992 research outputs found
Cross-dimensional Weighting for Aggregated Deep Convolutional Features
We propose a simple and straightforward way of creating powerful image
representations via cross-dimensional weighting and aggregation of deep
convolutional neural network layer outputs. We first present a generalized
framework that encompasses a broad family of approaches and includes
cross-dimensional pooling and weighting steps. We then propose specific
non-parametric schemes for both spatial- and channel-wise weighting that boost
the effect of highly active spatial responses and at the same time regulate
burstiness effects. We experiment on different public datasets for image search
and show that our approach outperforms the current state-of-the-art for
approaches based on pre-trained networks. We also provide an easy-to-use, open
source implementation that reproduces our results.Comment: Accepted for publications at the 4th Workshop on Web-scale Vision and
Social Media (VSM), ECCV 201
Feature Selectivity of the Gamma-Band of the Local Field Potential in Primate Primary Visual Cortex
Extracellular voltage fluctuations (local field potentials, LFPs) reflecting neural mass action are ubiquitous across species and brain regions. Numerous studies have characterized the properties of LFP signals in the cortex to study sensory and motor computations as well as cognitive processes like attention, perception and memory. In addition, its extracranial counterpart – the electroencephalogram – is widely used in clinical applications. However, the link between LFP signals and the underlying activity of local populations of neurons remains largely elusive. Here, we review recent work elucidating the relationship between spiking activity of local neural populations and LFP signals. We focus on oscillations in the gamma-band (30–90 Hz) of the LFP in the primary visual cortex (V1) of the macaque that dominate during visual stimulation. Given that in area V1 much is known about the properties of single neurons and the cortical architecture, it provides an excellent opportunity to study the mechanisms underlying the generation of the LFP
Hereditarily Indecomposable Banach algebras of diagonal operators
We provide a characterization of the Banach spaces with a Schauder basis
which have the property that the dual space is
naturally isomorphic to the space of diagonal operators
with respect to . We also construct a Hereditarily
Indecomposable Banach space with a Schauder basis
such that is isometric to
with these Banach algebras being
Hereditarily Indecomposable. Finally, we show that every is of the form , where
is a compact operator.Comment: 35 pages, submitted for publication to Israel J. Mat
Strictly singular non-compact diagonal operators on HI spaces
We construct a Hereditarily Indecomposable Banach space \eqs_d with a
Schauder basis \seq{e}{n} on which there exist strictly singular non-compact
diagonal operators. Moreover, the space \mc{L}_{\diag}(\eqs_d) of diagonal
operators with respect to the basis \seq{e}{n} contains an isomorphic copy of
Saturated extensions, the attractors method and Hereditarily James Tree Space
In the present work we provide a variety of examples of HI Banach spaces
containing no reflexive subspace and we study the structure of their duals as
well as the spaces of their linear bounded operators. Our approach is based on
saturated extensions of ground sets and the method of attractors
Dust remobilization in fusion plasmas under steady state conditions
The first combined experimental and theoretical studies of dust
remobilization by plasma forces are reported. The main theoretical aspects of
remobilization in fusion devices under steady state conditions are analyzed. In
particular, the dominant role of adhesive forces is highlighted and generic
remobilization conditions - direct lift-up, sliding, rolling - are formulated.
A novel experimental technique is proposed, based on controlled adhesion of
dust grains on tungsten samples combined with detailed mapping of the dust
deposition profile prior and post plasma exposure. Proof-of-principle
experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are
presented. The versatile environment of the linear device Pilot-PSI allowed for
experiments with different magnetic field topologies and varying plasma
conditions that were complemented with camera observations.Comment: 16 pages, 11 figures, 3 table
Spike sorting for large, dense electrode arrays
Developments in microfabrication technology have enabled the production of neural electrode arrays with hundreds of closely spaced recording sites, and electrodes with thousands of sites are under development. These probes in principle allow the simultaneous recording of very large numbers of neurons. However, use of this technology requires the development of techniques for decoding the spike times of the recorded neurons from the raw data captured from the probes. Here we present a set of tools to solve this problem, implemented in a suite of practical, user-friendly, open-source software. We validate these methods on data from the cortex, hippocampus and thalamus of rat, mouse, macaque and marmoset, demonstrating error rates as low as 5%
Comparing the Feature Selectivity of the Gamma-Band of the Local Field Potential and the Underlying Spiking Activity in Primate Visual Cortex
The local field potential (LFP), comprised of low-frequency extra-cellular voltage fluctuations, has been used extensively to study the mechanisms of brain function. In particular, oscillations in the gamma-band (30–90 Hz) are ubiquitous in the cortex of many species during various cognitive processes. Surprisingly little is known about the underlying biophysical processes generating this signal. Here, we examine the relationship of the local field potential to the activity of localized populations of neurons by simultaneously recording spiking activity and LFP from the primary visual cortex (V1) of awake, behaving macaques. The spatial organization of orientation tuning and ocular dominance in this area provides an excellent opportunity to study this question, because orientation tuning is organized at a scale around one order of magnitude finer than the size of ocular dominance columns. While we find a surprisingly weak correlation between the preferred orientation of multi-unit activity and gamma-band LFP recorded on the same tetrode, there is a strong correlation between the ocular preferences of both signals. Given the spatial arrangement of orientation tuning and ocular dominance, this leads us to conclude that the gamma-band of the LFP seems to sample an area considerably larger than orientation columns. Rather, its spatial resolution lies at the scale of ocular dominance columns
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