12,297 research outputs found
How informative are spatial CA3 representations established by the dentate gyrus?
In the mammalian hippocampus, the dentate gyrus (DG) is characterized by
sparse and powerful unidirectional projections to CA3 pyramidal cells, the
so-called mossy fibers. Mossy fiber synapses appear to duplicate, in terms of
the information they convey, what CA3 cells already receive from entorhinal
cortex layer II cells, which project both to the dentate gyrus and to CA3.
Computational models of episodic memory have hypothesized that the function of
the mossy fibers is to enforce a new, well separated pattern of activity onto
CA3 cells, to represent a new memory, prevailing over the interference produced
by the traces of older memories already stored on CA3 recurrent collateral
connections. Can this hypothesis apply also to spatial representations, as
described by recent neurophysiological recordings in rats? To address this
issue quantitatively, we estimate the amount of information DG can impart on a
new CA3 pattern of spatial activity, using both mathematical analysis and
computer simulations of a simplified model. We confirm that, also in the
spatial case, the observed sparse connectivity and level of activity are most
appropriate for driving memory storage and not to initiate retrieval.
Surprisingly, the model also indicates that even when DG codes just for space,
much of the information it passes on to CA3 acquires a non-spatial and episodic
character, akin to that of a random number generator. It is suggested that
further hippocampal processing is required to make full spatial use of DG
inputs.Comment: 19 pages, 11 figures, 1 table, submitte
Human Motion Capture Data Tailored Transform Coding
Human motion capture (mocap) is a widely used technique for digitalizing
human movements. With growing usage, compressing mocap data has received
increasing attention, since compact data size enables efficient storage and
transmission. Our analysis shows that mocap data have some unique
characteristics that distinguish themselves from images and videos. Therefore,
directly borrowing image or video compression techniques, such as discrete
cosine transform, does not work well. In this paper, we propose a novel
mocap-tailored transform coding algorithm that takes advantage of these
features. Our algorithm segments the input mocap sequences into clips, which
are represented in 2D matrices. Then it computes a set of data-dependent
orthogonal bases to transform the matrices to frequency domain, in which the
transform coefficients have significantly less dependency. Finally, the
compression is obtained by entropy coding of the quantized coefficients and the
bases. Our method has low computational cost and can be easily extended to
compress mocap databases. It also requires neither training nor complicated
parameter setting. Experimental results demonstrate that the proposed scheme
significantly outperforms state-of-the-art algorithms in terms of compression
performance and speed
TopSig: Topology Preserving Document Signatures
Performance comparisons between File Signatures and Inverted Files for text
retrieval have previously shown several significant shortcomings of file
signatures relative to inverted files. The inverted file approach underpins
most state-of-the-art search engine algorithms, such as Language and
Probabilistic models. It has been widely accepted that traditional file
signatures are inferior alternatives to inverted files. This paper describes
TopSig, a new approach to the construction of file signatures. Many advances in
semantic hashing and dimensionality reduction have been made in recent times,
but these were not so far linked to general purpose, signature file based,
search engines. This paper introduces a different signature file approach that
builds upon and extends these recent advances. We are able to demonstrate
significant improvements in the performance of signature file based indexing
and retrieval, performance that is comparable to that of state of the art
inverted file based systems, including Language models and BM25. These findings
suggest that file signatures offer a viable alternative to inverted files in
suitable settings and from the theoretical perspective it positions the file
signatures model in the class of Vector Space retrieval models.Comment: 12 pages, 8 figures, CIKM 201
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