging burrows, the measures of the burrows are very distinctive from those presented as characteristic for the co-occurring burrowing species and are congruent with Tolypeutes size and carapace shape. The newly acquired knowledge that species of Tolypeutes dig burrows can be used to increase the well-being of individuals kept in captivity by adapting enclosures to enable their digging behavior. In addition, this information contributes not only to the study of the ecology and natural history of the species, but can shed new light on the study of the anatomy of specialized diggers. Tolypeutes spp. can comprise the least fossorial of all living armadillo species, but they can no longer be classified as non-diggers
Universal Parametric Correlations of Conductance Peaks in Quantum Dots
We compute the parametric correlation function of the conductance peaks in
chaotic and weakly disordered quantum dots in the Coulomb blockade regime and
demonstrate its universality upon an appropriate scaling of the parameter. For
a symmetric dot we show that this correlation function is affected by breaking
time-reversal symmetry but is independent of the details of the channels in the
external leads. We derive a new scaling which depends on the eigenfunctions
alone and can be extracted directly from the conductance peak heights. Our
results are in excellent agreement with model simulations of a disordered
quantum dot.Comment: 12 pages, RevTex, 2 Postscript figure
GAUBERT, JoĂ«l, La Science politique dâErnst Cassirer. Pour une refondation symbolique de la raison pratique contre le mythe politique contemporain
Interactions and Interference in Quantum Dots: Kinks in Coulomb Blockade Peak Positions
We investigate the spin of the ground state of a geometrically confined
many-electron system. For atoms, shell structure simplifies this problem-- the
spin is prescribed by the well-known Hund's rule. In contrast, quantum dots
provide a controllable setting for studying the interplay of quantum
interference and electron-electron interactions in general cases. In a generic
confining potential, the shell-structure argument suggests a singlet ground
state for an even number of electrons. The interaction among the electrons
produces, however, accidental occurrences of spin-triplet ground states, even
for weak interaction, a limit which we analyze explicitly. Variaton of an
external parameter causes sudden switching between these states and hence a
kink in the conductance. Experimental study of these kinks would yield the
exchange energy for the ``chaotic electron gas''.Comment: 4 pages, 2 ps figs included using epsf.sty. Revision: added important
reference and consequent text changes, other small correction
âI think I'm more free with them'âConflict, Negotiation and Change in Intergenerational Relations in African Families Living in Britain
While the family is increasingly being recognised as pivotal to migration, there remain too few studies examining how migration impacts on intergenerational relationships. Although traditional intergenerational gaps are intensified by migration, arguably there has been an over-emphasis on the divisions between âtraditionalâ parents and âmodernâ children at the expense of examining the ways in which both generations adapt. As Foner and Dreby [2011. âRelations Between the Generations in Immigrant Families.â Annual Review of Sociology 37: 545â564] stress, the reality of post-migration intergenerational relations is inevitably more complex, requiring the examination of both conflict and cooperation. This article contributes to this growing literature by discussing British data from comparative projects on intergenerational relations in African families (in Britain, France and South Africa). It argues that particular understandings can be gained from examining the adaptation of parents and parenting strategies post-migration and how the reconfiguration of family relations can contribute to settlement. By focusing on how both parent and child generations engage in conflict and negotiation to redefine their relationships and expectations, it offers insight into how families navigate and integrate the values of two cultures. In doing so, it argues that the reconfiguration of gender roles as a result of migration offers families the space to renegotiate their relationships and make choices about what they transmit to the next generation
Universal Correlations of Coulomb Blockade Conductance Peaks and the Rotation Scaling in Quantum Dots
We show that the parametric correlations of the conductance peak amplitudes
of a chaotic or weakly disordered quantum dot in the Coulomb blockade regime
become universal upon an appropriate scaling of the parameter. We compute the
universal forms of this correlator for both cases of conserved and broken time
reversal symmetry. For a symmetric dot the correlator is independent of the
details in each lead such as the number of channels and their correlation. We
derive a new scaling, which we call the rotation scaling, that can be computed
directly from the dot's eigenfunction rotation rate or alternatively from the
conductance peak heights, and therefore does not require knowledge of the
spectrum of the dot. The relation of the rotation scaling to the level velocity
scaling is discussed. The exact analytic form of the conductance peak
correlator is derived at short distances. We also calculate the universal
distributions of the average level width velocity for various values of the
scaled parameter. The universality is illustrated in an Anderson model of a
disordered dot.Comment: 35 pages, RevTex, 6 Postscript figure
Finite temperature effects in Coulomb blockade quantum dots and signatures of spectral scrambling
The conductance in Coulomb blockade quantum dots exhibits sharp peaks whose
spacings fluctuate with the number of electrons. We derive the
temperature-dependence of these fluctuations in the statistical regime and
compare with recent experimental results. The scrambling due to Coulomb
interactions of the single-particle spectrum with the addition of an electron
to the dot is shown to affect the temperature-dependence of the peak spacing
fluctuations. Spectral scrambling also leads to saturation in the temperature
dependence of the peak-to-peak correlator, in agreement with recent
experimental results. The signatures of scrambling are derived using discrete
Gaussian processes, which generalize the Gaussian ensembles of random matrices
to systems that depend on a discrete parameter -- in this case, the number of
electrons in the dot.Comment: 14 pages, 4 eps figures included, RevTe
Joint modelling of multiple network wiews
Latent space models (LSM) for network data were introduced by Hoff et al. (2002) under the basic assumption that each node of the network has an unknown position in a D-dimensional Euclidean latent space: generally the smaller the distance between two nodes in the latent space, the greater their probability of being connected. In this paper we propose a variational inference approach to estimate the intractable posterior of the LSM. In many cases, different network views on the same set of nodes are available. It can therefore be useful to build a model able to jointly summarise the information given by all the network views. For this purpose, we introduce the latent space joint model (LSJM) that merges the information given by multiple network views assuming that the probability of a node being connected with other nodes in each network view is explained by a unique latent variable. This model is demonstrated on the analysis of two datasets: an excerpt of 50 girls from 'Teenage Friends and Lifestyle Study' data at three time points and the Saccharomyces cerevisiae genetic and physical protein-protein interactions
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