6,514 research outputs found
Predictive learning, prediction errors, and attention: evidence from event-related potentials and eye tracking
Prediction error (‘‘surprise’’) affects the rate of learning: We learn more rapidly about cues for which we initially make incorrect predictions than cues for which our initial predictions are correct. The current studies employ electrophysiological measures to reveal early attentional differentiation of events that differ in their previous involvement in errors of predictive judgment.
Error-related events attract more attention, as evidenced by features of event-related scalp potentials previously implicated in selective visual attention (selection negativity, augmented anterior N1). The earliest differences detected occurred around 120 msec after stimulus onset, and distributed source localization (LORETA)
indicated that the inferior temporal regions were one source of the earliest differences. In addition, stimuli associated with the production of prediction errors show higher dwell times in an eyetracking procedure. Our data support the view that early attentional processes play a role in human associative learning
Utterance Selection Model of Language Change
We present a mathematical formulation of a theory of language change. The
theory is evolutionary in nature and has close analogies with theories of
population genetics. The mathematical structure we construct similarly has
correspondences with the Fisher-Wright model of population genetics, but there
are significant differences. The continuous time formulation of the model is
expressed in terms of a Fokker-Planck equation. This equation is exactly
soluble in the case of a single speaker and can be investigated analytically in
the case of multiple speakers who communicate equally with all other speakers
and give their utterances equal weight. Whilst the stationary properties of
this system have much in common with the single-speaker case, time-dependent
properties are richer. In the particular case where linguistic forms can become
extinct, we find that the presence of many speakers causes a two-stage
relaxation, the first being a common marginal distribution that persists for a
long time as a consequence of ultimate extinction being due to rare
fluctuations.Comment: 21 pages, 17 figure
Management of trypanosomiasis and leishmaniasis
<p>Background: The current treatments for human African trypanosomiasis (HAT), Chagas disease and leishmaniasis (collectively referred to as the kinetoplastid diseases) are far from ideal but, for some, there has been significant recent progress. For HAT the only advances in treatment over the past two decades have been the introduction of an eflornithine/nifurtimox co-administration and a shorter regime of the old standard melarsoprol.</p>
<p>Sources of data: PubMed.</p>
<p>Areas of Agreement: There is a need for new safe, oral drugs for cost-effective treatment of patients and use in control programmes for all the trypanosomatid diseases.</p>
<p>Areas of controversy: Cutaneous leishmaniasis is not on the agenda and treatments are lagging behind.</p>
<p>Growing points: There are three compounds in development for the treatment of the CNS stage of HAT: fexinidazole, currently due to entry into phase II clinical studies, a benzoxaborole (SCYX-7158) in phase I trials and a diamidine derivative (CPD-0802), in advanced pre-clinical development. For Chagas disease, two anti-fungal triazoles are now in clinical trial. In addition, clinical studies with benznidazole, a drug previously recommended only for acute stage treatment, are close to completion to determine the effectiveness in the treatment of early chronic and indeterminate Chagas disease. For visceral leishmaniasis new formulations, therapeutic switching, in particular AmBisome, and the potential for combinations of established drugs have significantly improved the opportunities for the treatment in the Indian subcontinent, but not in East Africa.</p>
<p>Areas timely for developing research: Improved diagnostic tools are needed to support treatment, for test of cure in clinical trials and for monitoring/surveillance of populations in control programmes.</p>
The effect of fatigue on climbing fluidity and hand movements
In rock climbing, climbers use their arms to regulate their posture on the wall, which can lead to localised muscle fatigue. Evidence shows fatigue is the primary cause of falls, but little is known about how fatigue specifically affects climbing rhythm and hand movements. The present study examined climbing fluidity and hand movements on an indoor climbing wall before and after a specific fatiguing protocol. Seventeen climbers completed three repetitions of a challenging climbing route (21 on Ewbank scale) with different levels of localised arm fatigue. Climbers’ movements were tracked using 3D motion capture, and their hand actions assessed using notational analysis. Seventy markers were used to create 15 rigid body segments and the participants\u27 centre of mass. The global entropy index was calculated on the path of the participants\u27 centre of mass. Climbers fell more often when fatigued, but there were no significant differences in hip jerk or global entropy index when fatigued. No significant differences were found between the number of exploratory or performatory hand movements with different amounts of fatigue. The results suggest that localised arm fatigue affects a climber’s ability to prevent themselves from falling, but it does not specifically affect their fluidity
Comet 9P/Tempel 1: Interpretation with the Deep Impact Results
According to our common understandings, the original surface of a
short-period comet nucleus has been lost by sublimation processes during its
close approaches to the Sun. Sublimation results in the formation of a dust
mantle on the retreated surface and in chemical differentiation of ices over
tens or hundreds of meters below the mantle. In the course of NASA's Deep
Impact mission, optical and infrared imaging observations of the ejecta plume
were conducted by several researchers, but their interpretations of the data
came as a big surprise: (1) The nucleus of comet 9P/Tempel 1 is free of a dust
mantle, but maintains its pristine crust of submicron-sized carbonaceous
grains; (2) Primordial materials are accessible already at a depth of several
tens of cm with abundant silicate grains of submicrometer sizes. In this study,
we demonstrate that a standard model of cometary nuclei explains well available
observational data: (1) A dust mantle with a thickness of ~1-2 m builds up on
the surface, where compact aggregates larger than tens of micrometers dominate;
(2) Large fluffy aggregates are embedded in chemically differentiated layers as
well as in the deepest part of the nucleus with primordial materials. We
conclude that the Deep Impact results do not need any peculiar view of a comet
nucleus.Comment: 11 pages, 1 figure, 1 table. ApJ letters, 673, L199-20
Cosmological Limits on the Neutrino Mass from the Lya Forest
The Lya forest in quasar spectra probes scales where massive neutrinos can
strongly suppress the growth of mass fluctuations. Using hydrodynamic
simulations with massive neutrinos, we successfully test techniques developed
to measure the mass power spectrum from the forest. A recent observational
measurement in conjunction with a conservative implementation of other
cosmological constraints places upper limits on the neutrino mass: m_nu < 5.5
eV for all values of Omega_m, and m_nu < 2.4 (Omega_m/0.17 -1) eV, if 0.2 <
Omega_m <0.5 as currently observationally favored (both 95 % C.L.).Comment: 4 pages, 2 ps figures, REVTex, submitted to Phys. Rev. Let
Galaxy Cluster Correlation Function to z ~ 1.5 in the IRAC Shallow Cluster Survey
We present the galaxy cluster autocorrelation function of 277 galaxy cluster
candidates with 0.25 \le z \le 1.5 in a 7 deg^2 area of the IRAC Shallow
Cluster Survey. We find strong clustering throughout our galaxy cluster sample,
as expected for these massive structures. Specifically, at = 0.5 we find a
correlation length of r_0 = 17.40^{+3.98}_{-3.10} h^-1 Mpc, in excellent
agreement with the Las Campanas Distant Cluster Survey, the only other
non-local measurement. At higher redshift, = 1, we find that strong
clustering persists, with a correlation length of r_0=19.14^{+5.65}_{-4.56}
h^-1 Mpc. A comparison with high resolution cosmological simulations indicates
these are clusters with halo masses of \sim 10^{14} Msun, a result supported by
estimates of dynamical mass for a subset of the sample. In a stable clustering
picture, these clusters will evolve into massive (10^{15} Msun) clusters by the
present day.Comment: 4 pages, 4 figures, 1 table. ApJ Letters, in pres
Evolution of the Cluster Mass and Correlation Functions in LCDM Cosmology
The evolution of the cluster mass function and the cluster correlation
function from z = 0 to z = 3 are determined using 10^6 clusters obtained from
high-resolution simulations of the current best-fit LCDM cosmology (\Omega_m =
0.27, \sigma_8 = 0.84, h = 0.7). The results provide predictions for
comparisons with future observations of high redshift clusters. A comparison of
the predicted mass function of low redshift clusters with observations from
early Sloan Digital Sky Survey data, and the predicted abundance of massive
distant clusters with observational results, favor a slightly larger amplitude
of mass fluctuations (\sigma_8 = 0.9) and lower density parameter (\Omega_m =
0.2); these values are consistent within 1-\sigma with the current
observational and model uncertainties. The cluster correlation function
strength increases with redshift for a given mass limit; the clusters were more
strongly correlated in the past, due to their increasing bias with redshift -
the bias reaches b = 100 at z = 2 for M > 5 x 10^13 h^-1 M_sun. The
richness-dependent cluster correlation function, represented by the correlation
scale versus cluster mean separation relation, R0-d, is generally consistent
with observations. This relation can be approximated as R_0 = 1.7 d^0.6 h^-1
Mpc for d = 20 - 60 h^-1 Mpc. The R0-d relation exhibits surprisingly little
evolution with redshift for z < 2; this can provide a new test of the current
LCDM model when compared with future observations of high redshift clusters.Comment: 20 pages, 9 figures, accepted for publication in Ap
Bias, redshift space distortions and primordial nongaussianity of nonlinear transformations: application to Lyman alpha forest
On large scales a nonlinear transformation of matter density field can be
viewed as a biased tracer of the density field itself. A nonlinear
transformation also modifies the redshift space distortions in the same limit,
giving rise to a velocity bias. In models with primordial nongaussianity a
nonlinear transformation generates a scale dependent bias on large scales. We
derive analytic expressions for these for a general nonlinear transformation.
These biases can be expressed entirely in terms of the one point distribution
function (PDF) of the final field and the parameters of the transformation. Our
analysis allows one to devise nonlinear transformations with nearly arbitrary
bias properties, which can be used to increase the signal in the large scale
clustering limit. We apply the results to the ionizing equilibrium model of
Lyman-alpha forest, in which Lyman-alpha flux F is related to the density
perturbation delta via a nonlinear transformation. Velocity bias can be
expressed as an average over the Lyman-alpha flux PDF. At z=2.4 we predict the
velocity bias of -0.1, compared to the observed value of -0.13 +/- 0.03. Bias
and primordial nongaussianity bias depend on the parameters of the
transformation. Measurements of bias can thus be used to constrain these
parameters, and for reasonable values of the ionizing background intensity we
can match the predictions to observations. Matching to the observed values we
predict the ratio of primordial nongaussianity bias to bias to have the
opposite sign and lower magnitude than the corresponding values for the highly
biased galaxies, but this depends on the model parameters and can also vanish
or change the sign.Comment: 18 pages, 1 figur
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