1,920 research outputs found
Working memory and attention in choice.
We study the role of attention and working memory in choices where options are presented sequentially rather than simultaneously. We build a model where a costly attention effort is chosen, which can vary over time. Evidence is accumulated proportionally to this effort and the utility of the reward. Crucially, the evidence accumulated decays over time. Optimal attention allocation maximizes expected utility from final choice; the optimal solution takes the decay into account, so attention is preferentially devoted to later times; but convexity of the flow attention cost prevents it from being concentrated near the end. We test this model with a choice experiment where participants observe sequentially two options. In our data the option presented first is, everything else being equal, significantly less likely to be chosen. This recency effect has a natural explanation with appropriate parameter values in our model of leaky evidence accumulation, where the decline is stronger for the option observed first. Analysis of choice, response time and brain imaging data provide support for the model. Working memory plays an essential role. The recency bias is stronger for participants with weaker performance in working memory tasks. Also activity in parietal areas, coding the stored value in working, declines over time as predicted
Reflecting on nostalgic, positive, and novel experiences increases state Openness
Objective
Personality change is a growing field of interest, but relatively few studies have examined causes of change in Openness. We investigated whether it is possible to influence state Openness, and through what mechanisms this effect may occur.
Method
In two experiments (Study 1: N = 144, Mage = 36.4, 58% female, 88% White; Study 2: N = 269, Mage = 34.0, 60% female, 91% White), participants reflected on and wrote about a personal experience requested to be either: nostalgic; positive and novel (Study 1); positive or novel (Study 2); or ordinary. They rated the events for nostalgia, positivity, novelty, and sociality, and completed measures of state positive affect, selfâesteem, social connectedness, meaning in life, and state Openness.
Results
Participants who recalled positive and/or novel events reported greater state Openness than those who recalled ordinary events. In Study 1, this also applied to those recalling nostalgic events. Event ratings of positivity (both studies), nostalgia and novelty (Study 2) independently predicted state Openness. State positive affect and selfâesteem were independent predictors in both studies, suggesting possible indirect paths.
Conclusions
Reflecting on nostalgic, positive, and novel experiences can increase state Openness. This finding may be useful for interventions targeting traitâlevel change
Blunted cardiovascular responses to acute psychological stress predict low behavioral but not self-reported perseverance
Emerging evidence relates attenuated physiological stress reactions to poor behavioral regulation. However, only a small number of behaviors such as impulsivity and risk taking have been explored. Nevertheless, one opportunistic study suggested that blunted reactivity might relate to poor perseverance. The present study examined the relationship between cardiovascular reactivity to acute active psychological stress and selfâreported and behavioral perseverance. Participants (N = 64) completed a selfâreport perseverance questionnaire before heart rate (HR) and blood pressure (BP) were measured at rest and in response to 4âmin active (paced auditory serial addition; PASAT) and passive (cold pressor) stress tests. This was followed by an unsolvable Euler puzzle tracing task, with the time spent and number of attempts endeavoring to solve the puzzle recorded as behavioral perseverance measures. Blunted systolic and diastolic BP reactivity to the PASAT was associated with fewer attempts at the impossible puzzle, and lower diastolic BP PASAT reactivity related to less time persevering at the puzzle. Moreover, attenuated diastolic BP and HR PASAT reactivity predicted poorer perseverance at keeping one's hand in the iced water of the cold pressor task. There was no association between reactivity and selfâreported perseverance. These preliminary findings add to the evidence that implicates blunted reactivity as a physiological marker of poor behavioral regulation, and this may indicate why individuals with blunted reactivity are at increased risk of developing negative health outcomes (e.g., obesity and addictions)
Correlation functions and emission time sequence of light charged particles from projectile-like fragment source in E/A = 44 and 77 MeV 40Ar + 27Al collisions
Two-particle correlation functions, involving protons, deuterons, tritons,
and alpha-particles, have been measured at very forward angles (0.7 deg <
theta_lab < 7 deg), in order to study projectile-like fragment (PLF) emission
in E/A = 44 and 77 MeV 40Ar + 27Al collisions. Peaks, originating from
resonance decays, are larger at E/A = 44 than at 77 MeV. This reflects the
larger relative importance of independently emitted light particles, as
compared to two-particle decay from unstable fragments, at the higher beam
energy. The time sequence of the light charged particles, emitted from the PLF,
has been deduced from particle-velocity-gated correlation functions (discarding
the contribution from resonance decays). Alpha-particles are found to have an
average emission time shorter than protons but longer than tritons and
deuterons.Comment: 18 pages, 5 figures, submitted to Nuclear Physics
Determining the 7Li(n,gamma) cross section via Coulomb dissociation of 8Li
The applicability of Coulomb dissociation reactions to determine the cross
section for the inverse neutron capture reaction was explored using the
reaction 8Li(gamma,n)7Li. A 69.5 MeV/nucleon 8Li beam was incident on a Pb
target, and the outgoing neutron and 7Li nucleus were measured in coincidence.
The deduced (n,gamma) excitation function is consistent with data for the
direct capture reaction 7Li(n,gamma)8Li and with low-energy effective field
theory calculations.Comment: Accepted for publication in Phys. Rev.
First observation of Li ground state
The ground state of neutron-rich unbound Li was observed for the first
time in a one-proton removal reaction from Be at a beam energy of 53.6
MeV/u. The Li ground state was reconstructed from Li and two
neutrons giving a resonance energy of 120 keV. All events
involving single and double neutron interactions in the Modular Neutron Array
(MoNA) were analyzed, simulated, and fitted self-consistently. The three-body
(Li+) correlations within Jacobi coordinates showed strong
dineutron characteristics. The decay energy spectrum of the intermediate
Li system (Li+) was described with an s-wave scattering length
of greater than -4 fm, which is a smaller absolute value than reported in a
previous measurement.Comment: Accepted for publication in Phys. Rev. C as a Rapid Communicatio
Probing Transport Theories via Two-Proton Source Imaging
Imaging technique is applied to two-proton correlation functions to extract
quantitative information about the space-time properties of the emitting source
and about the fraction of protons that can be attributed to fast emission
mechanisms. These new analysis techniques resolve important ambiguities that
bedeviled prior comparisons between measured correlation functions and those
calculated by transport theory. Quantitative comparisons to transport theory
are presented here. The results of the present analysis differ from those
reported previously for the same reaction systems. The shape of the two-proton
emitting sources are strongly sensitive to the details about the in-medium
nucleon-nucleon cross sections and their density dependence.Comment: 23 pages, 11 figures. Figures are in GIF format. If you need
postscript format, please contact: [email protected]
The AMANDA Neutrino Telescope and the Indirect Search for Dark Matter
With an effective telescope area of order 10^4 m^2, a threshold of ~50 GeV
and a pointing accuracy of 2.5 degrees, the AMANDA detector represents the
first of a new generation of high energy neutrino telescopes, reaching a scale
envisaged over 25 years ago. We describe its performance, focussing on the
capability to detect halo dark matter particles via their annihilation into
neutrinos.Comment: Latex2.09, 16 pages, uses epsf.sty to place 15 postscript figures.
Talk presented at the 3rd International Symposium on Sources and Detection of
Dark Matter in the Universe (DM98), Santa Monica, California, Feb. 199
The Study of TeV Variability and Duty Cycle of Mrk 421 from 3 Years of Observations with the Milagro Observatory
TeV flaring activity with time scales as short as tens of minutes and an
orphan TeV flare have been observed from the blazar Markarian 421 (Mrk 421).
The TeV emission from Mrk 421 is believed to be produced by leptonic
synchrotron self-Compton (SSC) emission. In this scenario, correlations between
the X-ray and the TeV fluxes are expected, TeV orphan flares are hardly
explained and the activity (measured as duty cycle) of the source at TeV
energies is expected to be equal or less than that observed in X-rays if only
SSC is considered. To estimate the TeV duty cycle of Mrk 421 and to establish
limits on its variability at different time scales, we continuously observed
Mrk 421 with the Milagro observatory. Mrk 421 was detected by Milagro with a
statistical significance of 7.1 standard deviations between 2005 September 21
and 2008 March 15. The observed spectrum is consistent with previous
observations by VERITAS. We estimate the duty cycle of Mrk 421 for energies
above 1 TeV for different hypothesis of the baseline flux and for different
flare selections and we compare our results with the X-ray duty cycle estimated
by Resconi et al. 2009. The robustness of the results is discussed.Comment: 27 pages, 6 figures, ApJ accepte
Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41
The Cygnus region is a very bright and complex portion of the TeV sky, host
to unidentified sources and a diffuse excess with respect to conventional
cosmic-ray propagation models. Two of the brightest TeV sources, MGRO J2019+37
and MGRO J2031+41, are analyzed using Milagro data with a new technique, and
their emission is tested under two different spectral assumptions: a power law
and a power law with an exponential cutoff. The new analysis technique is based
on an energy estimator that uses the fraction of photomultiplier tubes in the
observatory that detect the extensive air shower. The photon spectrum is
measured in the range 1 to 200 TeV using the last 3 years of Milagro data
(2005-2008), with the detector in its final configuration. MGRO J2019+37 is
detected with a significance of 12.3 standard deviations (), and is
better fit by a power law with an exponential cutoff than by a simple power
law, with a probability % (F-test). The best-fitting parameters for the
power law with exponential cutoff model are a normalization at 10 TeV of
, a spectral
index of and a cutoff energy of TeV. MGRO
J2031+41 is detected with a significance of 7.3, with no evidence of a
cutoff. The best-fitting parameters for a power law are a normalization of
and a
spectral index of . The overall flux is subject to an
30% systematic uncertainty. The systematic uncertainty on the power law
indices is 0.1. A comparison with previous results from TeV J2032+4130,
MGRO J2031+41 and MGRO J2019+37 is also presented.Comment: 11 pages, 10 figure
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