mtybilly/Instruct2DS huggingface dataset:
Kernel Measures of Independence for non-iid Data
Authors: Xinhua Zhang, Le Song, Arthur Gretton, Alex J. Smola
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Many machine learning algorithms can be formulated in the framework of statistical independence such as the Hilbert Schmidt Independence Criterion. In this paper, we extend this criterion to deal with with structured and interdependent observations. This is achieved by modeling the structures using undirected graphical models and comparing the Hilbert space embeddings of distributions. We apply this new criterion to independent component analysis and sequence clustering.
Regularized Policy Iteration
Authors: Amir M. Farahmand, Mohammad Ghavamzadeh, Shie Mannor, Csaba Szepesvári
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: In this paper we consider approximate policy-iteration-based reinforcement learning algorithms. In order to implement a flexible function approximation scheme we propose the use of non-parametric methods with regularization, providing a convenient way to control the complexity of the function approximator. We propose two novel regularized policy iteration algorithms by adding L2-regularization to two widely-used policy evaluation methods: Bellman residual minimization (BRM) and least-squares temporal difference learning (LSTD). We derive efficient implementation for our algorithms when the approximate value-functions belong to a reproducing kernel Hilbert space. We also provide finite-sample performance bounds for our algorithms and show that they are able to achieve optimal rates of convergence under the studied conditions.
Dimensionality Reduction for Data in Multiple Feature Representations
Authors: Yen-yu Lin, Tyng-luh Liu, Chiou-shann Fuh
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: In solving complex visual learning tasks, adopting multiple descriptors to more precisely characterize the data has been a feasible way for improving performance. These representations are typically high dimensional and assume diverse forms. Thus finding a way to transform them into a unified space of lower dimension generally facilitates the underlying tasks, such as object recognition or clustering. We describe an approach that incorporates multiple kernel learning with dimensionality reduction (MKL-DR). While the proposed framework is flexible in simultaneously tackling data in various feature representations, the formulation itself is general in that it is established upon graph embedding. It follows that any dimensionality reduction techniques explainable by graph embedding can be generalized by our method to consider data in multiple feature representations.
Continuously-adaptive discretization for message-passing algorithms
Authors: Michael Isard, John MacCormick, Kannan Achan
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Continuously-Adaptive Discretization for Message-Passing (CAD-MP) is a new message-passing algorithm employing adaptive discretization. Most previous message-passing algorithms approximated arbitrary continuous probability distributions using either: a family of continuous distributions such as the exponential family; a particle-set of discrete samples; or a fixed, uniform discretization. In contrast, CAD-MP uses a discretization that is (i) non-uniform, and (ii) adaptive. The non-uniformity allows CAD-MP to localize interesting features (such as sharp peaks) in the marginal belief distributions with time complexity that scales logarithmically with precision, as opposed to uniform discretization which scales at best linearly. We give a principled method for altering the non-uniform discretization according to information-based measures. CAD-MP is shown in experiments on simulated data to estimate marginal beliefs much more precisely than competing approaches for the same computational expense.
On Computational Power and the Order-Chaos Phase Transition in Reservoir Computing
Authors: Benjamin Schrauwen, Lars Buesing, Robert A. Legenstein
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Randomly connected recurrent neural circuits have proven t o be very powerful models for online computations when a trained memoryless re adout function is appended. Such Reservoir Computing (RC) systems are commonly used in two flavors: with analog or binary (spiking) neurons in the recur rent circuits. Previous work showed a fundamental difference between these two incarnations of the RC idea. The performance of a RC system built from binary neuron s seems to depend strongly on the network connectivity structure. In network s of analog neurons such dependency has not been observed. In this article we investigate this apparent dichotomy in terms of the in-degree of the circuit nodes. Our analyses based amongst others on the Lyapunov exponent reveal that the phase transition between ordered and chaotic network behavior of binary circuits qua litatively differs from the one in analog circuits. This explains the observed decre ased computational performance of binary circuits of high node in-degree. Furt hermore, a novel mean-field predictor for computational performance is intr oduced and shown to accurately predict the numerically obtained results.
Mind the Duality Gap: Logarithmic regret algorithms for online optimization
Authors: Shai Shalev-shwartz, Sham M. Kakade
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We describe a primal-dual framework for the design and analysis of online strongly convex optimization algorithms. Our framework yields the tightest known logarithmic regret bounds for Follow-The-Leader and for the gradient descent algorithm proposed in HazanKaKaAg06. We then show that one can interpolate between these two extreme cases. In particular, we derive a new algorithm that shares the computational simplicity of gradient descent but achieves lower regret in many practical situations. Finally, we further extend our framework for generalized strongly convex functions.
Hierarchical Semi-Markov Conditional Random Fields for Recursive Sequential Data
Authors: Tran T. Truyen, Dinh Phung, Hung Bui, Svetha Venkatesh
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Inspired by the hierarchical hidden Markov models (HHMM), we present the hierarchical semi-Markov conditional random field (HSCRF), a generalisation of embedded undirected Markov chains to model complex hierarchical, nested Markov processes. It is parameterised in a discriminative framework and has polynomial time algorithms for learning and inference. Importantly, we develop efficient algorithms for learning and constrained inference in a partially-supervised setting, which is important issue in practice where labels can only be obtained sparsely. We demonstrate the HSCRF in two applications: (i) recognising human activities of daily living (ADLs) from indoor surveillance cameras, and (ii) noun-phrase chunking. We show that the HSCRF is capable of learning rich hierarchical models with reasonable accuracy in both fully and partially observed data cases.
A spatially varying two-sample recombinant coalescent, with applications to HIV escape response
Authors: Alexander Braunstein, Zhi Wei, Shane T. Jensen, Jon D. Mcauliffe
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Statistical evolutionary models provide an important mechanism for describing and understanding the escape response of a viral population under a particular therapy. We present a new hierarchical model that incorporates spatially varying mutation and recombination rates at the nucleotide level. It also maintains sep- arate parameters for treatment and control groups, which allows us to estimate treatment effects explicitly. We use the model to investigate the sequence evolu- tion of HIV populations exposed to a recently developed antisense gene therapy, as well as a more conventional drug therapy. The detection of biologically rele- vant and plausible signals in both therapy studies demonstrates the effectiveness of the method.
Measures of Clustering Quality: A Working Set of Axioms for Clustering
Authors: Shai Ben-David, Margareta Ackerman
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Aiming towards the development of a general clustering theory, we discuss abstract axiomatization for clustering. In this respect, we follow up on the work of Kelinberg, (Kleinberg) that showed an impossibility result for such axiomatization. We argue that an impossibility result is not an inherent feature of clustering, but rather, to a large extent, it is an artifact of the specific formalism used in Kleinberg. As opposed to previous work focusing on clustering functions, we propose to address clustering quality measures as the primitive object to be axiomatized. We show that principles like those formulated in Kleinberg's axioms can be readily expressed in the latter framework without leading to inconsistency. A clustering-quality measure is a function that, given a data set and its partition into clusters, returns a non-negative real number representing how strong' orconclusive' the clustering is. We analyze what clustering-quality measures should look like and introduce a set of requirements (`axioms') that express these requirement and extend the translation of Kleinberg's axioms to our framework. We propose several natural clustering quality measures, all satisfying the proposed axioms. In addition, we show that the proposed clustering quality can be computed in polynomial time.
Structure Learning in Human Sequential Decision-Making
Authors: Daniel Acuna, Paul R. Schrater
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We use graphical models and structure learning to explore how people learn policies in sequential decision making tasks. Studies of sequential decision-making in humans frequently find suboptimal performance relative to an ideal actor that knows the graph model that generates reward in the environment. We argue that the learning problem humans face also involves learning the graph structure for reward generation in the environment. We formulate the structure learning problem using mixtures of reward models, and solve the optimal action selection problem using Bayesian Reinforcement Learning. We show that structure learning in one and two armed bandit problems produces many of the qualitative behaviors deemed suboptimal in previous studies. Our argument is supported by the results of experiments that demonstrate humans rapidly learn and exploit new reward structure.
Effects of Stimulus Type and of Error-Correcting Code Design on BCI Speller Performance
Authors: Jeremy Hill, Jason Farquhar, Suzanna Martens, Felix Biessmann, Bernhard Schölkopf
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: From an information-theoretic perspective, a noisy transmission system such as a visual Brain-Computer Interface (BCI) speller could benefit from the use of error-correcting codes. However, optimizing the code solely according to the maximal minimum-Hamming-distance criterion tends to lead to an overall increase in target frequency of target stimuli, and hence a significantly reduced average target-to-target interval (TTI), leading to difficulties in classifying the individual event-related potentials (ERPs) due to overlap and refractory effects. Clearly any change to the stimulus setup must also respect the possible psychophysiological consequences. Here we report new EEG data from experiments in which we explore stimulus types and codebooks in a within-subject design, finding an interaction between the two factors. Our data demonstrate that the traditional, row-column code has particular spatial properties that lead to better performance than one would expect from its TTIs and Hamming-distances alone, but nonetheless error-correcting codes can improve performance provided the right stimulus type is used.
Supervised Dictionary Learning
Authors: Julien Mairal, Jean Ponce, Guillermo Sapiro, Andrew Zisserman, Francis R. Bach
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: It is now well established that sparse signal models are well suited to restoration tasks and can effectively be learned from audio, image, and video data. Recent research has been aimed at learning discriminative sparse models instead of purely reconstructive ones. This paper proposes a new step in that direction with a novel sparse representation for signals belonging to different classes in terms of a shared dictionary and multiple decision functions. It is shown that the linear variant of the model admits a simple probabilistic interpretation, and that its most general variant also admits a simple interpretation in terms of kernels. An optimization framework for learning all the components of the proposed model is presented, along with experiments on standard handwritten digit and texture classification tasks.
Natural Image Denoising with Convolutional Networks
Authors: Viren Jain, Sebastian Seung
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We present an approach to low-level vision that combines two main ideas: the use of convolutional networks as an image processing architecture and an unsupervised learning procedure that synthesizes training samples from specific noise models. We demonstrate this approach on the challenging problem of natural image denoising. Using a test set with a hundred natural images, we find that convolutional networks provide comparable and in some cases superior performance to state of the art wavelet and Markov random field (MRF) methods. Moreover, we find that a convolutional network offers similar performance in the blind denoising setting as compared to other techniques in the non-blind setting. We also show how convolutional networks are mathematically related to MRF approaches by presenting a mean field theory for an MRF specially designed for image denoising. Although these approaches are related, convolutional networks avoid computational difficulties in MRF approaches that arise from probabilistic learning and inference. This makes it possible to learn image processing architectures that have a high degree of representational power (we train models with over 15,000 parameters), but whose computational expense is significantly less than that associated with inference in MRF approaches with even hundreds of parameters.
Optimal Response Initiation: Why Recent Experience Matters
Authors: Matt Jones, Sachiko Kinoshita, Michael Mozer
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: In most cognitive and motor tasks, speed-accuracy tradeoffs are observed: Individuals can respond slowly and accurately, or quickly yet be prone to errors. Control mechanisms governing the initiation of behavioral responses are sensitive not only to task instructions and the stimulus being processed, but also to the recent stimulus history. When stimuli can be characterized on an easy-hard dimension (e.g., word frequency in a naming task), items preceded by easy trials are responded to more quickly, and with more errors, than items preceded by hard trials. We propose a rationally motivated mathematical model of this sequential adaptation of control, based on a diffusion model of the decision process in which difficulty corresponds to the drift rate for the correct response. The model assumes that responding is based on the posterior distribution over which response is correct, conditioned on the accumulated evidence. We derive this posterior as a function of the drift rate, and show that higher estimates of the drift rate lead to (normatively) faster responding. Trial-by-trial tracking of difficulty thus leads to sequential effects in speed and accuracy. Simulations show the model explains a variety of phenomena in human speeded decision making. We argue this passive statistical mechanism provides a more elegant and parsimonious account than extant theories based on elaborate control structures.
Bayesian Experimental Design of Magnetic Resonance Imaging Sequences
Authors: Hannes Nickisch, Rolf Pohmann, Bernhard Schölkopf, Matthias Seeger
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We show how improved sequences for magnetic resonance imaging can be found through automated optimization of Bayesian design scores. Combining recent advances in approximate Bayesian inference and natural image statistics with high-performance numerical computation, we propose the first scalable Bayesian experimental design framework for this problem of high relevance to clinical and brain research. Our solution requires approximate inference for dense, non-Gaussian models on a scale seldom addressed before. We propose a novel scalable variational inference algorithm, and show how powerful methods of numerical mathematics can be modified to compute primitives in our framework. Our approach is evaluated on a realistic setup with raw data from a 3T MR scanner.
Temporal Dynamics of Cognitive Control
Authors: Jeremy Reynolds, Michael Mozer
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Cognitive control refers to the flexible deployment of memory and attention in response to task demands and current goals. Control is often studied experimentally by presenting sequences of stimuli, some demanding a response, and others modulating the stimulus-response mapping. In these tasks, participants must maintain information about the current stimulus-response mapping in working memory. Prominent theories of cognitive control use recurrent neural nets to implement working memory, and optimize memory utilization via reinforcement learning. We present a novel perspective on cognitive control in which working memory representations are intrinsically probabilistic, and control operations that maintain and update working memory are dynamically determined via probabilistic inference. We show that our model provides a parsimonious account of behavioral and neuroimaging data, and suggest that it offers an elegant conceptualization of control in which behavior can be cast as optimal, subject to limitations on learning and the rate of information processing. Moreover, our model provides insight into how task instructions can be directly translated into appropriate behavior and then efficiently refined with subsequent task experience.
Overlaying classifiers: a practical approach for optimal ranking
Authors: Stéphan J. Clémençcon, Nicolas Vayatis
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: ROC curves are one of the most widely used displays to evaluate performance of scoring functions. In the paper, we propose a statistical method for directly optimizing the ROC curve. The target is known to be the regression function up to an increasing transformation and this boils down to recovering the level sets of the latter. We propose to use classifiers obtained by empirical risk minimization of a weighted classification error and then to construct a scoring rule by overlaying these classifiers. We show the consistency and rate of convergence to the optimal ROC curve of this procedure in terms of supremum norm and also, as a byproduct of the analysis, we derive an empirical estimate of the optimal ROC curve.
Model selection and velocity estimation using novel priors for motion patterns
Authors: Shuang Wu, Hongjing Lu, Alan L. Yuille
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Psychophysical experiments show that humans are better at perceiving rotation and expansion than translation. These findings are inconsistent with standard models of motion integration which predict best performance for translation [6]. To explain this discrepancy, our theory formulates motion perception at two levels of inference: we first perform model selection between the competing models (e.g. translation, rotation, and expansion) and then estimate the velocity using the selected model. We define novel prior models for smooth rotation and expansion using techniques similar to those in the slow-and-smooth model [17] (e.g. Green functions of differential operators). The theory gives good agreement with the trends observed in human experiments.
On the Reliability of Clustering Stability in the Large Sample Regime
Authors: Ohad Shamir, Naftali Tishby
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Clustering stability is an increasingly popular family of methods for performing model selection in data clustering. The basic idea is that the chosen model should be stable under perturbation or resampling of the data. Despite being reasonably effective in practice, these methods are not well understood theoretically, and present some difficulties. In particular, when the data is assumed to be sampled from an underlying distribution, the solutions returned by the clustering algorithm will usually become more and more stable as the sample size increases. This raises a potentially serious practical difficulty with these methods, because it means there might be some hard-to-compute sample size, beyond which clustering stability estimators 'break down' and become unreliable in detecting the most stable model. Namely, all models will be relatively stable, with differences in their stability measures depending mostly on random and meaningless sampling artifacts. In this paper, we provide a set of general sufficient conditions, which ensure the reliability of clustering stability estimators in the large sample regime. In contrast to previous work, which concentrated on specific toy distributions or specific idealized clustering frameworks, here we make no such assumptions. We then exemplify how these conditions apply to several important families of clustering algorithms, such as maximum likelihood clustering, certain types of kernel clustering, and centroid-based clustering with any Bregman divergence. In addition, we explicitly derive the non-trivial asymptotic behavior of these estimators, for any framework satisfying our conditions. This can help us understand what is considered a 'stable' model by these estimators, at least for large enough samples.
Using matrices to model symbolic relationship
Authors: Ilya Sutskever, Geoffrey E. Hinton
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We describe a way of learning matrix representations of objects and relationships. The goal of learning is to allow multiplication of matrices to represent symbolic relationships between objects and symbolic relationships between relationships, which is the main novelty of the method. We demonstrate that this leads to excellent generalization in two different domains: modular arithmetic and family relationships. We show that the same system can learn first-order propositions such as $(2, 5) \member +\!3$ or $(Christopher, Penelope)\member has\_wife$, and higher-order propositions such as $(3, +\!3) \member plus$ and $(+\!3, -\!3) \member inverse$ or $(has\_husband, has\_wife)\in higher\_oppsex$. We further demonstrate that the system understands how higher-order propositions are related to first-order ones by showing that it can correctly answer questions about first-order propositions involving the relations $+\!3$ or $has\_wife$ even though it has not been trained on any first-order examples involving these relations.
Characteristic Kernels on Groups and Semigroups
Authors: Kenji Fukumizu, Arthur Gretton, Bernhard Schölkopf, Bharath K. Sriperumbudur
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Embeddings of random variables in reproducing kernel Hilbert spaces (RKHSs) may be used to conduct statistical inference based on higher order moments. For sufficiently rich (characteristic) RKHSs, each probability distribution has a unique embedding, allowing all statistical properties of the distribution to be taken into consideration. Necessary and sufficient conditions for an RKHS to be characteristic exist for $\R^n$. In the present work, conditions are established for an RKHS to be characteristic on groups and semigroups. Illustrative examples are provided, including characteristic kernels on periodic domains, rotation matrices, and $\R^n_+$.
Multi-label Multiple Kernel Learning
Authors: Shuiwang Ji, Liang Sun, Rong Jin, Jieping Ye
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We present a multi-label multiple kernel learning (MKL) formulation, in which the data are embedded into a low-dimensional space directed by the instance-label correlations encoded into a hypergraph. We formulate the problem in the kernel-induced feature space and propose to learn the kernel matrix as a linear combination of a given collection of kernel matrices in the MKL framework. The proposed learning formulation leads to a non-smooth min-max problem, and it can be cast into a semi-infinite linear program (SILP). We further propose an approximate formulation with a guaranteed error bound which involves an unconstrained and convex optimization problem. In addition, we show that the objective function of the approximate formulation is continuously differentiable with Lipschitz gradient, and hence existing methods can be employed to compute the optimal solution efficiently. We apply the proposed formulation to the automated annotation of Drosophila gene expression pattern images, and promising results have been reported in comparison with representative algorithms.
Bio-inspired Real Time Sensory Map Realignment in a Robotic Barn Owl
Authors: Juan Huo, Zhijun Yang, Alan F. Murray
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: The visual and auditory map alignment in the Superior Colliculus (SC) of barn owl is important for its accurate localization for prey behavior. Prism learning or Blindness may interfere this alignment and cause loss of the capability of accurate prey. However, juvenile barn owl could recover its sensory map alignment by shifting its auditory map. The adaptation of this map alignment is believed based on activity dependent axon developing in Inferior Colliculus (IC). A model is built to explore this mechanism. In this model, axon growing process is instructed by an inhibitory network in SC while the strength of the inhibition adjusted by Spike Timing Dependent Plasticity (STDP). We test and analyze this mechanism by application of the neural structures involved in spatial localization in a robotic system.
Spectral Hashing
Authors: Yair Weiss, Antonio Torralba, Rob Fergus
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Semantic hashing seeks compact binary codes of datapoints so that the Hamming distance between codewords correlates with semantic similarity. Hinton et al. used a clever implementation of autoencoders to find such codes. In this paper, we show that the problem of finding a best code for a given dataset is closely related to the problem of graph partitioning and can be shown to be NP hard. By relaxing the original problem, we obtain a spectral method whose solutions are simply a subset of thresh- olded eigenvectors of the graph Laplacian. By utilizing recent results on convergence of graph Laplacian eigenvectors to the Laplace-Beltrami eigen- functions of manifolds, we show how to efficiently calculate the code of a novel datapoint. Taken together, both learning the code and applying it to a novel point are extremely simple. Our experiments show that our codes significantly outperform the state-of-the art.
Multi-resolution Exploration in Continuous Spaces
Authors: Ali Nouri, Michael L. Littman
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: The essence of exploration is acting to try to decrease uncertainty. We propose a new methodology for representing uncertainty in continuous-state control problems. Our approach, multi-resolution exploration (MRE), uses a hierarchical mapping to identify regions of the state space that would benefit from additional samples. We demonstrate MRE's broad utility by using it to speed up learning in a prototypical model-based and value-based reinforcement-learning method. Empirical results show that MRE improves upon state-of-the-art exploration approaches.
A computational model of hippocampal function in trace conditioning
Authors: Elliot A. Ludvig, Richard S. Sutton, Eric Verbeek, E. J. Kehoe
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We present a new reinforcement-learning model for the role of the hippocampus in classical conditioning, focusing on the differences between trace and delay conditioning. In the model, all stimuli are represented both as unindividuated wholes and as a series of temporal elements with varying delays. These two stimulus representations interact, producing different patterns of learning in trace and delay conditioning. The model proposes that hippocampal lesions eliminate long-latency temporal elements, but preserve short-latency temporal elements. For trace conditioning, with no contiguity between stimulus and reward, these long-latency temporal elements are vital to learning adaptively timed responses. For delay conditioning, in contrast, the continued presence of the stimulus supports conditioned responding, and the short-latency elements suppress responding early in the stimulus. In accord with the empirical data, simulated hippocampal damage impairs trace conditioning, but not delay conditioning, at medium-length intervals. With longer intervals, learning is impaired in both procedures, and, with shorter intervals, in neither. In addition, the model makes novel predictions about the response topography with extended stimuli or post-training lesions. These results demonstrate how temporal contiguity, as in delay conditioning, changes the timing problem faced by animals, rendering it both easier and less susceptible to disruption by hippocampal lesions.
Online Prediction on Large Diameter Graphs
Authors: Mark Herbster, Guy Lever, Massimiliano Pontil
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Current on-line learning algorithms for predicting the labelling of a graph have an important limitation in the case of large diameter graphs; the number of mistakes made by such algorithms may be proportional to the square root of the number of vertices, even when tackling simple problems. We overcome this problem with an efficient algorithm which achieves a logarithmic mistake bound. Furthermore, current algorithms are optimised for data which exhibits cluster-structure; we give an additional algorithm which performs well locally in the presence of cluster structure and on large diameter graphs.
Sparse probabilistic projections
Authors: Cédric Archambeau, Francis R. Bach
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We present a generative model for performing sparse probabilistic projections, which includes sparse principal component analysis and sparse canonical correlation analysis as special cases. Sparsity is enforced by means of automatic relevance determination or by imposing appropriate prior distributions, such as generalised hyperbolic distributions. We derive a variational Expectation-Maximisation algorithm for the estimation of the hyperparameters and show that our novel probabilistic approach compares favourably to existing techniques. We illustrate how the proposed method can be applied in the context of cryptoanalysis as a pre-processing tool for the construction of template attacks.
Sparsity of SVMs that use the epsilon-insensitive loss
Authors: Ingo Steinwart, Andreas Christmann
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: In this paper lower and upper bounds for the number of support vectors are derived for support vector machines (SVMs) based on the epsilon-insensitive loss function. It turns out that these bounds are asymptotically tight under mild assumptions on the data generating distribution. Finally, we briefly discuss a trade-off in epsilon between sparsity and accuracy if the SVM is used to estimate the conditional median.
Automatic online tuning for fast Gaussian summation
Authors: Vlad I. Morariu, Balaji V. Srinivasan, Vikas C. Raykar, Ramani Duraiswami, Larry S. Davis
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Many machine learning algorithms require the summation of Gaussian kernel functions, an expensive operation if implemented straightforwardly. Several methods have been proposed to reduce the computational complexity of evaluating such sums, including tree and analysis based methods. These achieve varying speedups depending on the bandwidth, dimension, and prescribed error, making the choice between methods difficult for machine learning tasks. We provide an algorithm that combines tree methods with the Improved Fast Gauss Transform (IFGT). As originally proposed the IFGT suffers from two problems: (1) the Taylor series expansion does not perform well for very low bandwidths, and (2) parameter selection is not trivial and can drastically affect performance and ease of use. We address the first problem by employing a tree data structure, resulting in four evaluation methods whose performance varies based on the distribution of sources and targets and input parameters such as desired accuracy and bandwidth. To solve the second problem, we present an online tuning approach that results in a black box method that automatically chooses the evaluation method and its parameters to yield the best performance for the input data, desired accuracy, and bandwidth. In addition, the new IFGT parameter selection approach allows for tighter error bounds. Our approach chooses the fastest method at negligible additional cost, and has superior performance in comparisons with previous approaches.
Reducing statistical dependencies in natural signals using radial Gaussianization
Authors: Siwei Lyu, Eero P. Simoncelli
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We consider the problem of efficiently encoding a signal by transforming it to a new representation whose components are statistically independent. A widely studied linear solution, independent components analysis (ICA), exists for the case when the signal is generated as a linear transformation of independent non- Gaussian sources. Here, we examine a complementary case, in which the source is non-Gaussian but elliptically symmetric. In this case, no linear transform suffices to properly decompose the signal into independent components, but we show that a simple nonlinear transformation, which we call radial Gaussianization (RG), is able to remove all dependencies. We then demonstrate this methodology in the context of natural signal statistics. We first show that the joint distributions of bandpass filter responses, for both sound and images, are better described as elliptical than linearly transformed independent sources. Consistent with this, we demonstrate that the reduction in dependency achieved by applying RG to either pairs or blocks of bandpass filter responses is significantly greater than that achieved by PCA or ICA.
A Transductive Bound for the Voted Classifier with an Application to Semi-supervised Learning
Authors: Massih R. Amini, Nicolas Usunier, François Laviolette
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: In this paper we present two transductive bounds on the risk of the majority vote estimated over partially labeled training sets. Our first bound is tight when the additional unlabeled training data are used in the cases where the voted classifier makes its errors on low margin observations and where the errors of the associated Gibbs classifier can accurately be estimated. In semi-supervised learning, considering the margin as an indicator of confidence constitutes the working hypothesis of algorithms which search the decision boundary on low density regions. In this case, we propose a second bound on the joint probability that the voted classifier makes an error over an example having its margin over a fixed threshold. As an application we are interested on self-learning algorithms which assign iteratively pseudo-labels to unlabeled training examples having margin above a threshold obtained from this bound. Empirical results on different datasets show the effectiveness of our approach compared to the same algorithm and the TSVM in which the threshold is fixed manually.
Nonrigid Structure from Motion in Trajectory Space
Authors: Ijaz Akhter, Yaser Sheikh, Sohaib Khan, Takeo Kanade
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Existing approaches to nonrigid structure from motion assume that the instantaneous 3D shape of a deforming object is a linear combination of basis shapes, which have to be estimated anew for each video sequence. In contrast, we propose that the evolving 3D structure be described by a linear combination of basis trajectories. The principal advantage of this lateral approach is that we do not need to estimate any basis vectors during computation. Instead, we show that generic bases over trajectories, such as the Discrete Cosine Transform (DCT) bases, can be used to effectively describe most real motions. This results in a significant reduction in unknowns, and corresponding stability, in estimation. We report empirical performance, quantitatively using motion capture data and qualitatively on several video sequences exhibiting nonrigid motions including piece-wise rigid motion, articulated motion, partially nonrigid motion (such as a facial expression), and highly nonrigid motion (such as a person dancing).
Transfer Learning by Distribution Matching for Targeted Advertising
Authors: Steffen Bickel, Christoph Sawade, Tobias Scheffer
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We address the problem of learning classifiers for several related tasks that may differ in their joint distribution of input and output variables. For each task, small - possibly even empty - labeled samples and large unlabeled samples are available. While the unlabeled samples reflect the target distribution, the labeled samples may be biased. We derive a solution that produces resampling weights which match the pool of all examples to the target distribution of any given task. Our work is motivated by the problem of predicting sociodemographic features for users of web portals, based on the content which they have accessed. Here, questionnaires offered to a small portion of each portal's users produce biased samples. Transfer learning enables us to make predictions even for new portals with few or no training data and improves the overall prediction accuracy.
A Convergent $O(n)$ Temporal-difference Algorithm for Off-policy Learning with Linear Function Approximation
Authors: Richard S. Sutton, Hamid R. Maei, Csaba Szepesvári
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We introduce the first temporal-difference learning algorithm that is stable with linear function approximation and off-policy training, for any finite Markov decision process, target policy, and exciting behavior policy, and whose complexity scales linearly in the number of parameters. We consider an i.i.d.\ policy-evaluation setting in which the data need not come from on-policy experience. The gradient temporal-difference (GTD) algorithm estimates the expected update vector of the TD(0) algorithm and performs stochastic gradient descent on its L_2 norm. Our analysis proves that its expected update is in the direction of the gradient, assuring convergence under the usual stochastic approximation conditions to the same least-squares solution as found by the LSTD, but without its quadratic computational complexity. GTD is online and incremental, and does not involve multiplying by products of likelihood ratios as in importance-sampling methods.
Learning Taxonomies by Dependence Maximization
Authors: Matthew Blaschko, Arthur Gretton
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We introduce a family of unsupervised algorithms, numerical taxonomy clustering, to simultaneously cluster data, and to learn a taxonomy that encodes the relationship between the clusters. The algorithms work by maximizing the dependence between the taxonomy and the original data. The resulting taxonomy is a more informative visualization of complex data than simple clustering; in addition, taking into account the relations between different clusters is shown to substantially improve the quality of the clustering, when compared with state-of-the-art algorithms in the literature (both spectral clustering and a previous dependence maximization approach). We demonstrate our algorithm on image and text data.
Finding Latent Causes in Causal Networks: an Efficient Approach Based on Markov Blankets
Authors: Jean-philippe Pellet, André Elisseeff
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Causal structure-discovery techniques usually assume that all causes of more than one variable are observed. This is the so-called causal sufficiency assumption. In practice, it is untestable, and often violated. In this paper, we present an efficient causal structure-learning algorithm, suited for causally insufficient data. Similar to algorithms such as IC* and FCI, the proposed approach drops the causal sufficiency assumption and learns a structure that indicates (potential) latent causes for pairs of observed variables. Assuming a constant local density of the data-generating graph, our algorithm makes a quadratic number of conditional-independence tests w.r.t. the number of variables. We show with experiments that our algorithm is comparable to the state-of-the-art FCI algorithm in accuracy, while being several orders of magnitude faster on large problems. We conclude that MBCS* makes a new range of causally insufficient problems computationally tractable.
Goal-directed decision making in prefrontal cortex: a computational framework
Authors: Matthew Botvinick, James An
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: Research in animal learning and behavioral neuroscience has distinguished between two forms of action control: a habit-based form, which relies on stored action values, and a goal-directed form, which forecasts and compares action outcomes based on a model of the environment. While habit-based control has been the subject of extensive computational research, the computational principles underlying goal-directed control in animals have so far received less attention. In the present paper, we advance a computational framework for goal-directed control in animals and humans. We take three empirically motivated points as founding premises: (1) Neurons in dorsolateral prefrontal cortex represent action policies, (2) Neurons in orbitofrontal cortex represent rewards, and (3) Neural computation, across domains, can be appropriately understood as performing structured probabilistic inference. On a purely computational level, the resulting account relates closely to previous work using Bayesian inference to solve Markov decision problems, but extends this work by introducing a new algorithm, which provably converges on optimal plans. On a cognitive and neuroscientific level, the theory provides a unifying framework for several different forms of goal-directed action selection, placing emphasis on a novel form, within which orbitofrontal reward representations directly drive policy selection.
Localized Sliced Inverse Regression
Authors: Qiang Wu, Sayan Mukherjee, Feng Liang
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: We developed localized sliced inverse regression for supervised dimension reduction. It has the advantages of preventing degeneracy, increasing estimation accuracy, and automatic subclass discovery in classification problems. A semisupervised version is proposed for the use of unlabeled data. The utility is illustrated on simulated as well as real data sets.
Near-optimal Regret Bounds for Reinforcement Learning
Authors: Peter Auer, Thomas Jaksch, Ronald Ortner
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: For undiscounted reinforcement learning in Markov decision processes (MDPs) we consider the total regret of a learning algorithm with respect to an optimal policy. In order to describe the transition structure of an MDP we propose a new parameter: An MDP has diameter D if for any pair of states s1,s2 there is a policy which moves from s1 to s2 in at most D steps (on average). We present a reinforcement learning algorithm with total regret O(DSAT) after T steps for any unknown MDP with S states, A actions per state, and diameter D. This bound holds with high probability. We also present a corresponding lower bound of Omega(DSAT) on the total regret of any learning algorithm. Both bounds demonstrate the utility of the diameter as structural parameter of the MDP.
Non-parametric Regression Between Manifolds
Authors: Florian Steinke, Matthias Hein
Published in: Advances in Neural Information Processing Systems 21  (NIPS 2008) (Main Conference Track), 2008

Abstract: This paper discusses non-parametric regression between Riemannian manifolds. This learning problem arises frequently in many application areas ranging from signal processing, computer vision, over robotics to computer graphics. We present a new algorithmic scheme for the solution of this general learning problem based on regularized empirical risk minimization. The regularization functional takes into account the geometry of input and output manifold, and we show that it implements a prior which is particularly natural. Moreover, we demonstrate that our algorithm performs well in a difficult surface registration problem.