3,203 research outputs found
Route repetition and route retracing: effects of cognitive aging
Retracing a recently traveled route is a frequent navigation task when learning novel routes or exploring unfamiliar environments. In the present study we utilized virtual environments technology to investigate age-related differences in repeating and retracing a learned route. In the training phase of the experiment participants were guided along a route consisting of multiple intersections each featuring one unique landmark. In the subsequent test phase, they were guided along short sections of the route and asked to indicate overall travel direction (repetition or retracing), the direction required to continue along the route, and the next landmark they would encounter. Results demonstrate age-related deficits in all three tasks. More specifically, in contrast to younger participants, the older participants had greater problems during route retracing than during route repetition. While route repetition can be solved with egocentric response or route strategies, successfully retracing a route requires allocentric processing. The age-related deficits in route retracing are discussed in the context of impaired allocentric processing and shift from allocentric to egocentric navigation strategies as a consequence of age-related hippocampal degeneration. - See more at: http://journal.frontiersin.org/Journal/10.3389/fnagi.2012.00007/abstract#sthash.xK4Htsfy.dpu
Computing Majority with Triple Queries
Consider a bin containing balls colored with two colors. In a -query,
balls are selected by a questioner and the oracle's reply is related
(depending on the computation model being considered) to the distribution of
colors of the balls in this -tuple; however, the oracle never reveals the
colors of the individual balls. Following a number of queries the questioner is
said to determine the majority color if it can output a ball of the majority
color if it exists, and can prove that there is no majority if it does not
exist. We investigate two computation models (depending on the type of replies
being allowed). We give algorithms to compute the minimum number of 3-queries
which are needed so that the questioner can determine the majority color and
provide tight and almost tight upper and lower bounds on the number of queries
needed in each case.Comment: 22 pages, 1 figure, conference version to appear in proceedings of
the 17th Annual International Computing and Combinatorics Conference (COCOON
2011
Maladaptive bias for extrahippocampal navigation strategies in aging humans.
Efficient spatial navigation requires not only accurate spatial knowledge but also the selection of appropriate strategies. Using a novel paradigm that allowed us to distinguish between beacon, associative cue, and place strategies, we investigated the effects of cognitive aging on the selection and adoption of navigation strategies in humans. Participants were required to rejoin a previously learned route encountered from an unfamiliar direction. Successful performance required the use of an allocentric place strategy, which was increasingly observed in young participants over six experimental sessions. In contrast, older participants, who were able to recall the route when approaching intersections from the same direction as during encoding, failed to use the correct place strategy when approaching intersections from novel directions. Instead, they continuously used a beacon strategy and showed no evidence of changing their behavior across the six sessions. Given that this bias was already apparent in the first experimental session, the inability to adopt the correct place strategy is not related to an inability to switch from a firmly established response strategy to an allocentric place strategy. Rather, and in line with previous research, age-related deficits in allocentric processing result in shifts in preferred navigation strategies and an overall bias for response strategies. The specific preference for a beacon strategy is discussed in the context of a possible dissociation between beacon-based and associative-cue-based response learning in the striatum, with the latter being more sensitive to age-related changes
Redundant variables and Granger causality
We discuss the use of multivariate Granger causality in presence of redundant
variables: the application of the standard analysis, in this case, leads to
under-estimation of causalities. Using the un-normalized version of the
causality index, we quantitatively develop the notions of redundancy and
synergy in the frame of causality and propose two approaches to group redundant
variables: (i) for a given target, the remaining variables are grouped so as to
maximize the total causality and (ii) the whole set of variables is partitioned
to maximize the sum of the causalities between subsets. We show the application
to a real neurological experiment, aiming to a deeper understanding of the
physiological basis of abnormal neuronal oscillations in the migraine brain.
The outcome by our approach reveals the change in the informational pattern due
to repetitive transcranial magnetic stimulations.Comment: 4 pages, 5 figures. Accepted for publication in Physical Review
Evidence for age-related deficits in object-location binding during place recognition.
Deciding whether a place is the same or different than places encountered previously is a common task in daily navigation which requires to develop knowledge about the locations of objects (object-location binding) and to recognize places from different perspectives. These abilities rely on hippocampal functioning which is susceptible to increasing age. Thus, the question of the present study is how they both together impact on place recognition in aging. Forty people aged 20-29, 44 aged 60-69, and 32 aged 70-79 were presented with places consisting of four different objects during the encoding phase. In the test phase, they were then presented with a second place and had to decide whether it was the same or different. Test places were presented from different perspectives (0°, 30°, 60°) and with different object conditions (same, a swap of two objects, a substitution with a novel object). The sensitivity for detecting changes (d') decreased from 20-29 to 60-69 and to 70-79 years old, and with increasing perspective shifts. Importantly, older adults were less sensitive to object swapping than to object substitution, while young participants did not show any difference. Overall, these results suggest specific age-related difficulties in object-location binding in the context of place recognition
Intensity Coding in Two-Dimensional Excitable Neural Networks
In the light of recent experimental findings that gap junctions are essential
for low level intensity detection in the sensory periphery, the
Greenberg-Hastings cellular automaton is employed to model the response of a
two-dimensional sensory network to external stimuli. We show that excitable
elements (sensory neurons) that have a small dynamical range are shown to give
rise to a collective large dynamical range. Therefore the network transfer
(gain) function (which is Hill or Stevens law-like) is an emergent property
generated from a pool of small dynamical range cells, providing a basis for a
"neural psychophysics". The growth of the dynamical range with the system size
is approximately logarithmic, suggesting a functional role for electrical
coupling. For a fixed number of neurons, the dynamical range displays a maximum
as a function of the refractory period, which suggests experimental tests for
the model. A biological application to ephaptic interactions in olfactory nerve
fascicles is proposed.Comment: 17 pages, 5 figure
Avaliação da linguagem na divulgação científica : estudo de caso: Laboratório Nacional de Luz Síncrotron e o Laboratório Sirius
Orientador: Prof. Dr. Fabiano YokaichiyaCoorientador: Dra. Margareth K.K.D FrancoTrabalho de Conclusão de Curso (Graduação) - Universidade Federal do Paraná, Setor de Ciências Exatas, Curso de Graduação em FísicaInclui referênciasResumo : A divulgação científica pode ter diversos objetivos, dentre eles: o educacional, o engajamento em uma causa cientifica e a prestação de contas para a população sobre o dinheiro investido em grandes projetos científicos. Para que essa divulgação da ciência seja eficaz, devemos entender os meios de comunicação que fazem essa divulgação, o contexto socioeconômico de quem recebe a divulgação científica e, além disso, a linguagem utilizada. A divulgação para fins educacionais deve entender a realidade do educando e os seus conhecimentos prévios sobre o assunto. Para isso, neste trabalho faremos um estudo de caso da linguagem da divulgação científica educacional utilizada pelos produtores de conteúdo da TV Cultura na década de 1990 no Brasil. Já a divulgação científica de engajamento será analisada através da linguagem utilizada na campanha de vacinação nas décadas de 1980/1990, que ajudou a erradicar a poliomielite no Brasil. Essas análises citadas anteriormente são a base para o estudo principal que envolve o ensino de física. Nesse estudo principal analisaremos como se deu a linguagem de divulgação científica na construção do Laboratório Nacional de Luz Síncrotron nas décadas de 1980/1990 e como essa mesma linguagem se deu na divulgação do novo Laboratório SiriusAbstract: Scientific dissemination can have several objectives. We can mention: education, engagement in a scientific cause and accountability to the population for the money invested in large scientific projects. For this dissemination of science to be effective, we must understand the media that make this dissemination, the socioeconomic context of those who receive the scientific dissemination and, in addition, the language used. Disclosure for educational purposes must understand the reality of the student and their prior knowledge on the subject. For this, in this work we will make a case study of the language of educational science communication used by TV Cultura content producers in the 1990s in Brazil. The scientific dissemination of engagement will be analyzed through the language used in the vaccination campaign in the 1980s/1990s, which helped to eradicate polio in Brazil. These analyzes cited above are the basis for the main study involving the teaching of physics. In this main study, we will analyze how the language of scientific dissemination took place in the construction of the National Synchrotron Light Laboratory in the 1980s/1990s and how this same language occurred in the dissemination of the new Sirius Laboratory
The tidal tails of NGC 2298
We present an implementation of the matched-filter technique to detect tidal
tails of globular clusters. The method was tested using SDSS data for the
globular cluster Palomar 5 revealing its well known tidal tails. We also ran a
simulation of a globular cluster with a tidal tail where we successfully
recover the tails for a cluster at the same position and with the same
characteristics of NGC 2298. Based on the simulation we estimate that the
matched-filter increases the contrast of the tail relative to the background of
stars by a factor of 2.5 for the case of NGC 2298. We also present the
photometry of the globular cluster NGC 2298 using the MOSAIC2 camera installed
on the CTIO 4m telescope. The photometry covers ~ 3deg2 reaching V ~ 23. A fit
of a King profile to the radial density profile of NGC 2298 shows that this
cluster has a tidal radius of 15.91' \pm 1.07' which is twice as in the
literature. The application of the matched-filter to NGC 2298 reveals several
extra-tidal structures, including a leading and trailing tail. We also find
that NGC 2298 has extra-tidal structures stretching towards and against the
Galactic disk, suggesting strong tidal interaction. Finally, we assess how the
matched-filter performs when applied to a globular cluster with and without
mass segregation taken into account. We find that disregarding the effects of
mass segregation may significantly reduce the detection limit of the
matched-filter.Comment: 11 pages, 9 figures, 1 table. Accepted for publication on MNRAS main
journa
Precise measurements of radio-frequency magnetic susceptibility in (anti)ferromagnetic materials
Dynamic magnetic susceptibility, , was studied in several intermetallic
materials exhibiting ferromagnetic, antiferromagnetic and metamagnetic
transitions. Precise measurements by using a 14 MHz tunnel diode oscillator
(TDO) allow detailed insight into the field and temperature dependence of
. In particular, local moment ferromagnets show a sharp peak in
near the Curie temperature, . The peak amplitude decreases and shifts to
higher temperatures with very small applied dc fields. Anisotropic measurements
of CeVSb show that this peak is present provided the magnetic easy axis is
aligned with the excitation field. In a striking contrast, small moment,
itinerant ferromagnets (i.e., ZrZn) show a broad maximum in that
responds differently to applied field. We believe that TDO measurements provide
a very sensitive way to distinguish between local and itinerant moment magnetic
orders. Local moment antiferromagnets do not show a peak at the N\'eel
temperature, , but only a sharp decrease of below due to the
loss of spin-disorder scattering changing the penetration depth of the ac
excitation field. Furthermore, we show that the TDO is capable of detecting
changes in spin order as well as metamagnetic transitions. Finally, critical
scaling of in the vicinity of is discussed in CeVSb and
CeAgSb
Identifying nonlinear wave interactions in plasmas using two-point measurements: a case study of Short Large Amplitude Magnetic Structures (SLAMS)
A framework is described for estimating Linear growth rates and spectral
energy transfers in turbulent wave-fields using two-point measurements. This
approach, which is based on Volterra series, is applied to dual satellite data
gathered in the vicinity of the Earth's bow shock, where Short Large Amplitude
Magnetic Structures (SLAMS) supposedly play a leading role. The analysis
attests the dynamic evolution of the SLAMS and reveals an energy cascade toward
high-frequency waves.Comment: 26 pages, 13 figure
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