2,655 research outputs found
Adaptive goodness-of-fit tests in a density model
Given an i.i.d. sample drawn from a density , we propose to test that
equals some prescribed density or that belongs to some
translation/scale family. We introduce a multiple testing procedure based on an
estimation of the -distance between and or between
and the parametric family that we consider. For each sample size , our test
has level of significance . In the case of simple hypotheses, we prove
that our test is adaptive: it achieves the optimal rates of testing established
by Ingster [J. Math. Sci. 99 (2000) 1110--1119] over various classes of smooth
functions simultaneously. As for composite hypotheses, we obtain similar
results up to a logarithmic factor. We carry out a simulation study to compare
our procedures with the Kolmogorov--Smirnov tests, or with goodness-of-fit
tests proposed by Bickel and Ritov [in Nonparametric Statistics and Related
Topics (1992) 51--57] and by Kallenberg and Ledwina [Ann. Statist. 23 (1995)
1594--1608].Comment: Published at http://dx.doi.org/10.1214/009053606000000119 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The two-sample problem for Poisson processes: adaptive tests with a non-asymptotic wild bootstrap approach
Considering two independent Poisson processes, we address the question of
testing equality of their respective intensities. We first propose single tests
whose test statistics are U-statistics based on general kernel functions. The
corresponding critical values are constructed from a non-asymptotic wild
bootstrap approach, leading to level \alpha tests. Various choices for the
kernel functions are possible, including projection, approximation or
reproducing kernels. In this last case, we obtain a parametric rate of testing
for a weak metric defined in the RKHS associated with the considered
reproducing kernel. Then we introduce, in the other cases, an aggregation
procedure, which allows us to import ideas coming from model selection,
thresholding and/or approximation kernels adaptive estimation. The resulting
multiple tests are proved to be of level \alpha, and to satisfy non-asymptotic
oracle type conditions for the classical L2-norm. From these conditions, we
deduce that they are adaptive in the minimax sense over a large variety of
classes of alternatives based on classical and weak Besov bodies in the
univariate case, but also Sobolev and anisotropic Nikol'skii-Besov balls in the
multivariate case
Global gauge anomalies in coset models of conformal field theory
We study the occurrence of global gauge anomalies in the coset models of
two-dimensional conformal field theory that are based on gauged WZW models. A
complete classification of the non-anomalous theories for a wide family of
gauged rigid adjoint or twisted-adjoint symmetries of WZW models is achieved
with the help of Dynkin's classification of Lie subalgebras of simple Lie
algebras.Comment: 25 page
Bootstrap and permutation tests of independence for point processes
Motivated by a neuroscience question about synchrony detection in spike train
analysis, we deal with the independence testing problem for point processes. We
introduce non-parametric test statistics, which are rescaled general
-statistics, whose corresponding critical values are constructed from
bootstrap and randomization/permutation approaches, making as few assumptions
as possible on the underlying distribution of the point processes. We derive
general consistency results for the bootstrap and for the permutation w.r.t. to
Wasserstein's metric, which induce weak convergence as well as convergence of
second order moments. The obtained bootstrap or permutation independence tests
are thus proved to be asymptotically of the prescribed size, and to be
consistent against any reasonable alternative. A simulation study is performed
to illustrate the derived theoretical results, and to compare the performance
of our new tests with existing ones in the neuroscientific literature
Superluminality in the Bi- and Multi- Galileon
We re-explore the Bi- and Multi-Galileon models with trivial asymptotic
conditions at infinity and show that propagation of superluminal fluctuations
is a common and unavoidable feature of these theories, unlike previously
claimed in the literature. We show that all Multi-Galileon theories containing
a Cubic Galileon term exhibit superluminalities at large distances from a point
source, and that even if the Cubic Galileon is not present one can always find
sensible matter distributions in which there are superluminal modes at large
distances. In the Bi-Galileon case we explicitly show that there are always
superluminal modes around a point source even if the Cubic Galileon is not
present. Finally, we briefly comment on the possibility of avoiding
superluminalities by modifying the asymptotic conditions at infinity.Comment: 32 pages, minor changes, few references adde
Verbing and nouning in French : toward an ecologically valid approach to sentence processing
La preÌsente theÌse utilise la technique des potentiels eÌvoqueÌs afin dâeÌtudier les meÌchanismes neurocognitifs qui sous-tendent la compreÌhension de la phrase. Plus particulieÌrement, cette recherche vise aÌ clarifier lâinteraction entre les processus syntaxiques et seÌmantiques chez les locuteurs natifs et les apprenants dâune deuxieÌme langue (L2). Le modeÌle âsyntaxe en premierâ (Friederici, 2002, 2011) preÌdit que les cateÌgories syntaxiques sont analyseÌes de façon preÌcoce: ce stade est refleÌteÌ par la composante ELAN (Early anterior negativity, NeÌgativiteÌ anteÌrieure gauche), qui est induite par les erreurs de cateÌgorie syntaxique. De plus, ces erreurs semblent empeÌcher lâapparition de la composante N400 qui refleÌte les processus lexico-seÌmantiques. Ce pheÌnomeÌne est deÌfini comme le bloquage seÌmantique (Friederici et al., 1999). Cependant, la plupart des eÌtudes qui observent la ELAN utilisent des protocoles expeÌrimentaux probleÌmatiques dans lesquels les diffeÌrences entre les contextes qui preÌceÌdent la cible pourraient eÌtre aÌ lâorigine de reÌsultats fallacieux expliquant aÌ la fois lâapparente âELANâ et lâabsence de N400 (Steinhauer & Drury, 2012).
La premieÌre eÌtude reÌeÌevalue lâapproche de la âsyntaxe en premierâ en adoptant un paradigme expeÌriemental novateur en français qui introduit des erreurs de cateÌgorie syntaxique et les anomalies de seÌmantique lexicale. Ce dessin expeÌrimental eÌquilibreÌ controÌle aÌ la fois le mot-cible (nom vs. verbe) et le contexte qui le preÌceÌde. Les reÌsultats reÌcolteÌs aupreÌs de locuteurs natifs du français queÌbeÌcois ont reÌveÌleÌ un complexe N400-P600 en reÌponse aÌ toutes les anomalies, en contradiction avec les preÌdictions du modeÌle de Friederici. Les effets additifs des manipulations syntaxique et seÌmantique sur la N400 suggeÌrent la deÌtection dâune incoheÌrence entre la racine du mot qui avait eÌteÌ preÌdite et la cible, dâune part, et lâactivation lexico-seÌmantique, dâautre part. Les reÌponses individuelles se sont pas caracteÌriseÌes par une dominance vers la N400 ou la P600: au contraire, une onde biphasique est preÌsente chez la majoriteÌ des participants. Cette activation peut donc eÌtre consideÌreÌe comme un index fiable des meÌcanismes qui sous-tendent le traitement des structures syntagmatiques.
La deuxieÌme eÌtude se concentre sur les meÌme processus chez les apprenants tardifs du français L2. LâhypotheÌse de la convergence (Green, 2003 ; Steinhauer, 2014) preÌdit que les apprenants dâune L2, sâils atteignent un niveau avanceÌ, mettent en place des processus de traitement en ligne similaires aux locuteurs natifs. Cependant, il est difficile de consideÌrer en meÌme temps un grand nombre de facteurs qui se rapportent aÌ leurs compeÌtences linguistiques, aÌ lâexposition aÌ la L2 et aÌ lâaÌge dâacquisition. Cette eÌtude continue dâexplorer les diffeÌrences inter-individuelles en modeÌlisant les donneÌes de potentiels-eÌvoqueÌs avec les ForeÌts aleÌatoires, qui ont reÌveÌleÌ que le pourcentage dâexplosition au français ansi que le niveau de langue sont les preÌdicteurs les plus fiables pour expliquer les reÌponses eÌlectrophysiologiques des participants. Plus ceux-ci sont eÌleveÌs, plus lâamplitude des composantes N400 et P600 augmente, ce qui confirme en partie les preÌdictions faites par lâhypotheÌse de la convergence.
En conclusion, le modeÌle de la âsyntaxe en premierâ nâest pas viable et doit eÌtre remplaceÌ. Nous suggeÌrons un nouveau paradigme baseÌ sur une approche preÌdictive, ouÌ les informations seÌmantiques et syntaxiques sont activeÌes en paralleÌle dans un premier temps, puis inteÌgreÌes via un recrutement de meÌcanismes controÌleÌs. Ces derniers sont modeÌreÌs par les capaciteÌs inter-individuelles refleÌteÌes par lâexposition et la performance.The present thesis uses event-related potentials (ERPs) to investigate neurocognitve mechanisms underlying sentence comprehension. In particular, these two experiments seek to clarify the interplay between syntactic and semantic processes in native speakers and second language learners. Friedericiâs (2002, 2011) âsyntax-firstâ model predicts that syntactic categories are analyzed at the earliest stages of speech perception reflected by the ELAN (Early left anterior negativity), reported for syntactic category violations. Further, syntactic category violations seem to prevent the appearance of N400s (linked to lexical-semantic processing), a phenomenon known as âsemantic blockingâ (Friederici et al., 1999). However, a review article by Steinhauer and Drury (2012) argued that most ELAN studies used flawed designs, where pre-target context differences may have caused ELAN-like artifacts as well as the absence of N400s.
The first study reevaluates syntax-first approaches to sentence processing by implementing a novel paradigm in French that included correct sentences, pure syntactic category violations, lexical-semantic anomalies, and combined anomalies. This balanced design systematically controlled for target word (noun vs. verb) and the context immediately preceding it. Group results from native speakers of Quebec French revealed an N400-P600 complex in response to all anomalous conditions, providing strong evidence against the syntax-first and semantic blocking hypotheses. Additive effects of syntactic category and lexical-semantic anomalies on the N400 may reflect a mismatch detection between a predicted word-stem and the actual target, in parallel with lexical-semantic retrieval. An interactive rather than additive effect on the P600 reveals that the same neurocognitive resources are recruited for syntactic and semantic integration. Analyses of individual data showed that participants did not rely on one single cognitive mechanism reflected by either the N400 or the P600 effect but on both, suggesting that the biphasic N400-P600 ERP wave can indeed be considered to be an index of phrase-structure violation processing in most individuals.
The second study investigates the underlying mechanisms of phrase-structure building in late second language learners of French. The convergence hypothesis (Green, 2003; Steinhauer, 2014) predicts that second language learners can achieve native-like online- processing with sufficient proficiency. However, considering together different factors that relate to proficiency, exposure, and age of acquisition has proven challenging. This study further explores individual data modeling using a Random Forests approach. It revealed that daily usage and proficiency are the most reliable predictors in explaining the ERP responses, with N400 and P600 effects getting larger as these variables increased, partly confirming and extending the convergence hypothesis.
This thesis demonstrates that the âsyntax-firstâ model is not viable and should be replaced. A new account is suggested, based on predictive approaches, where semantic and syntactic information are first used in parallel to facilitate retrieval, and then controlled mechanisms are recruited to analyze sentences at the interface of syntax and semantics. Those mechanisms are mediated by inter-individual abilities reflected by language exposure and performance
ISDN : telematica per tutti?
Abstract not availabl
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