41 research outputs found
Neurofunctional Correlates of Ethical, Food-Related Decision-Making
A grant from the One-University Open Access Fund at the University of Kansas was used to defray the authorâs publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.For consumers today, the perceived ethicality of a foodâs production method can be as important a purchasing consideration as its price. Still, few studies have examined how, neurofunctionally, consumers are making ethical, food-related decisions. We examined how consumersâ ethical concern about a foodâs production method may relate to how, neurofunctionally, they make decisions whether to purchase that food. Forty-six participants completed a measure of the extent to which they took ethical concern into consideration when making food-related decisions. They then underwent a series of functional magnetic resonance imaging (fMRI) scans while performing a food-related decision-making (FRDM) task. During this task, they made 56 decisions whether to purchase a food based on either its price (i.e., high or low, the âprice conditionâ) or production method (i.e., with or without the use of cages, the âproduction method conditionâ), but not both. For 23 randomly selected participants, we performed an exploratory, whole-brain correlation between ethical concern and differential neurofunctional activity in the price and production method conditions. Ethical concern correlated negatively and significantly with differential neurofunctional activity in the left dorsolateral prefrontal cortex (dlPFC). For the remaining 23 participants, we performed a confirmatory, region-of-interest (ROI) correlation between the same variables, using an 8-mm3 volume situated in the left dlPFC. Again, the variables correlated negatively and significantly. This suggests, when making ethical, food-related decisions, the more consumers take ethical concern into consideration, the less they may rely on neurofunctional activity in the left dlPFC, possibly because making these decisions is more routine for them, and therefore a more perfunctory process requiring fewer cognitive resources
Branding and a childâs brain: an fMRI study of neural responses to logos
Branding and advertising have a powerful effect on both familiarity and preference for products, yet no neuroimaging studies have examined neural response to logos in children. Food advertising is particularly pervasive and effective in manipulating choices in children. The purpose of this study was to examine how healthy childrenâs brains respond to common food and other logos. A pilot validation study was first conducted with 32 children to select the most culturally familiar logos, and to match food and non-food logos on valence and intensity. A new sample of 17 healthy weight children were then scanned using functional magnetic resonance imaging. Food logos compared to baseline were associated with increased activation in orbitofrontal cortex and inferior prefrontal cortex. Compared to non-food logos, food logos elicited increased activation in posterior cingulate cortex. Results confirmed that food logos activate some brain regions in children known to be associated with motivation. This marks the first study in children to examine brain responses to culturally familiar logos. Considering the pervasiveness of advertising, research should further investigate how children respond at the neural level to marketing
The NANOGrav 15-year Data Set: Search for Anisotropy in the Gravitational-Wave Background
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav)
has reported evidence for the presence of an isotropic nanohertz gravitational
wave background (GWB) in its 15 yr dataset. However, if the GWB is produced by
a population of inspiraling supermassive black hole binary (SMBHB) systems,
then the background is predicted to be anisotropic, depending on the
distribution of these systems in the local Universe and the statistical
properties of the SMBHB population. In this work, we search for anisotropy in
the GWB using multiple methods and bases to describe the distribution of the
GWB power on the sky. We do not find significant evidence of anisotropy, and
place a Bayesian upper limit on the level of broadband anisotropy such
that . We also derive conservative estimates on the
anisotropy expected from a random distribution of SMBHB systems using
astrophysical simulations conditioned on the isotropic GWB inferred in the
15-yr dataset, and show that this dataset has sufficient sensitivity to probe a
large fraction of the predicted level of anisotropy. We end by highlighting the
opportunities and challenges in searching for anisotropy in pulsar timing array
data.Comment: 19 pages, 11 figures; submitted to Astrophysical Journal Letters as
part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave
Background. For questions or comments, please email [email protected]
The NANOGrav 15-Year Data Set: Detector Characterization and Noise Budget
Pulsar timing arrays (PTAs) are galactic-scale gravitational wave detectors.
Each individual arm, composed of a millisecond pulsar, a radio telescope, and a
kiloparsecs-long path, differs in its properties but, in aggregate, can be used
to extract low-frequency gravitational wave (GW) signals. We present a noise
and sensitivity analysis to accompany the NANOGrav 15-year data release and
associated papers, along with an in-depth introduction to PTA noise models. As
a first step in our analysis, we characterize each individual pulsar data set
with three types of white noise parameters and two red noise parameters. These
parameters, along with the timing model and, particularly, a piecewise-constant
model for the time-variable dispersion measure, determine the sensitivity curve
over the low-frequency GW band we are searching. We tabulate information for
all of the pulsars in this data release and present some representative
sensitivity curves. We then combine the individual pulsar sensitivities using a
signal-to-noise-ratio statistic to calculate the global sensitivity of the PTA
to a stochastic background of GWs, obtaining a minimum noise characteristic
strain of at 5 nHz. A power law-integrated analysis shows
rough agreement with the amplitudes recovered in NANOGrav's 15-year GW
background analysis. While our phenomenological noise model does not model all
known physical effects explicitly, it provides an accurate characterization of
the noise in the data while preserving sensitivity to multiple classes of GW
signals.Comment: 67 pages, 73 figures, 3 tables; published in Astrophysical Journal
Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational
Wave Background. For questions or comments, please email
[email protected]
The NANOGrav 15-year Data Set: Bayesian Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
Evidence for a low-frequency stochastic gravitational wave background has
recently been reported based on analyses of pulsar timing array data. The most
likely source of such a background is a population of supermassive black hole
binaries, the loudest of which may be individually detected in these datasets.
Here we present the search for individual supermassive black hole binaries in
the NANOGrav 15-year dataset. We introduce several new techniques, which
enhance the efficiency and modeling accuracy of the analysis. The search
uncovered weak evidence for two candidate signals, one with a
gravitational-wave frequency of 4 nHz, and another at 170 nHz. The
significance of the low-frequency candidate was greatly diminished when
Hellings-Downs correlations were included in the background model. The
high-frequency candidate was discounted due to the lack of a plausible host
galaxy, the unlikely astrophysical prior odds of finding such a source, and
since most of its support comes from a single pulsar with a commensurate binary
period. Finding no compelling evidence for signals from individual binary
systems, we place upper limits on the strain amplitude of gravitational waves
emitted by such systems.Comment: 23 pages, 13 figures, 2 tables. Accepted for publication in
Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set
and the Gravitational Wave Background. For questions or comments, please
email [email protected]
The NANOGrav 15-year data set: Search for Transverse Polarization Modes in the Gravitational-Wave Background
Recently we found compelling evidence for a gravitational wave background
with Hellings and Downs (HD) correlations in our 15-year data set. These
correlations describe gravitational waves as predicted by general relativity,
which has two transverse polarization modes. However, more general metric
theories of gravity can have additional polarization modes which produce
different interpulsar correlations. In this work we search the NANOGrav 15-year
data set for evidence of a gravitational wave background with quadrupolar
Hellings and Downs (HD) and Scalar Transverse (ST) correlations. We find that
HD correlations are the best fit to the data, and no significant evidence in
favor of ST correlations. While Bayes factors show strong evidence for a
correlated signal, the data does not strongly prefer either correlation
signature, with Bayes factors when comparing HD to ST correlations,
and for HD plus ST correlations to HD correlations alone. However,
when modeled alongside HD correlations, the amplitude and spectral index
posteriors for ST correlations are uninformative, with the HD process
accounting for the vast majority of the total signal. Using the optimal
statistic, a frequentist technique that focuses on the pulsar-pair
cross-correlations, we find median signal-to-noise-ratios of 5.0 for HD and 4.6
for ST correlations when fit for separately, and median signal-to-noise-ratios
of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While
the signal-to-noise-ratios for each of the correlations are comparable, the
estimated amplitude and spectral index for HD are a significantly better fit to
the total signal, in agreement with our Bayesian analysis.Comment: 11 pages, 5 figure
How to Detect an Astrophysical Nanohertz Gravitational-Wave Background
Analysis of pulsar timing data have provided evidence for a stochastic
gravitational wave background in the nHz frequency band. The most plausible
source of such a background is the superposition of signals from millions of
supermassive black hole binaries. The standard statistical techniques used to
search for such a background and assess its significance make several
simplifying assumptions, namely: i) Gaussianity; ii) isotropy; and most often
iii) a power-law spectrum. However, a stochastic background from a finite
collection of binaries does not exactly satisfy any of these assumptions. To
understand the effect of these assumptions, we test standard analysis
techniques on a large collection of realistic simulated datasets. The dataset
length, observing schedule, and noise levels were chosen to emulate the
NANOGrav 15-year dataset. Simulated signals from millions of binaries drawn
from models based on the Illustris cosmological hydrodynamical simulation were
added to the data. We find that the standard statistical methods perform
remarkably well on these simulated datasets, despite their fundamental
assumptions not being strictly met. They are able to achieve a confident
detection of the background. However, even for a fixed set of astrophysical
parameters, different realizations of the universe result in a large variance
in the significance and recovered parameters of the background. We also find
that the presence of loud individual binaries can bias the spectral recovery of
the background if we do not account for them.Comment: 14 pages, 8 figure
The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background
Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes, which produce different interpulsar correlations. In this work, we search the NANOGrav 15 yr data set for evidence of a gravitational-wave background with quadrupolar HD and scalar-transverse (ST) correlations. We find that HD correlations are the best fit to the data and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors âŒ2 when comparing HD to ST correlations, and âŒ1 for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis
The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars
We present observations and timing analyses of 68 millisecond pulsars (MSPs)
comprising the 15-year data set of the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA)
experiment that is sensitive to low-frequency gravitational waves. This is
NANOGrav's fifth public data release, including both "narrowband" and
"wideband" time-of-arrival (TOA) measurements and corresponding pulsar timing
models. We have added 21 MSPs and extended our timing baselines by three years,
now spanning nearly 16 years for some of our sources. The data were collected
using the Arecibo Observatory, the Green Bank Telescope, and the Very Large
Array between frequencies of 327 MHz and 3 GHz, with most sources observed
approximately monthly. A number of notable methodological and procedural
changes were made compared to our previous data sets. These improve the overall
quality of the TOA data set and are part of the transition to new pulsar timing
and PTA analysis software packages. For the first time, our data products are
accompanied by a full suite of software to reproduce data reduction, analysis,
and results. Our timing models include a variety of newly detected astrometric
and binary pulsar parameters, including several significant improvements to
pulsar mass constraints. We find that the time series of 23 pulsars contain
detectable levels of red noise, 10 of which are new measurements. In this data
set, we find evidence for a stochastic gravitational-wave background.Comment: 90 pages, 74 figures, 6 tables; published in Astrophysical Journal
Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational
Wave Background. For questions or comments, please email
[email protected]