448 research outputs found
Can the Error Detection Mechanism Benefit from Training the Working Memory? A Comparison between Dyslexics and Controls — An ERP Study
BACKGROUND:Based on the relationship between working memory and error detection, we investigated the capacity of adult dyslexic readers' working memory to change as a result of training, and the impact of training on the error detection mechanism. METHODOLOGY:27 dyslexics and 34 controls, all university students, participated in the study. ERP methodology and behavioral measures were employed prior to, immediately after, and 6 months after training. The CogniFit Personal Coach Program, which consists of 24 sessions of direct training of working memory skills, was used. FINDINGS:Both groups of readers gained from the training program but the dyslexic readers gained significantly more. In the dyslexic group, digit span increased from 9.84+/-3.15 to 10.79+/-3.03. Working memory training significantly increased the number of words per minute read correctly by 14.73%. Adult brain activity changed as a result of training, evidenced by an increase in both working memory capacity and the amplitude of the Error-related Negativity (ERN) component (24.71%). When ERN amplitudes increased, the percentage of errors on the Sternberg tests decreased. CONCLUSIONS:We suggest that by expanding the working memory capacity, larger units of information are retained in the system, enabling more effective error detection. The crucial functioning of the central-executive as a sub-component of the working memory is also discussed
Involvement of the right hemisphere in reading comprehension: a DTI study
The Simple View of reading emphasizes the critical role of two factors in normal reading skills: word recognition and reading comprehension. The current study aims to identify the anatomical support for aspects of reading performance that fall within these two components. Fractional anisotropy (FA) values were obtained from Diffusion Tensor images in twenty-one typical adolescents and young adults using the Tract Based Spatial Statistics (TBSS) method. We focused on the Arcuate Fasciculus (AF) and Inferior Longitudinal Fasciculus (ILF) as fiber tracts that connect regions already implicated in the distributed cortical network for reading. Our results demonstrate dissociation between word-level and narrative-level reading skills: the FA values for both left and right ILF were correlated with measures of word reading, while only the left ILF correlated with reading comprehension scores. FA in the AF, however, correlated only with reading comprehension scores, bilaterally. Correlations with the right AF were particularly robust, emphasizing the contribution of the right hemisphere, especially the frontal lobe, to reading comprehension performance on the particular passage comprehension test used in this study. The anatomical dissociation between these reading skills is supported by the Simple View theory and may shed light on why these two skills dissociate in those with reading disorders
The slowly rotating near extremal D1-D5 system as a `hot tube'
The geometry of the D1-D5 system with a small angular momentum j has a long
throat ending in a conical defect. We solve the scalar wave equation for low
energy quanta in this geometry. The quantum is found to reflect off the end of
the throat, and stay trapped in the throat for a long time. The length of the
throat for j=1/2 equals n_1n_5 R, the length of the effective string in the
CFT; we also find that at this distance the incident wave becomes nonlinear.
Filling the throat with several quanta gives a `hot tube' which has emission
properties similar to those of the near extremal black hole.Comment: 31 pages, Latex, typo corrected, reference adde
Exactly solvable charged dilaton gravity theories in two dimensions
We find exactly solvable dilaton gravity theories containing a U(1) gauge
field in two dimensional space-time. The classical general solutions for the
gravity sector (the metric plus the dilaton field) of the theories coupled to a
massless complex scalar field are obtained in terms of the stress-energy tensor
and the U(1) current of the scalar field. We discuss issues that arise when we
attempt to use these models for the study of the gravitational back-reaction.Comment: The introductory part is changed. a version to appear in Class.
Quant. Grav. 6 pages, RevTe
Black Holes and D-branes
D-branes have been used to describe many properties of extremal and near
extremal black holes. These lecture notes provide a short review of these
developments.Comment: 13 pages, 2 figure
Evolution of near extremal black holes
Near extreme black holes can lose their charge and decay by the emission of
massive BPS charged particles. We calculate the greybody factors for low energy
charged and neutral scalar emission from four and five dimensional near
extremal Reissner-Nordstrom black holes. We use the corresponding emission
rates to obtain ratios of the rates of loss of excess energy by charged and
neutral emission, which are moduli independent, depending only on the integral
charges and the horizon potentials. We consider scattering experiments, finding
that evolution towards a state in which the integral charges are equal is
favoured, but neutral emission will dominate the decay back to extremality
except when one charge is much greater than the others. The implications of our
results for the agreement between black hole and D-brane emission rates and for
the information loss puzzle are then discussed.Comment: 25 pages, RevTe
Phase Transitions Between Solitons and Black Holes in Asymptotically AdS/ Spaces
We employ a thermodynamic analysis to determine the phase structure of
Eguchi-Hanson solitons, Schwarzschild-AdS/ black holes and
thermal AdS/. The Euclidean actions are calculated by two equable
means: the first uses the Eguchi-Hanson soliton as the thermal background while
the second makes use of minimal boundary counterterms in the action necessary
to render individual actions finite. The Euclidean actions are then utilised to
determine the phase structure in arbitrary odd dimension; it is found that
there is a Hawking-Page phase transition and also a phase transition between
the black hole and soliton. There is found to be no smooth phase transition
governed by an order parameter between AdS/ and the soliton but
nevertheless AdS/ changes phase by tunneling to the lower energy
soliton configuration.Comment: 7 pages, 1 figur
Brane-world generalizations of the Einstein static universe
A static Friedmann brane in a 5-dimensional bulk (Randall-Sundrum type
scenario) can have a very different relation between the density, pressure,
curvature and cosmological constant than in the case of the general
relativistic Einstein static universe. In particular, static Friedmann branes
with zero cosmological constant and 3-curvature, but satisfying rho>0 and
rho+3p>0, are possible. Furthermore, we find static Friedmann branes in a bulk
that satisfies the Einstein equations but is not Schwarzschild-anti de Sitter
or its specializations. In the models with negative bulk cosmological constant,
a positive brane tension leads to negative density and 3-curvature.Comment: additional interpretation of new solutions; accepted by
Class.Quant.Gra
D-brane Approach to Black Hole Quantum Mechanics
Strominger and Vafa have used D-brane technology to identify and precisely
count the degenerate quantum states responsible for the entropy of certain
extremal, BPS-saturated black holes. Here we give a Type-II D-brane description
of a class of extremal {\it and} non-extremal five-dimensional
Reissner-Nordstr\"om solutions and identify a corresponding set of degenerate
D-brane configurations. We use this information to do a string theory
calculation of the entropy, radiation rate and ``Hawking'' temperature. The
results agree perfectly with standard Hawking results for the corresponding
nearly extremal Reissner-Nordstr\"om black holes. Although these calculations
suffer from open-string strong coupling problems, we give some reasons to
believe that they are nonetheless qualitatively reliable. In this optimistic
scenario there would be no ``information loss'' in black hole quantum
evolution.Comment: 18 pages, uses harvmac and psfig. The new version of the paper
corrects various errors, omissions and obscurities of the original
submission. The major error was an underestimate of the severity of the
strong coupling problem in the D-brane description of black holes with a
macroscopic event horizon. The new version has a more sober, but still
optimistic assessment of what aspects of black hole quantum mechanics are be
brought under control by D-branes. We thank several correspondents for
helpful criticism and advic
Supersymmetric completion of supersymmetric quantum mechanics
Via supersymmetry argument, we determine the effective action of the SU(2)
supersymmetric Yang-Mills quantum mechanics up to two constants, which results
from the full supersymmetric completion of the F^4 term. The effective action,
consisting of zero, two, four, six and eight fermion terms, agrees with the
known perturbative one-loop calculations from the type II string theory and the
matrix theory. Our derivation thus demonstrates its non-renormalization
properties, namely, the one-loop exactness of the aforementioned action and the
absence of the non-perturbative corrections. We briefly discuss generalizations
to other branes and the comparison to the DLCQ supergravity analysis. In
particular, our results show that the stringent constraints from the
supersymmetry are responsible for the agreement between the matrix theory and
supergravity with sixteen supercharges.Comment: 26 pages, LaTeX, no figure
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