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Cortext: A columnar model of bottom-up and top-down processing in the neocortex

NEURAL NETWORKS 2009年第8期22卷 1055-1070页

作者： Schrader, Sven Gewaltig, Marc-Oliver Koerner, Ursula Koerner, Edgar Honda Res Inst Europe GmbH D-63073 Offenbach Germany

Experimental data suggests that a first hypothesis about the content of a complex visual scene is available as early as 150 ms after stimulus presentation. Other evidence suggests that recognition in the visual cortex of mammals is a bidirectional, often top-down driven process. Here, we present a spiking neural network model that demonstrates how the cortex can use both strategies: Faced with a new stimulus, the cortex first tries to catch the gist of the scene. The gist is then fed back as global hypothesis to influence and redirect further bottom-up processing. We propose that these two modes of processing are carried out in different layers of the cortex. A cortical column may, thus, be primarily defined by the specific connectivity that links neurons in different layers into a functional circuit. Given an input, our model generates an initial hypothesis after only a few milliseconds. The first wave of action potentials traveling up the hierarchy activates representations of features and feature combinations. In most cases, the correct feature representation is activated strongest and precedes all other candidates with millisecond precision. Thus, our model codes the reliability of a response in the relative latency of spikes. In the subsequent refinement stage where high-level activity modulates lower stages, this activation dominance is propagated back, influencing its own afferent activity to establish a unique decision. Thus, top-down influence de-activates representations that have contributed to the initial hypothesis about the current stimulus, comparable to predictive coding. Features that do not match the top-down prediction trigger an error signal that can be the basis for learning new representations. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Ventral visual pathway Spike-latency code predictive coding Modulation Spiking neuron models

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Changing meaning causes coupling changes within higher levels of the cortical hierarchy

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2009年第28期106卷 11765-11770页

作者： Schofield, T. M. Iverson, P. Kiebel, S. J. Stephan, K. E. Kilner, J. M. Friston, K. J. Crinion, J. T. Price, C. J. Leff, A. P. UCL Wellcome Trust Ctr Neuroimaging London WC1N 3BG England UCL Div Psychol & Language Sci London WC1N 1PF England Max Planck Inst Human Cognit & Brain Sci D-04103 Leipzig Germany Univ Zurich Inst Empir Res Econ Lab Social & Neural Syst Res CH-8006 Zurich Switzerland

Processing of speech and nonspeech sounds occurs bilaterally within primary auditory cortex and surrounding regions of the superior temporal gyrus;however, the manner in which these regions interact during speech and nonspeech processing is not well understood. Here, we investigate the underlying neuronal architecture of the auditory system with magnetoencephalography and a mismatch paradigm. We used a spoken word as a repeating "standard'' and periodically introduced 3 "oddball'' stimuli that differed in the frequency spectrum of the word's vowel. The closest deviant was perceived as the same vowel as the standard, whereas the other 2 deviants were perceived as belonging to different vowel categories. The neuronal responses to these vowel stimuli were compared with responses elicited by perceptually matched tone stimuli under the same paradigm. For both speech and tones, deviant stimuli induced coupling changes within the same bilateral temporal lobe system. However, vowel oddball effects increased coupling within the left posterior superior temporal gyrus, whereas perceptually equivalent nonspeech oddball effects increased coupling within the right primary auditory cortex. Thus, we show a dissociation in neuronal interactions, occurring at both different hierarchal levels of the auditory system (superior temporal versus primary auditory cortex) and in different hemispheres (left versus right). This hierarchical specificity depends on whether auditory stimuli are embedded in a perceptual context (i.e., a word). Furthermore, our lateralization results suggest left hemisphere specificity for the processing of phonological stimuli, regardless of their elemental (i.e., spectrotemporal) characteristics.

关键词： dynamic causal modeling language magnetoencephalography mismatch negativity predictive coding

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The mismatch negativity: A review of underlying mechanisms

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CLINICAL NEUROPHYSIOLOGY 2009年第3期120卷 453-463页

作者： Garrido, Marta I. Kilner, James M. Stephan, Klaas E. Friston, Karl J. UCL Wellcome Trust Ctr Neuroimaging London WC1E 6BT England

The mismatch negativity (MMN) is a brain response to violations of a rule, established by a sequence of sensory stimuli (typically in the auditory domain) [Naatanen R. Attention and brain function. Hillsdale, N.J: Lawrence Erlbaum: 1992]. The MMN reflects the brain's ability to perform automatic comparisons between consecutive stimuli and provides an electrophysiological index of sensory learning and perceptual accuracy. Although the MMN has been studied extensively, the neurophysiological mechanisms underlying the MMN are not well understood. Several hypotheses have been put forward to explain the generation of the MMN: amongst these accounts, the "adaptation hypothesis" and the "model adjustment hypothesis" have received the most attention. This paper presents a review of studies that focus on neuronal mechanisms underlying the MMN generation, discusses the two major explanatory hypotheses, and proposes predictive coding as a general framework that attempts to unify both. (C) 2008 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

关键词： Mismatch negativity (MMN) Event-related potential (ERP) Mechanistic models Cortical networks predictive coding

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Dysconnection in Schizophrenia: From Abnormal Synaptic Plasticity to Failures of Self-monitoring

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SCHIZOPHRENIA BULLETIN 2009年第3期35卷 509-527页

作者： Stephan, Klaas E. Friston, Karl J. Frith, Chris D. UCL Inst Neurol Wellcome Trust Ctr Neuroimaging London WC1N 3BG England Univ Zurich Inst Empir Res Econ Lab Social & Neural Syst Res Zurich Switzerland Aarhus Univ Hosp CFIN DK-8000 Aarhus Denmark

Over the last 2 decades, a large number of neurophysiological and neuroimaging studies of patients with schizophrenia have furnished in vivo evidence for dysconnectivity, ie, abnormal functional integration of brain processes. While the evidence for dysconnectivity in schizophrenia is strong, its etiology, pathophysiological mechanisms, and significance for clinical symptoms are unclear. First, dysconnectivity could result from aberrant wiring of connections during development, from aberrant synaptic plasticity, or from both. Second, it is not clear how schizophrenic symptoms can be understood mechanistically as a consequence of dysconnectivity. Third, if dysconnectivity is the primary pathophysiology, and not just an epiphenomenon, then it should provide a mechanistic explanation for known empirical facts about schizophrenia. This article addresses these 3 issues in the framework of the dysconnection hypothesis. This theory postulates that the core pathology in schizophrenia resides in aberrant N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity due to abnormal regulation of NMDARs by neuromodulatory transmitters like dopamine, serotonin, or acetylcholine. We argue that this neurobiological mechanism can explain failures of self-monitoring, leading to a mechanistic explanation for first-rank symptoms as pathognomonic features of schizophrenia, and may provide a basis for future diagnostic classifications with physiologically defined patient subgroups. Finally, we test the explanatory power of our theory against a list of empirical facts about schizophrenia.

关键词： dysconnectivity corollary discharge psychosis hallucinations delusions NMDA dopamine acetylcholine serotonin effective connectivity dynamic causal modeling DCM predictive coding

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Motion Vector coding using Decoder-side Estimation of Motion Vector

Motion Vector Coding using Decoder-side Estimation of Motion...

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IEEE International Symposium on Broadband Multimedia Systems and Broadcasting

作者： Won, Kwanghyun Yang, Jungyoup Jeon, Byeungwoo Sungkyunkwan Univ Sch Informat & Comp Engn Suwon 440746 South Korea

ISBN: (纸本)9781424425907

The H.264/AVC standard employs the predictive motion vector coding technique using the median predictor of spatially neighboring three motion vectors. Although the median is effective in reducing redundancy, it is not always optimal in minimizing bits. To solve the matter, a new motion vector coding scheme, known as, MV competition in which decoder is signaled on the selected optimal PMV, has been reported. Though it can use the optimal PMV(Predicted Motion Vector), the bits consumed to indicating the optimal PMV to the decoder increases bit-rate. In this paper, we propose a new motion vector coding scheme that allows usage of an optimal PMV without consuming additional bits to inform the choice of PMV to decoder. Simulation results show that the proposed method gains in BDBR by 3.22% on average, and in BDPSNR by 0.13dB compared to the H.264/AVC.

关键词： motion vector coding predictive coding predicted motion vector template matching

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A New Steganographic Method Using Quantization Index Modulation

A New Steganographic Method Using Quantization Index Modulat...

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International Conference on Computer and Automation Engineering

作者： Izadinia, Hamid Sadeghi, Fereshteh Rahmati, Mohammad Amirkabir Univ Technol Comp Engn & Informat Technol Dept Tehran Iran

ISBN: (纸本)9780769535692

Steganography is the art and science of hiding secret data to provide a safe communication between two parties and it is a prominent branch in the information hiding research area. This paper presents a new steganographic method based on predictive coding and embeds secret message in quantized error values via Quantization Index Modulation (QIM). The proposed method is superior to previous methods in that it can make a satisfying balance among the most concerned criteria in steganography which are imperceptibility, hiding capacity, compression ratio and robustness against attacks. The performance of the proposed method is evaluated by several experiments on gray-level images with different textural properties. The new method is also compared with two renowned steganographic methods namely Jsteg and Steganography Based on predictive coding (SBPC). The results obtained from the experiments show that the proposed method has high visual quality and less histogram distortion while it has satisfactory compression ratio and embedding size.

关键词： Steganography watermarking quantization index modulation predictive coding

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Does the Scanning Pattern affect adaptive Quantization Processing?

Does the Scanning Pattern affect adaptive Quantization Proce...

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12th International Symposium on Integrated Circuits

作者： Zhang, Milin Bermak, Amine Hong Kong Univ Sci & Technol Dept Elect & Comp Engn Hong Kong Hong Kong Peoples R China

ISBN: (纸本)9789810824686

In this paper, we investigate whether different scanning pattern affect the image quality reconstructed from adaptive quantization processing. Different space filling curves, such as Peano curve, Hilbert curve, Moore curve, are implemented and compared in terms of compression ratio as well as image quality expressed in PSNR. The investigated space filling curves preserve the spacial neighborhood property of the pixel array, which is useful for predictive coding. While using those space filling curves, higher reconstructed image quality can be expected compared with the traditional raster scanning scheme.

关键词： Space filling curves predictive coding raster scan

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PCIF: An Algorithm for Lossless True Color Image Compression

PCIF: An Algorithm for Lossless True Color Image Compression

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13th International Workshop on Combinatorial Image Analysis

作者： Barcucci, Elena Brlek, Srecko Brocchi, Stefano Univ Florence Dipartimento Sistemi & Informat Viale Morgagni 65 I-50134 Florence Italy Univ Quebec Montreal LaCIM Montreal PQ H3C3P8 Canada

ISBN: (纸本)9783642102080

An efficient algorithm for compressing true color images is proposed. The technique uses a combination of simple and computationally cheap operations. The three main steps consist of predictive image filtering, decomposition of data, and data compression through the use of run length encoding, Huffman coding and grouping the values into polyominoes. The result is a practical scheme that achieves good compression while providing fast decompression. The approach has performance comparable to, and often better than, competing standards such JPEG 2000 and JPEG-LS.

关键词： Lossless compression predictive coding Huffman codes

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ATTRACTORS IN SONG

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NEW MATHEMATICS AND NATURAL COMPUTATION 2009年第1期5卷 83-114页

作者： Friston, Karl Kiebel, Stefan UCL Wellcome Trust Ctr Neuroimaging Queen Sq London WC1N 3BG England

This paper summarizes our recent attempts to integrate action and perception within a single optimization framework. We start with a statistical formulation of Helmholtz's ideas about neural energy to furnish a model of perceptual inference and learning that can explain a remarkable range of neurobiological facts. Using constructs from statistical physics it can be shown that the problems of inferring the causes of our sensory inputs and learning regularities in the sensorium can be resolved using exactly the same principles. Furthermore, inference and learning can proceed in a biologically plausible fashion. The ensuing scheme rests on Empirical Bayes and hierarchical models of how sensory information is generated. The use of hierarchical models enables the brain to construct prior expectations in a dynamic and context-sensitive fashion. This scheme provides a principled way to understand many aspects of the brain's organization and responses. We will demonstrate the brain-like dynamics that this scheme entails by using models of birdsongs that are based on chaotic attractors with autonomous dynamics. This provides a nice example of how non-linear dynamics can be exploited by the brain to represent and predict dynamics in the environment.

关键词： Generative models predictive coding hierarchical dynamic non-linear variational birdsong

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Improving multiscale recurrent pattern image coding with least-squares prediction mode

Improving multiscale recurrent pattern image coding with lea...

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IEEE International Conference on Image Processing

作者： Danillo B. Graziosi Nuno M. M. Rodrigues Eduardo A. B. da Silva Sérgio M. M. de Faria Murilo B. de Carvalho PEE/COPPE/DEL/EE Federal University of Rio de Janeiro Rio de Janeiro Brazil Instituto de Telecommunicações Portugal TET University Fed. Fluminense Brazil

The Multidimensional Multiscale Parser-based (MMP) image coding algorithm, when combined with flexible partitioning and predictive coding techniques (MMP-FP), provides state-of-the-art performance. In this paper we investigate the use of adaptive least-squares prediction in MMP. The linear prediction coefficients implicitly embed the local texture characteristics, and are computed based on a block's causal neighborhood (composed of already reconstructed data). Thus, the intra prediction mode is adaptively adjusted according to the local context and no extra overhead is needed for signaling the coefficients. We add this new context-adaptive linear prediction mode to the other MMP prediction modes, that are based on the ones used in H.264/AVC; the best mode is chosen through rate-distortion optimization. Simulation results show that least-squares prediction is able to significantly increase MMP-FPs rate-distortion performance for smooth images, leading to better results than the ones of state-of-theart, transform-based methods. Yet with the addition of least-squares prediction MMP-FP presents no performance loss when used for encoding non-smooth images, such as text and graphics.

关键词： Image coding Rate-distortion Multidimensional systems Partitioning algorithms predictive coding Embedded computing Image reconstruction Automatic voltage control predictive models Performance loss

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