21,398 research outputs found
Quantifying the time course of visual object processing using ERPs: it's time to up the game
Hundreds of studies have investigated the early ERPs to faces and objects using scalp and intracranial recordings. The vast majority of these studies have used uncontrolled stimuli, inappropriate designs, peak measurements, poor figures, and poor inferential and descriptive group statistics. These problems, together with a tendency to discuss any effect p < 0.05 rather than to report effect sizes, have led to a research field very much qualitative in nature, despite its quantitative inspirations, and in which predictions do not go beyond condition A > condition B. Here we describe the main limitations of face and object ERP research and suggest alternative strategies to move forward. The problems plague intracranial and surface ERP studies, but also studies using more advanced techniques – e.g., source space analyses and measurements of network dynamics, as well as many behavioral, fMRI, TMS, and LFP studies. In essence, it is time to stop amassing binary results and start using single-trial analyses to build models of visual perception
Gravitational Lensing & Stellar Dynamics
Strong gravitational lensing and stellar dynamics provide two complementary
and orthogonal constraints on the density profiles of galaxies. Based on
spherically symmetric, scale-free, mass models, it is shown that the
combination of both techniques is powerful in breaking the mass-sheet and
mass-anisotropy degeneracies. Second, observational results are presented from
the Lenses Structure & Dynamics (LSD) Survey and the Sloan Lens ACS (SLACS)
Survey collaborations to illustrate this new methodology in constraining the
dark and stellar density profiles, and mass structure, of early-type galaxies
to redshifts of unity.Comment: 6 pages, 2 figures; Invited contribution in the Proceedings of XXIst
IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris,
4-9 July 2005), eds G. A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP
Sciences
Electric field representation of pulsar intensity spectra
Pulsar dynamic spectra exhibit high visibility fringes arising from
interference between scattered radio waves. These fringes may be random or
highly ordered patterns, depending on the nature of the scattering or
refraction. Here we consider the possibility of decomposing pulsar dynamic
spectra -- which are intensity measurements -- into their constituent scattered
waves, i.e. electric field components. We describe an iterative method of
achieving this decomposition and show how the algorithm performs on data from
the pulsar B0834+06. The match between model and observations is good, although
not formally acceptable as a representation of the data. Scattered wave
components derived in this way are immediately useful for qualitative insights
into the scattering geometry. With some further development this approach can
be put to a variety of uses, including: imaging the scattering and refracting
structures in the interstellar medium; interstellar interferometric imaging of
pulsars at very high angular resolution; and mitigating pulse arrival time
fluctuations due to interstellar scattering.Comment: 7 Pages, 2 Figures, revised version, accepted by MNRA
Quantifying the uncertainty of contour maps
Contour maps are widely used to display estimates of spatial fields. Instead
of showing the estimated field, a contour map only shows a fixed number of
contour lines for different levels. However, despite the ubiquitous use of
these maps, the uncertainty associated with them has been given a surprisingly
small amount of attention. We derive measures of the statistical uncertainty,
or quality, of contour maps, and use these to decide an appropriate number of
contour lines, that relates to the uncertainty in the estimated spatial field.
For practical use in geostatistics and medical imaging, computational methods
are constructed, that can be applied to Gaussian Markov random fields, and in
particular be used in combination with integrated nested Laplace approximations
for latent Gaussian models. The methods are demonstrated on simulated data and
an application to temperature estimation is presented
Need for objective task-based evaluation of AI-based segmentation methods for quantitative PET
Artificial intelligence (AI)-based methods are showing substantial promise in
segmenting oncologic positron emission tomography (PET) images. For clinical
translation of these methods, assessing their performance on clinically
relevant tasks is important. However, these methods are typically evaluated
using metrics that may not correlate with the task performance. One such widely
used metric is the Dice score, a figure of merit that measures the spatial
overlap between the estimated segmentation and a reference standard (e.g.,
manual segmentation). In this work, we investigated whether evaluating AI-based
segmentation methods using Dice scores yields a similar interpretation as
evaluation on the clinical tasks of quantifying metabolic tumor volume (MTV)
and total lesion glycolysis (TLG) of primary tumor from PET images of patients
with non-small cell lung cancer. The investigation was conducted via a
retrospective analysis with the ECOG-ACRIN 6668/RTOG 0235 multi-center clinical
trial data. Specifically, we evaluated different structures of a commonly used
AI-based segmentation method using both Dice scores and the accuracy in
quantifying MTV/TLG. Our results show that evaluation using Dice scores can
lead to findings that are inconsistent with evaluation using the task-based
figure of merit. Thus, our study motivates the need for objective task-based
evaluation of AI-based segmentation methods for quantitative PET
Is traumatic and non-traumatic neck pain associated with brain alterations? : a systematic review
Background: Chronic neck pain affects 50% - 85% of people who have experienced an acute episode. This transition and the persistence of chronic complaints are believed to be mediated by brain alterations among different central mechanisms.
Objectives: This study aimed to systematically review and critically appraise the current existing evidence regarding structural and functional brain alterations in patients with whiplash associated disorders (WAD) and idiopathic neck pain (INP). Additionally, associations between brain alterations and clinical symptoms reported in neck pain patients were evaluated.
Study Design: Systematic review.
Methods: The present systematic review was performed according to the PRISMA guidelines. PubMed, Web of Science, and Cochrane databases were searched. First, the obtained articles were screened based on title and abstract. Secondly, the screening was based on the full text. Risk of bias in included studies was investigated.
Results: Twelve studies met the inclusion criteria. Alterations in brain morphology and function, including perfusion, neurotransmission, and blood oxygenation level dependent-signal, were demonstrated in chronic neck pain patients. There is some to moderate evidence for both structural and functional brain alterations in patients with chronic neck pain. In contrast, no evidence for structural brain alterations in acute neck pain patients was found.
Limitations: Only 12 articles were included, which allows only cautious conclusions to be drawn.
Conclusion: Brain alterations were observed in both patients with chronic WAD and chronic INP. Furthermore, more evidence exists for brain alterations in chronic WAD, and different underlying mechanisms might be present in both pathologies. In addition, pain and disability were correlated with the observed brain alterations. Accordingly, morphological and functional brain alterations should be further investigated in patients with chronic WAD and chronic INP with newer and more sensitive techniques, and associative clinical measurements seem indispensable in future research
Recommended from our members
ToScA North America (6 – 8 June 2017, The University of Texas, Austin, TX) Program
ToScA North America will address key areas of science,
including Multi-modal Imaging, Geosciences, Forensics, Increasing Contrast,
Educational Outreach, Data, Materials Science and Medical and Biological
Science.University of Texas High-Resolution X-ray CT Facility (UTCT);
Jackson School of Geosciences, The University of Texas at Austin;
Natural History Museum (London);
Royal Microscopical Society (Oxford, UK)Geological Science
Quantifying Changes in the Spatial Structure of Trabecular Bone
We apply recently introduced measures of complexity for the structural
quantfication of distal tibial bone. For the first time, we are able to
investigate the temporal structural alteration of trabecular bone. Based on
four patients, we show how bone may alter due to temporal immobilisation
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