405 research outputs found
Visual exploration pattern in hemineglect
The analysis of eye movement parameters in visual neglect such as cumulative fixation duration, saccade amplitude, or the numbers of saccades has been used to probe attention deficits in neglect patients, since the pattern of exploratory eye movements has been taken as a strong index of attention distribution. The current overview of the literature of visual neglect has its emphasis on studies dealing with eye movement and exploration analysis. We present our own results in 15 neglect patients. The free exploration behavior was analyzed in these patients presenting 32 naturalistic color photographs of everyday scenes. Cumulative fixation duration, spatial distribution of fixations in the horizontal and vertical plane, the number and amplitude of exploratory saccades was analyzed and compared with the results of an age-matched control group. A main result of our study was that in neglect patients, fixation distribution of free exploration of natural scenes is not only influenced by the left-right bias in the horizontal direction but also by the vertical directio
Street crossing behavior in younger and older pedestrians: an eye- and head-tracking study
Background Crossing a street can be a very difficult task for older pedestrians. With increased age and potential cognitive decline, older people take the decision to cross a street primarily based on vehiclesâ distance, and not on their speed. Furthermore, older pedestrians tend to overestimate their own walking speed, and could not adapt it according to the traffic conditions. Pedestriansâ behavior is often tested using virtual reality. Virtual reality presents the advantage of being safe, cost-effective, and allows using standardized test conditions. Methods This paper describes an observational study with older and younger adults. Street crossing behavior was investigated in 18 healthy, younger and 18 older subjects by using a virtual reality setting. The aim of the study was to measure behavioral data (such as eye and head movements) and to assess how the two age groups differ in terms of number of safe street crossings, virtual crashes, and missed street crossing opportunities. Street crossing behavior, eye and head movements, in older and younger subjects, were compared with non-parametric tests. Results The results showed that younger pedestrians behaved in a more secure manner while crossing a street, as compared to older people. The eye and head movements analysis revealed that older people looked more at the ground and less at the other side of the street to cross. Conclusions The less secure behavior in street crossing found in older pedestrians could be explained by their reduced cognitive and visual abilities, which, in turn, resulted in difficulties in the decision-making process, especially under time pressure. Decisions to cross a street are based on the distance of the oncoming cars, rather than their speed, for both groups. Older pedestrians look more at their feet, probably because of their need of more time to plan precise stepping movement and, in turn, pay less attention to the traffic. This might help to set up guidelines for improving senior pedestriansâ safety, in terms of speed limits, road design, and mixed physical-cognitive trainings
Effects of age and eccentricity on visual target detection
The aim of this study was to examine the effects of aging and target eccentricity on a visual search task comprising 30 images of everyday life projected into a hemisphere, realizing a ±90° visual field. The task performed binocularly allowed participants to freely move their eyes to scan images for an appearing target or distractor stimulus (presented at 10°; 30°, and 50° eccentricity). The distractor stimulus required no response, while the target stimulus required acknowledgment by pressing the response button. One hundred and seventeen healthy subjects (mean age = 49.63 years, SD = 17.40 years, age range 20â78 years) were studied. The results show that target detection performance decreases with age as well as with increasing eccentricity, especially for older subjects. Reaction time also increases with age and eccentricity, but in contrast to target detection, there is no interaction between age and eccentricity. Eye movement analysis showed that younger subjects exhibited a passive search strategy while older subjects exhibited an active search strategy probably as a compensation for their reduced peripheral detection performance
Precise mass-dependent QED contributions to leptonic g-2 at order alpha^2 and alpha^3
Improved values for the two- and three-loop mass-dependent QED contributions
to the anomalous magnetic moments of the electron, muon, and tau lepton are
presented. The Standard Model prediction for the electron (g-2) is compared
with its most precise recent measurement, providing a value of the
fine-structure constant in agreement with a recently published determination.
For the tau lepton, differences with previously published results are found and
discussed. An updated value of the fine-structure constant is presented in
"Note added after publication."Comment: 6 pages, 1 figure. v2: New determination of alpha presented (based on
the recent electron g-2 measurement). v3: New formulae added in Sec.IIB. v4:
Updated value of alpha presente
Deconstructing Non-Abelian Gauge Theories at One Loop
Deconstruction of 5D Yang-Mills gauge theories is studied in next-to-leading
order accuracy. We calculate one-loop corrections to the mass spectrum of the
non-linear gauged sigma-model, which is the low energy effective theory of the
deconstructed theory. Renormalization is carried out following the standard
procedure of effective field theories. The relation between the radius of the
compactified fifth dimension and the symmetry breaking scale of the non-linear
sigma-model is modified by radiative corrections. We demonstrate that one can
match the low lying spectrum of the gauge boson masses of the effective 4D
gauged non-linear sigma-model to the Kaluza-Klein modes of the 5D theory at
one-loop accuracy
Anomaly-matching and Higgs-less effective theories
We reconsider the low-energy effective theory for Higgs-less electroweak
symmetry breaking: we study the anomaly-matching in the situation where all
Goldstone fields disappear from the spectrum as a result of the Higgs
mechanism. We find that the global SU(2)_L x SU(2)_R x U(1)_{B-L} symmetry of
the underlying theory, which is spontaneously broken to SU(2)_{L+R} x
U(1)_{B-L} has to be anomaly-free. For the sake of generality, we include the
possibility of light spin-1/2 bound states resulting from the dynamics of the
strongly-interacting symmetry-breaking sector, in addition to the Goldstone
bosons. Such composite fermions may have non-standard couplings at the leading
order, and an arbitrary total B-L charge. In order to perform the
anomaly-matching in that case, we generalize the construction of the
Wess-Zumino effective lagrangian. Composite fermions beyond the three known
generations are theoretically allowed, and there are no restrictions from the
anomaly-matching on their couplings nor on their U(1)_{B-L} charge. Absence of
global anomalies for the composite sector as a whole does not preclude
anomalous triple gauge boson couplings arising from composite fermion
triangular diagrams. On the other hand, the trace of B-L over elementary
fermions must vanish if all Goldstone modes are to disappear from the spectrum.Comment: Keywords: Anomalies in Field and String Theories, Spontaneous
Symmetry Breaking, Beyond the Standard Model, Chiral Lagrangians. 33 pages, 7
figure
Hadronic light-by-light scattering contribution to the muon g-2
We review recent developments concerning the hadronic light-by-light
scattering contribution to the anomalous magnetic moment of the muon. We first
discuss why fully off-shell hadronic form factors should be used for the
evaluation of this contribution to the g-2. We then reevaluate the numerically
dominant pion-exchange contribution in the framework of large-N_C QCD, using an
off-shell pion-photon-photon form factor which fulfills all QCD short-distance
constraints, in particular, a new short-distance constraint on the off-shell
form factor at the external vertex in g-2, which relates the form factor to the
quark condensate magnetic susceptibility in QCD. Combined with available
evaluations of the other contributions to hadronic light-by-light scattering
this leads to the new result a_{\mu}(LbyL; had) = (116 \pm 40) x 10^{-11}, with
a conservative error estimate in view of the many still unsolved problems. Some
potential ways for further improvements are briefly discussed as well. For the
electron we obtain the new estimate a_{e}(LbyL; had) = (3.9 \pm 1.3) x
10^{-14}.Comment: 6 pages, 1 figure, to be published in the proceedings of the PhiPsi09
workshop, Oct. 13-16, 2009, Beijing, Chin
The electroweak chiral Lagrangian reanalyzed
In this paper we reanalyze the electroweak chiral Lagrangian with particular
focus on two issues related to gauge invariance. Our analysis is based on a
manifestly gauge-invariant approach that we introduced recently. It deals with
gauge-invariant Green's functions and provides a method to evaluate the
corresponding generating functional without fixing the gauge. First we show,
for the case where no fermions are included in the effective Lagrangian, that
the set of low-energy constants currently used in the literature is redundant.
In particular, by employing the equations of motion for the gauge fields one
can choose to remove two low-energy constants which contribute to the
self-energies of the gauge bosons. If fermions are included in the effective
field theory analysis the situation is more involved. Even in this case,
however, these contributions to the self-energies of the gauge bosons can be
removed. The relation of this result to the experimentally determined values
for the oblique parameters S, T, and U is discussed. In the second part of the
paper we consider the matching relation between a full and an effective theory.
We show how the low-energy constants of the effective Lagrangian can be
determined by matching gauge-invariant Green's functions in both theories. As
an application we explicitly evaluate the low-energy constants for the standard
model with a heavy Higgs boson. The matching at the one-loop level and at
next-to-leading order in the low-energy expansion is performed employing
functional methods.Comment: 44 pages, Revtex. v2: Sections II and III interchanged. New section
II now self-contained. Discussions improved in sections I, II, V.C and VI.
Conclusions unchanged. Published versio
Status of KLOE-2
In a few months the KLOE-2 detector is expected to start data taking at the
upgraded DANE -factory of INFN Laboratori Nazionali di
Frascati. It aims to collect 25 fb at the peak, and about 5
fb in the energy region between 1 and 2.5 GeV. We review the status and
physics program of the projectComment: 6 pages, 5 figures, to appear in the Proceedings of the PHIPSI09
Workshop, Oct 13-16, 2009, Beijing, Chin
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