Multi-Agent Discrete Search with Limited Visibility

The problem of search by multiple agents to find and localize objects arises in many important applications. In this paper, we study a class of multi-agent search problems in which each agent can access only a subset of a discrete search space, with detection performance that depends only on the location. We show that this problem can be reformulated as a minimum cost network optimization problem, and develop a fast specialized algorithm for the solution. We prove that our algorithm is correct, and has worst case computation performance that is faster than general minimum cost flow algorithms. We also address the problem where detection performance depends on both location and agent, which is known to be NP-Hard. We reduce the problem to a submodular maximization problem over a matroid, and provide an approximate algorithm with guaranteed performance. We illustrate the performance of our algorithms with simulations of search problems and compare it with other min-cost flow algorithms.Comment: The complete version of a paper that will appear in the 56th IEEE Conference on Decision and Control, Melbourne, Australia, 201

Pasado y presente

El pasado de St Patrick’s Soho Square empieza en los llamados “Penal Times”, tiempos en que estaba penado ser católico en lo que es hoy el Reino Unido y la República de Irlanda. El acto de parlamento llamado “Roman Catolic Relief Act” data de 1829. Los años inmediatamente precedentes han visto una serie de cambios que culminaron en la promulgación de la ley del 1829 por la que la restauración de la Iglesia Católica se hace posible es esas tierras. En 1792 Fr O’Leary, un franciscano irlandés, compra Carlisle House en Soho Square y transforma el interior en una iglesia Católica sin tocar el exterior. Esta transformación consiste en convertir el ábside en presbiterio así como incrementar la capacidad de la nave insertando una galería en forma de “U”. En 1891 se empieza a construir el templo definitivo que se abre al culto en 1893. No es consagrado hasta un poco después porque todavía había que pagar algunas deudas incurridas en su construcción ...Peer Reviewe

SimpleDIVA: A 3-parameter model for examining adaptation in speech and voice production

Published versio

ROI-Based Analysis of Functional Imaging Data

In this technical report, we present fMRI analysis techniques that test functional hypotheses at the region of interest (ROI) level. An SPM-compatible Matlab toolbox has been developed which allows the creation of subject-specific ROI masks based on anatomical markers and the testing of functional hypotheses on the regional response using multivariate time-series analysis techniques. The combined application of subject-specific ROI definition and region-level functional analysis is shown to appropriately compensate for inter-subject anatomical variability, offering finer localization and increased sensitivity to task-related effects than standard techniques based on whole brain normalization and voxel or cluster-level functional analysis, while providing a more direct link between discrete brain region hypotheses and the statistical analyses used to test them.National Institute of Health (R29 DC02852, ROI DC02852

Representation of Sound Categories in Auditory Cortical Maps

We used functional magnetic resonance imaging (fMRI) to investigate the representation of sound categories in human auditory cortex. Experiment 1 investigated the representation of prototypical and non-prototypical examples of a vowel sound. Listening to prototypical examples of a vowel resulted in less auditory cortical activation than listening to nonprototypical examples. Experiments 2 and 3 investigated the effects of categorization training and discrimination training with novel non-speech sounds on auditory cortical representations. The two training tasks were shown to have opposite effects on the auditory cortical representation of sounds experienced during training: discrimination training led to an increase in the amount of activation caused by the training stimuli, whereas categorization training led to decreased activation. These results indicate that the brain efficiently shifts neural resources away from regions of acoustic space where discrimination between sounds is not behaviorally important (e.g., near the center of a sound category) and toward regions where accurate discrimination is needed. The results also provide a straightforward neural account of learned aspects of categorical perception: sounds from the center of a category are more difficult to discriminate from each other than sounds near category boundaries because they are represented by fewer cells in the auditory cortical areas.National Institute on Deafness and Other Communication Disorders (R01 DC02852

Learning to Approximate a Bregman Divergence

Bregman divergences generalize measures such as the squared Euclidean distance and the KL divergence, and arise throughout many areas of machine learning. In this paper, we focus on the problem of approximating an arbitrary Bregman divergence from supervision, and we provide a well-principled approach to analyzing such approximations. We develop a formulation and algorithm for learning arbitrary Bregman divergences based on approximating their underlying convex generating function via a piecewise linear function. We provide theoretical approximation bounds using our parameterization and show that the generalization error $O_p(m^{-1/2})$ for metric learning using our framework matches the known generalization error in the strictly less general Mahalanobis metric learning setting. We further demonstrate empirically that our method performs well in comparison to existing metric learning methods, particularly for clustering and ranking problems.Comment: 19 pages, 4 figure

Changes in the McGurk Effect Across Phonetic Contexts

To investigate the process underlying audiovisual speech perception, the McGurk illusion was examined across a range of phonetic contexts. Two major changes were found. First, the frequency of illusory /g/ fusion percepts increased relative to the frequency of illusory /d/ fusion percepts as vowel context was shifted from /i/ to /a/ to /u/. This trend could not be explained by biases present in perception of the unimodal visual stimuli. However, the change found in the McGurk fusion effect across vowel environments did correspond systematically with changes in second format frequency patterns across contexts. Second, the order of consonants in illusory combination percepts was found to depend on syllable type. This may be due to differences occuring across syllable contexts in the timecourses of inputs from the two modalities as delaying the auditory track of a vowel-consonant stimulus resulted in a change in the order of consonants perceived. Taken together, these results suggest that the speech perception system either fuses audiovisual inputs into a visually compatible percept with a similar second formant pattern to that of the acoustic stimulus or interleaves the information from different modalities, at a phonemic or subphonemic level, based on their relative arrival times.National Institutes of Health (R01 DC02852

Theoretical study of optical fiber Raman polarizers with counterpropagating beams

The theory of two counter-propagating polarized beams interacting in a randomly birefringent fiber via the Kerr and Raman effects is developed and applied to the quantitative description of Raman polarizers in the undepleted regime. Here Raman polarizers, first reported by Martinelli et. al. [Opt. Express. 17, 947 (2009)], are understood as Raman amplifiers operating in the regime in which an initially weak unpolarized beam is converted into an amplified fully polarized beam towards the fiber output. Three parameters are selected for the characterization of a Raman polarizer: the degree of polarization of the outcoming beam, its state of polarization, and its gain. All of these parameters represent quantities that are averaged over all random polarization states of the initially unpolarized signal beam. The presented theory is computer friendly and applicable to virtually all practically relevant situations, including the case of co-propagating beams, and in particular to the undepleted as well as the depleted regimes of the Raman polarizer.Comment: 16 pages, 5 figures, to be submitted to the Journal of Lightwave Technolog