Catálogo de publicaciones - libros

A novel discriminant analysis method is presented for the face recognition problem. It has been recently shown that the predictive objectives based on Parzen estimation are advantageous for learning discriminative projections if the class distributions are complicated in the projected space. However, the existing algorithms based on Parzen estimators require expensive computation to obtain the gradient for optimization. We propose here an accelerating technique by reformulating the gradient and implement its computation by matrix products. Furthermore, we point out that regularization is necessary for high-dimensional face recognition problems. The discriminative objective is therefore extended by a smoothness constraint of facial images. Our Parzen Discriminant Analysis method can be trained much faster and achieve higher recognition accuracies than the compared algorithms in experiments on two popularly used face databases.

Parts-based recognition has been suggested for generalizing from few training views in categorization scenarios. In this paper we present the results of a comparative investigation of different feature types with regard to their suitability for category discrimination. So patches of gray-scale images were compared with SIFT descriptors and patches from the high-level output of a feedforward hierarchy related to the ventral visual pathway. We discuss the conceptual differences, resulting performance and consequences for hierarchical models of visual recognition.

The goal of keyword spotting is to detect the presence of specific spoken words in unconstrained speech. The majority of keyword spotting systems are based on generative hidden Markov models and lack discriminative capabilities. However, discriminative keyword spotting systems are currently based on frame-level posterior probabilities of sub-word units. This paper presents a discriminative keyword spotting system based on recurrent neural networks only, that uses information from long time spans to estimate word-level posterior probabilities. In a keyword spotting task on a large database of unconstrained speech the system achieved a keyword spotting accuracy of 84.5%.

The spatiostructural features proposed for recognition of online handwritten characters refer to offline-like features that convey information about both the positional and structural (shape) characteristics of the handwriting unit. This paper demonstrates the effectiveness of representing an online handwritten stroke using spatiostructural features, as indicated by its effect on the stroke classification accuracy by a Support Vector Machine (SVM) based classifier. The study has been done on two major Indian writing systems, Devanagari and Tamil. The importance of localization information of the structural features and handling of translational variance is studied using appropriate approaches to zoning the handwritten character.

This paper describes an improved version of a previously developed ANOVA and Functional Networks Feature Selection method. This wrapper feature selection method is based on a functional decomposition that grows exponentially as the number of features increases. Since exponential complexity limits the scope of application of the method, a new version is proposed that subdivides this functional decomposition and increases its complexity gradually. The improved version can be applied to a broader set of data. The performance of the improved version was tested against several real datasets. The results obtained are comparable, or better, to those obtained by other standard and innovative feature selection methods.

The simultaneous determination of odor classes and concentrations is solved by a kind of parallel-series perceptron models. Two groups of parallel single-output perceptrons are in series, and the former is responsible for classification, and the latter for location. The number of parallel perceptrons is equal to the number of odor classes. A multi-class learning problem is first decomposed into multiple two-class problems, and then solved by multiple parallel perceptrons, one by one. Each training subset is composed of the most necessary samples. And furthermore, some virtual samples are added to the weak side of any two-class learning subsets in order to arrive at a virtual balance. The experimental results for 4 kinds of fragrant materials show that the proposed parallel-series perceptrons with the electronic nose are effective.

Present work introduces a probabilistic recognition scheme for hand gestures. Self organizing feature maps are used to model spatiotemporal information extracted through image processing. Two models are built for each gesture category and, along with appropriate distance metrics, produce a validated classification mechanism that performs consistently during experi-ments on acted gestures video sequences.

Classification of structured data (i.e., data that are represented as graphs) is a topic of interest in the machine learning community. This paper presents a different, simple approach to the problem of structured pattern recognition, relying on the description of graphs in terms of algebraic binary relations. Maximum-a-posteriori decision rules over relations require the estimation of class-conditional probability density functions (pdf) defined on graphs. A nonparametric technique for the estimation of the pdfs is introduced, on the basis of a factorization of joint probabilities into individual densities that are modeled, in an unsupervised fashion, via Support Vector Machine (SVM). The SVM training is accomplished applying support vector regression on an unbiased variant of the Parzen Window. The behavior of the estimation algorithm is first demonstrated on a synthetic distribution. Finally, experiments of graph-structured image recognition from the Caltech Benchmark dataset are reported, showing a dramatic improvement over the results (available in the literature) yielded by state-of-the-art connectionist models for graph processing, namely recursive neural nets and graph neural nets.

This paper describes a new model for extracting large-field optical flow patterns to generate distributed representations of neural activation to control complex visual tasks such as 3D egomotion. The neural mechanisms draw upon experimental findings about the response properties and specificities of cells in areas V1, MT and MSTd along the dorsal pathway. Model V1 cells detect local motion estimates. Model MT cells in different pools are suggested to be selective to motion patterns integrating from V1 as well as to velocity gradients. Model MSTd cells considered here integrate MT gradient cells over a much larger spatial neighborhood to generate the observed pattern selectivity for expansion/contraction, rotation and spiral motion, providing the necessary input for spatial navigation mechanisms. Our model also incorporates feedback processing between areas V1-MT and MT-MSTd. We demonstrate that such a re-entry of context-related information helps to disambiguate and stabilize more localized processing along the primary motion pathway.

In this article we present an incremental method for building a mixture model. Given the desired number of clusters  ≥ 2, we start with a two-component mixture and we optimize the likelihood by repeatedly applying a operation. When an optimum is obtained, we add a new component to the model by splitting in two, a properly chosen cluster. This goes on until the number of components reaches a preset limiting value. We have performed numerical experiments on several data–sets and report a performance comparison with other rival methods.