103 research outputs found
Temporal expectations modulate face image repetition suppression of early stimulus evoked event-related potentials
Repeated exposure to a stimulus leads to reduced responses of stimulus-selective sensory neurons, an effect known as repetition suppression or stimulus-specific adaptation. Several influential models have been proposed to explain repetition suppression within hierarchically-organised sensory systems, with each specifying different mechanisms underlying repetition effects. We manipulated temporal expectations within a face repetition experiment to test a critical prediction of the predictive coding model of repetition suppression: that repetition effects will be larger following stimuli that appear at expected times compared to stimuli that appear at unexpected times. We recorded event-related potentials from 18 participants and mapped the spatiotemporal progression of repetition effects using mass univariate analyses. We then assessed whether the magnitudes of observed face image repetition effects were influenced by temporal expectations. In each trial participants saw an adapter face, followed by a 500âŻms or 1000âŻms interstimulus interval (ISI), and then a test face, which was the same or a different face identity to the adapter. Participants' expectations for whether the test face would appear after a 500âŻms ISI were cued by the sex of the adapter face. Our analyses revealed multiple repetition effects with distinct scalp topographies, extending until at least 800âŻms from stimulus onset. An early (158-203âŻms) repetition effect was larger for stimuli following surprising, rather than expected, 500âŻms ISI durations, contrary to the model predictions of the predictive coding model of repetition suppression. During this time window temporal expectation effects were larger for alternating, compared to repeated, test stimuli. Statistically significant temporal expectation by stimulus repetition interactions were not found for later (230-609âŻms) time windows. Our results provide further evidence that repetition suppression can reduce neural effects of expectation and surprise, indicating that there are multiple interactive mechanisms supporting sensory predictions within the visual hierarchy.Daniel Feuerriegel, Owen Churches, Scott Coussens, Hannah A.D. Keag
Star Formation History at the Centers of Lenticular Galaxies with Bars and Purely Exponential Outer Disks from SAURON Data
We have investigated the stellar population properties in the central regions
of a sample of lenticular galaxies with bars and single-exponential outer
stellar disks using the data from the SAURON integral-field spectrograph
retrieved from the open Isaac Newton Group Archive. We have detected chemically
decoupled compact stellar nuclei with a metallicity twice that of the stellar
population in the bulges in seven of the eight galaxies. A starburst is
currently going on at the center of the eighth galaxy and we have failed to
determine the stellar population properties from its spectrum. The mean stellar
ages in the chemically decoupled nuclei found range from 1 to 11 Gyr. The
scenarios for the origin of both decoupled nuclei and lenticular galaxies as a
whole are discussed.Comment: 10 pages, 4 figures, a slightly edited version of the paper published
by Astronomy Letters, v. 37, no.1, 201
A study on the natural history of scanning behaviour in patients with visual field defects after stroke
BACKGROUND: A visual field defect (VFD) is a common consequence of stroke with a detrimental effect upon the survivors' functional ability and quality of life. The identification of effective treatments for VFD is a key priority relating to life post-stroke. Understanding the natural evolution of scanning compensation over time may have important ramifications for the development of efficacious therapies. The study aims to unravel the natural history of visual scanning behaviour in patients with VFD. The assessment of scanning patterns in the acute to chronic stages of stroke will reveal who does and does not learn to compensate for vision loss. METHODS/DESIGN: Eye-tracking glasses are used to delineate eye movements in a cohort of 100 stroke patients immediately after stroke, and additionally at 6 and 12 months post-stroke. The longitudinal study will assess eye movements in static (sitting) and dynamic (walking) conditions. The primary outcome constitutes the change of lateral eye movements from the acute to chronic stages of stroke. Secondary outcomes include changes of lateral eye movements over time as a function of subgroup characteristics, such as side of VFD, stroke location, stroke severity and cognitive functioning. DISCUSSION: The longitudinal comparison of patients who do and do not learn compensatory scanning techniques may reveal important prognostic markers of natural recovery. Importantly, it may also help to determine the most effective treatment window for visual rehabilitation.Tobias Loetscher, Celia Chen, Sophie Wignall, Andreas Bulling, Sabrina Hoppe, Owen Churches, Nicole A Thomas, Michael E R Nicholls and Andrew Le
Pedagogical approaches for e-assessment with authentication and authorship verification in Higher Education
Checking the identity of students and authorship of their online submissions is a major concern in Higher Education due to the increasing amount of plagiarism and cheating using the Internet. The literature on the effects of e-authentication systems for teaching staff is very limited because it is a novel procedure for them. A considerable gap is to understand teaching staffâ views regarding the use of e-authentication instruments and how they impact trust in e-assessment. This mixed-method study examines the concerns and practices of 108 teaching staff who used the TeSLA - Adaptive Trust-based e-Assessment System in six countries: UK, Spain, Netherlands, Bulgaria, Finland and Turkey. The findings revealed some technological, organisational and pedagogical issues related to accessibility, security, privacy and e-assessment design and feedback. Recommendations are to provide: a FAQ and an audit report with results, to raise awareness about data security and privacy, to develop policies and guidelines about fraud detection and prevention, e-assessment best practices and course team support
Status of the GEO600 gravitational wave detector
The GEO600 laser interferometric gravitational wave detector is approaching the end of its commissioning phase which started in 1995.During a test run in January 2002 the detector was operated for 15 days in a power-recycled michelson configuration. The detector and environmental data which were acquired during this test run were used to test the data analysis code. This paper describes the subsystems of GEO600, the status of the detector by August 2002 and the plans towards the first science run
Searching for gravitational waves from known pulsars
We present upper limits on the amplitude of gravitational waves from 28
isolated pulsars using data from the second science run of LIGO. The results
are also expressed as a constraint on the pulsars' equatorial ellipticities. We
discuss a new way of presenting such ellipticity upper limits that takes
account of the uncertainties of the pulsar moment of inertia. We also extend
our previous method to search for known pulsars in binary systems, of which
there are about 80 in the sensitive frequency range of LIGO and GEO 600.Comment: Accepted by CQG for the proceeding of GWDAW9, 7 pages, 2 figure
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
change
Setting upper limits on the strength of periodic gravitational waves from PSR J1939+2134 using the first science data from the GEO 600 and LIGO detectors
Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar's gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar's equatorial ellipticity
First upper limits from LIGO on gravitational wave bursts
We report on a search for gravitational wave bursts using data from the first
science run of the LIGO detectors. Our search focuses on bursts with durations
ranging from 4 ms to 100 ms, and with significant power in the LIGO sensitivity
band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than
1.6 events per day at 90% confidence level. This result is interpreted in terms
of the detection efficiency for ad hoc waveforms (Gaussians and sine-Gaussians)
as a function of their root-sum-square strain h_{rss}; typical sensitivities
lie in the range h_{rss} ~ 10^{-19} - 10^{-17} strain/rtHz, depending on
waveform. We discuss improvements in the search method that will be applied to
future science data from LIGO and other gravitational wave detectors.Comment: 21 pages, 15 figures, accepted by Phys Rev D. Fixed a few small typos
and updated a few reference
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