1 Introduction |
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1.1 What this Book Is All About |
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1.3 The Magic of Your Visual System |
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1.4 Importance of Prior Information |
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1.4.1 Ecological Adaptation Provides Prior Information |
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1.4.2 Generative Models and Latent Quantities |
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1.4.3 Projection onto the Retina Loses Information |
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1.4.4 Bayesian Inference and Priors |
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1.5.2 Definition of Natural Images |
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1.6 Redundancy and Information |
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1.6.1 Information Theory and Image Coding |
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1.6.2 Redundancy Reduction and Neural Coding |
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1.7 Statistical Modeling of the Visual System |
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1.7.1 Connecting Information Theory and Bayesian Inference |
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1.7.2 Normative vs. Descriptive Modeling of Visual System |
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1.7.3 Toward Predictive Theoretical Neuroscience |
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1.8 Features and Statistical Models of Natural Images |
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1.8.1 Image Representations and Features |
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1.8.2 Statistics of Features |
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1.8.3 From Features to Statistical Models |
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1.9 The Statistical–Ecological Approach Recapitulated |
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Part I Background |
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2 Linear Filters and Frequency Analysis |
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2.1.2 Impulse Response and Convolution |
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2.2 Frequency-Based Representation |
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2.2.2 Representation in One and Two Dimensions |
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2.2.3 Frequency-Based Representation and Linear Filtering |
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2.2.4 Computation and Mathematical Details |
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2.3 Representation Using Linear Basis |
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2.3.2 Frequency-Based Representation as a Basis |
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2.4 Space-Frequency Analysis |
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2.4.2 Space-Frequency Analysis and Gabor Filters |
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2.4.3 Spatial Localization vs. Spectral Accuracy |
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3 Outline of the Visual System |
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3.1 Neurons and Firing Rates |
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3.2 From the Eye to the Cortex |
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3.3 Linear Models of Visual Neurons |
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3.3.1 Responses to Visual Stimulation |
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3.3.2 Simple Cells and Linear Models |
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3.3.3 Gabor Models and Selectivities of Simple Cells |
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3.4 Non-linear Models of Visual Neurons |
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3.4.1 Non-linearities in Simple-Cell Responses |
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3.4.2 Complex Cells and Energy Models |
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3.5 Interactions between Visual Neurons |
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3.6 Topographic Organization |
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3.7 Processing after the Primary Visual Cortex |
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4 Multivariate Probability and Statistics |
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4.1 Natural Images Patches as Random Vectors |
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4.2 Multivariate Probability Distributions |
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4.2.1 Notation and Motivation |
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4.2.2 Probability Density Function |
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4.3 Marginal and Joint Probabilities |
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4.4 Conditional Probabilities |
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4.6 Expectation and Covariance |
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4.6.2 Variance and Covariance in One Dimension |
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4.6.4 Independence and Covariances |
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4.7.3 Non-informative Priors |
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4.7.4 Bayesian Inference as an Incremental Learning Process |
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4.8 Parameter Estimation and Likelihood |
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4.8.1 Models, Estimation, and Samples |
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4.8.2 Maximum Likelihood and Maximum a Posteriori |
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4.8.3 Prior and Large Samples |
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Part II Statistics of Linear Features |
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5 Principal Components and Whitening |
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5.1 DC Component or Mean Grey-Scale Value |
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5.2 Principal Component Analysis |
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5.2.1 A Basic Dependency of Pixels in Natural Images |
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5.2.2 Learning One Feature by Maximization of Variance |
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5.2.3 Learning Many Features by PCA |
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5.2.4 Computational Implementation of PCA |
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5.2.5 The Implications of Translation-Invariance |
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5.3 PCA as a Preprocessing Tool |
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5.3.1 Dimension Reduction by PCA |
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5.3.3 Anti-aliasing by PCA |
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5.4 Canonical Preprocessing Used in This Book |
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5.5 Gaussianity as the Basis for PCA |
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5.5.1 The Probability Model Related to PCA |
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5.5.2 PCA as a Generative Model |
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5.5.3 Image Synthesis Results |
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5.6 Power Spectrum of Natural Images |
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5.6.1 The 1 /f Fourier Amplitude or 1/1'2 Power Spectrum |
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5.6.2 Connection between Power Spectrum and Covariances |
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5.6.3 Relative Importance of Amplitude and Phase |
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5.7 Anisotropy in Natural Images |
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5.8 Mathematics of Principal Component Analysis* |
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5.8.1 Eigenvalue Decomposition of the Covariance Matrix |
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5.8.2 Eigenvectors and Translation-Invariance |
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5.9 Decorrelation Models of Retina and LGN |
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5.9.1 Whitening and Redundancy Reduction |
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5.9.2 Patch-Based Decorrelation |
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5.9.3 Filter-Based Decorrelation |
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5.10 Concluding Remarks and References |
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6 Sparse Coding and Simple Cells |
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6.1 Definition of Sparseness |
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6.2 Learning One Feature by Maximization of Sparseness |
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6.2.1 Measuring Sparseness: General Framework |
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6.2.2 Measuring Sparseness Using Kurtosis |
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6.2.3 Measuring Sparseness Using Convex Functions of Square |
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6.2.4 The Case of Canonically Preprocessed Data |
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6.2.5 One Feature Learned from Natural Images |
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6.3 Learning Many Features by Maximization of Sparseness |
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6.3.1 Deflationary Decorrelation |
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6.3.2 Symmetric Decorrelation |
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6.3.3 Sparseness of Feature vs. Sparseness of Representation |
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6.4 Sparse Coding Features for Natural Images |
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6.4.1 Full Set of Features |
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6.4.2 Analysis of Tuning Properties |
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6.5 How Is Sparseness Useful? |
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6.6 Concluding Remarks and References |
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7 Independent Component Analysis |
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7.1 Limitations of the Sparse Coding Approach |
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7.2.3 Model for Preprocessed Data |
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7.3 Insufficiency of Second-Order Information |
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7.3.1 Why Whitening Does Not Find Independent Components |
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7.3.2 Why Components Have to Be Non-Gaussian |
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7.4 The Probability Density Defined by ICA |
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7.5 Maximum Likelihood Estimation in ICA |
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7.6 Results on Natural Images |
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7.6.1 Estimation of Features |
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7.6.2 Image Synthesis Using ICA |
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7.7 Connection to Maximization of Sparseness |
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7.7.1 Likelihood as a Measure of Sparseness |
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7.7.2 Optimal Sparseness Measures |
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7.8 Why Are Independent Components Sparse |
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7.8.1 Different Forms of Non-Gaussianity |
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7.8.2 Non-Gaussianity in Natural Images |
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7.8.3 Why Is Sparseness Dominant? |
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7.9 General ICA as Maximization of Non-Gaussianity |
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7.9.1 Central Limit Theorem |
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7.9.2 "Non-Gaussian Is Independent" |
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7.9.3 Sparse Coding as a Special Case of ICA |
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7.10 Receptive Fields vs. Feature Vectors |
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7.11 Problem of Inversion of Preprocessing |
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7.12 Frequency Channels and ICA |
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7.13 Concluding Remarks and References |
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8 Information-Theoretic Interpretations |
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8.1 Basic Motivation for Information Theory |
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8.2 Entropy as a Measure of Uncertainty |
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8.2.1 Definition of Entropy |
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8.2.2 Entropy as Minimum Coding Length |
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8.2.4 Differential Entropy |
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8.4 Minimum Entropy Coding of Natural Images |
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8.4.1 Image Compression and Sparse Coding |
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8.4.2 Mutual Information and Sparse Coding |
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8.4.3 Minimum Entropy Coding in the Cortex |
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8.5 Information Transmission in the Nervous System |
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8.5.1 Definition of Information Flow and Infomax |
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8.5.2 Basic Infomax with Linear Neurons |
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8.5.3 Infomax with Non-linear Neurons |
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8.5.4 Infomax with Non-constant Noise Variance |
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8.6 Caveats in Application of Information Theory |
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8.7 Concluding Remarks and References |
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Part III Nonlinear Features and Dependency of Linear Features |
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9 Energy Correlation of Linear Features and Normalization |
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9.1 Why Estimated Independent Components Are Not Independent |
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9.1.1 Estimates vs. Theoretical Components |
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9.1.2 Counting the Number of Free Parameters |
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9.2 Correlations of Squares of Components in Natural Images |
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9.3 Modeling Using a Variance Variable |
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9.4 Normalization of Variance and Contrast Gain Control |
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9.5 Physical and Neurophysiological Interpretations |
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9.5.1 Canceling the Effect of Changing Lighting Conditions |
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9.5.3 Saturation of Cell Responses |
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9.6 Effect of Normalization on ICA |
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9.7 Concluding Remarks and References |
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10 Energy Detectors and Complex Cells |
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10.1 Subspace Model of Invariant Features |
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10.1.1 Why Linear Features Are Insufficient |
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10.1.2 Subspaces or Groups of Linear Features |
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10.1.3 Energy Model of Feature Detection |
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10.2 Maximizing Sparseness in the Energy Model |
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10.2.1 Definition of Sparseness of Output |
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10.2.2 One Feature Learned from Natural Images |
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10.3 Model of Independent Subspace Analysis |
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10.4 Dependency as Energy Correlation |
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10.4.1 Why Energy Correlations Are Related to Sparseness |
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10.4.2 Spherical Symmetry and Changing Variance |
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10.4.3 Correlation of Squares and Convexity of Non-linearity |
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10.5 Connection to Contrast Gain Control |
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10.6 ISA as a Non-linear Version of ICA |
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10.7 Results on Natural Images |
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10.7.1 Emergence of Invariance to Phase |
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10.7.2 The Importance of Being Invariant |
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10.7.3 Grouping of Dependencies |
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10.7.4 Superiority of the Model over ICA |
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10.8 Analysis of Convexity and Energy Correlations* |
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10.8.1 Variance Variable Model Gives Convex h |
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10.8.2 Convex h Typically Implies Positive Energy Correlations |
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10.9 Concluding Remarks and References |
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11 Energy Correlations and Topographic Organization |
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11.1 Topography in the Cortex |
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11.2 Modeling Topography by Statistical Dependence |
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11.2.2 Defining Topography by Statistical Dependencies |
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11.3 Definition of Topographic ICA |
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11.4 Connection to Independent Subspaces and Invariant Features |
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11.5 Utility of Topography |
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11.6 Estimation of Topographic ICA |
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11.7 Topographic ICA of Natural Images |
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11.7.1 Emergence of V1-like Topography |
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11.7.2 Comparison with Other Models |
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11.8 Learning Both Layers in a Two-Layer Model "I' |
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11.8.1 Generative vs. Energy-Based Approach |
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11.8.2 Definition of the Generative Model |
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11.8.3 Basic Properties of the Generative Model |
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11.8.4 Estimation of the Generative Model |
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11.8.5 Energy-Based Two-Layer Models |
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11.9 Concluding Remarks and References |
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12 Dependencies of Energy Detectors: Beyond V1 |
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12.1 Predictive Modeling of Extrastriate Cortex |
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12.2 Simulation of V 1 by a Fixed Two-Layer Model |
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12.3 Learning the Third Layer by Another ICA Model |
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12.4 Methods for Analyzing Higher-Order Components |
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12.5 Results on Natural Images |
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12.5.1 Emergence of Collinear Contour Units |
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12.5.2 Emergence of Pooling over Frequencies |
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12.6 Discussion of Results |
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12.6.1 Why Coding of Contours9 |
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12.6.2 Frequency Channels and Edges |
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12.6.3 Toward Predictive Modeling |
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12.6.4 References and Related Work |
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13 Overcomplete and Non-negative Models |
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13.1.2 Definition of Generative Model |
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13.1.3 Nonlinear Computation of the Basis Coefficients |
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13.1.4 Estimation of the Basis |
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13.1.5 Approach Using Energy-Based Models |
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13.1.6 Results on Natural Images |
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13.1.7 Markov Random Field Models |
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13.2.3 Adding Sparseness Constraints |
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14 Lateral Interactions and Feedback |
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14.1 Feedback as Bayesian Inference |
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14.1.1 Example: Contour Integrator Units |
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14.1.2 Thresholding (Shrinkage) of a Sparse Code |
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14.1.3 Categorization and Top-Down Feedback |
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14.2 Overcomplete Basis and End-stopping |
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Part IV Time, Color, and Stereo |
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15 Color and Stereo Images |
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15.1 Color Image Experiments |
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15.1.2 Preprocessing and PCA |
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15.1.3 ICA Results and Discussion |
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15.2 Stereo Image Experiments |
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15.2.2 Preprocessing and PCA |
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15.2.3 ICA Results and Discussion |
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15.3.1 Color and Stereo Images |
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15.3.2 Other Modalities, Including Audition |
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16 Temporal Sequences of Natural Images |
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16.1 Natural Image Sequences and Spatiotemporal Filtering |
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16.2 Temporal and Spatiotemporal Receptive Fields |
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16.3 Second-Order Statistics |
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16.3.1 Average Spatiotemporal Power Spectrum |
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16.3.2 The Temporally Decorrelating Filter |
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16.4 Sparse Coding and ICA of Natural Image Sequences |
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16.5 Temporal Coherence in Spatial Features |
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16.5.1 Temporal Coherence and Invariant Representation |
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16.5.2 Quantifying Temporal Coherence |
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16.5.3 Interpretation as Generative Model |
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16.5.4 Experiments on Natural Image Sequences |
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16.5.5 Why Gabor-Like Features Maximize Temporal Coherence |
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16.5.6 Control Experiments |
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16.6 Spatiotemporal Energy Correlations in Linear Features |
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16.6.1 Definition of the Model |
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16.6.2 Estimation of the Model |
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16.6.3 Experiments on Natural Images |
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16.6.4 Intuitive Explanation of Results |
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16.7 Unifying Model of Spatiotemporal Dependencies |
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16.8 Features with Minimal Average Temporal Change |
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16.8.1 Slow Feature Analysis |
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16.8.2 Quadratic Slow Feature Analysis |
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16.8.3 Sparse Slow Feature Analysis |
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Part V Conclusion |
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17 Conclusion and Future Prospects |
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17.2 Open, or Frequently Asked, Questions |
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17.2.1 What Is the Real Learning Principle in the Brain? |
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17.2.2 Nature vs. Nurture |
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368 | |
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17.2.3 How to Model Whole Images |
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369 | |
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17.2.4 Arc There Clear-Cut Cell Types? |
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369 | |
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17.2.5 How Far Can We Go? |
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371 | |
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17.3 Other Mathematical Models of Images |
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371 | |
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372 | |
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372 | |
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17.3.3 Physically Inspired Models |
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373 | |
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374 | |
Part VI Appendix: Supplementary Mathematical Tools |
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18 Optimization Theory and Algorithms |
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377 | |
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377 | |
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378 | |
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18.2.1 Definition and Meaning of Gradient |
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378 | |
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18.2.2 Gradient and Optimization |
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380 | |
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18.2.3 Optimization of Function of Matrix |
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381 | |
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18.2.4 Constrained Optimization |
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381 | |
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18.3 Global and Local Maxima |
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383 | |
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18.4 Hebb's Rule and Gradient Methods |
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384 | |
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384 | |
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18.4.2 Hebb's Rule and Optimization |
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385 | |
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18.4.3 Stochastic Gradient Methods |
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386 | |
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18.4.4 Role of the Hebbian Non-linearity |
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387 | |
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18.4.5 Receptive Fields vs. Synaptic Strengths |
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388 | |
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18.4.6 The Problem of Feedback |
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388 | |
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18.5 Optimization in Topographic ICA * |
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389 | |
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18.6 Beyond Basic Gradient Methods* |
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390 | |
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391 | |
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18.6.2 Conjugate Gradient Methods |
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393 | |
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18.7 FastICA, a Fixed-Point Algorithm for ICA |
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394 | |
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18.7.1 The FastICA Algorithm |
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394 | |
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18.7.2 Choice of the FastICA Non-linearity |
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395 | |
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18.7.3 Mathematics of FastICA* |
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395 | |
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19 Crash Course on Linear Algebra |
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399 | |
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399 | |
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19.2 Linear Transformations |
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400 | |
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401 | |
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402 | |
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402 | |
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19.6 Basis Representations |
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403 | |
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404 | |
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405 | |
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20 The Discrete Fourier Transform |
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407 | |
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20.1 Linear Shift-Invariant Systems |
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407 | |
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20.2 One-Dimensional Discrete Fourier Transform |
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408 | |
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408 | |
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20.2.2 Representation in Complex Exponentials |
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408 | |
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20.2.3 The Discrete Fourier Transform and Its Inverse |
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411 | |
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20.3 Two- and Three-Dimensional Discrete Fourier Transforms |
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417 | |
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21 Estimation of Non-normalized Statistical Models |
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419 | |
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21.1 Non-normalized Statistical Models |
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419 | |
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21.2 Estimation by Score Matching |
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420 | |
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21.3 Example 1: Multivariate Gaussian Density |
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422 | |
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21.4 Example 2: Estimation of Basic ICA Model |
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424 | |
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21.5 Example 3: Estimation of an Overcomplete ICA Model |
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425 | |
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425 | |
References |
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427 | |
Index |
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441 | |