No description available.

No description available.

No description available.

Pas de résumé / In this thesis, we developed a new experimental paradigm for studying how recent sensory history (the context) affects a basic aspect of auditory perception, the comparison of successive frequency components. Stimuli were devised to include ambiguous transitions between frequency components, as it was hypothesized that such an ambiguity would make the task especially prone to reveal context effects. Six psychophysical experiments are reported. Using pairs of Shepard tones (Shepard, J. Acoust. Soc. Am., 1964), we first demonstrate a strong hysteresis effect when successive pairs are judged, whereby past trials affect current judgments. We then isolate the cause of this context effect, by contrasting perceptual reports for a same ambiguous test pair when preceded by different contexts. We show that frequency shifts are preferentially reported when they encompass a frequency regions that was stimulated during the context. This context effect is rapidly introduced, as a single tone as short as 20ms can produce a reliable bias. Yet it also has an enduring effect on perception, persisting over more than 30s. Using random chords pairs designed to include ambiguous frequency shifts, it then shown that the context effect is not specific to Shepard tones but rather reflects a generic process acting on the tonotopic representation of sounds. Finally, the context effect is modulated by both low-level (ear-of-entry) and high-level (selective attention) manipulations, suggesting an interplay between several processing stages for the underlying neural mechanism. Our findings show that one of the most ubiquitous and basic tasks of the auditory system, comparing successive frequency components, is not a fixed function of the physical stimulus. Rather, it is highly malleable and depends on the ongoing context.

Thesis: S.B. in Chemistry-Biology, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2018. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged student-submitted from PDF version of thesis. "Submitted to the Department of Brian and Cognitive Sciences in supplement to the requirements for the degree of Bachelor of Science in Chemistry-Biology." / Includes bibliographical references (pages 52-54). / X-linked dystonia parkinsonism (XDP), also known as torsion dystonia type 3 (DYT3), afflicts hundreds of individuals. Under an X-linked mode of inheritance, the DYT3 haplotype occurs in Filipino populations and is of the highest frequency in the Panay Islands of the Philippines. Recently, convincing evidence has shown the causative mutation to be an insertion of the repetitive sequence SINE-VNTR-Alus (SVA). This insertion is associated with misregulation of 3' end exons in the gene TBP-associated factor 1 (TAF1). TAF1, the largest of fourteen TAF proteins, incorporates into a TATA binding complex that promotes transcription by RNA polymerase II. In a collaborative effort, singleplex BaseScope" probes as well as antibodies have been produced to target two TAF1 isoforms, canonical TAF1, C-TAF1, and neuronal TAF1, N-TAF1, separately. N-TAF1 differs from C-TAF1 by the inclusion of a two amino acid microexon, 3' to the SVA insertion, known as 34'. Here, I show that N-TAF1 expression is confined to neurons and interneurons whereas C-TAF1 is widely expressed, particularly by astrocytes, interneurons, neurons, and cells present in other organs including the heart and liver in mouse. Additionally, the antibodies produced show promise for use in human tissue. These results support the hypothesis that C-TAF1 and N-TAF1 have canonical and neuron-specific functions, respectively, and misregulation of N-TAF1 is capable of causing neuronal degeneration. Ultimately these results set the foundation for the study of C-TAF1 and N-TAF1 functions and isoform misregulation in XDP diseased tissue. Furthermore, these probes and antibodies may serve as tools for the validation of XDP models, under development, in which forthcoming XDP therapies may be tested. / by Mercedes Maye Ondik. / S.B. in Chemistry-Biology

Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Political Science; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 81-86). / State failure is becoming increasingly prevalent across the globe, creating human suffering, black markets, lost economic opportunities, and safe havens for militant actors. It is imperative that the international community find a way to combat state failure. This study investigates the effects of irregular leadership transitions on state failure recovery. Irregular leadership transitions occur when the executive of a state comes to power through unconstitutional means. Regular leaders are more likely than irregular leaders to have personal experience as a ruler, beneficial domestic and international ties, and familiarity among the population. Irregular transitions may damage bureaucracies, damaging government functionality and halting development projects that had already been underway. Regular leaders benefit from a legacy that was likely able to pass spoils onto an elite group. This elite group is likely to resist relative losses to power more than lower status groups would fight to gain power because of the cognitive principles of risk aversion, and the sensitivity to status inherent to social identity theory. Regular leaders also have traditional legitimacy, while irregular leaders are more likely to have to gain legitimacy. State failure and failure recovery are overdetermined, so it is impossible to be able to confidently determine the direction of causal flow. Every determinant of failure is related to every other, and it is difficult to separate their effects. The role of leadership regularity is therefore investigated as a proxy that can predict variation on the rate of failure recovery. The quantitative analysis consisted of multi and bivariate regressions investigating the effects of leadership regularity on failure duration, as well as the relative explanatory power held by several factors associated with leadership regularity. Robustness checks were performed using Bayesian statistics, and survival analyses. Irregular leadership transitions were found to predict a roughly five year increase in state failure duration. The Afghan Civil War was used as an illustrative case, describing the ways in which Daoud, Taraki, Amin, Karmal, Massoud, Hekmatyar, and Mullah Omar all overcame, or failed to overcome, different obstacles associated with their irregularity and how these obstacles affected their relative levels of success attempting to extend governance. / by Laila A. Wahedi. / S.B. / S.M.and S.B.

No description available.

No description available.

Le cortex visuel ventral chez l’homme se compose d’une mosaïque de régions spécialisées dans la reconnaissance de différentes catégories d’objets. Selon une organisation reproductible, certaines régions répondent préférentiellement aux visages, alors que d’autres sont plus activées par les maisons et les lieux, par les outils, ou encore par les parties du corps. Plusieurs facteurs ont été invoqués pour expliquer la préférence d’une région pour une catégorie donnée, tels que des biais pour le traitement de certaines caractéristiques visuelles (préférence pour la position fovéale ou périphérique des stimuli, pour leur fréquence spatiale haute ou basse), le degré d’exposition et d’expertise (expertise pour les voitures par exemple), ou la connectivité anatomique vers des réseaux cérébraux spécialisés dans le traitement d’un domaine particulier. Chez les enfants, l’apprentissage de la lecture de mots ou d’autres systèmes symboliques culturels provoque le développement de régions corticales dédiées, telles que l’aire de la forme visuelle des mots (VWFA), au sein d’une voie ventrale en partie déjà stabilisée. Ce développement ontologique tardif pour la reconnaissance de symboles, indépendamment de contraintes phylogénétiques propres à la lecture, facilite l’étude de ce qui façonne la spécialisation fonctionnelle au sein de la voie ventrale. Dans cette thèse, nous avons étudié la représentation des mots et des partitions de musique au sein du cortex visuel ventral en combinant des méthodes d’imagerie par résonance magnétique fonctionnelle et de diffusion, à des taches comportementales. D’abord, nous montrons que la localisation de la VWFA chez les adultes correspond, en comparaison à des régions voisines du cortex ventral, à une région connectée de manière optimale à celles du langage qui traitent le contenu sémantique et phonologique. Ensuite, nous montrons que les régions ventrales qui sous-tendent le décodage orthographique sont fonctionnellement hétérogènes selon un axe latero-médial. Les régions médianes semblent encoder les graphèmes de façon sérielle, sous le contrôle de régions pariétales, pour les convertir en phonèmes. A l’inverse, les régions latérales traitent les mots de façon plus flexible pour accéder au lexique. Ces études mettent en évidence le rôle majeur de la connectivité anatomique dans le développement d’une spécialisation fonctionnelle pour les mots, avec la contribution de connectivités diverses qui participent à l’hétérogénéité fonctionnelle du système de la forme visuelle des mots. Enfin, nous observons que la maîtrise de la lecture musicale a d’importantes conséquences sur la latéralisation ventrale d’autres catégories. D’une part, la latéralisation à gauche augmente dans des régions latérales ventrales pour toutes les catégories. D’autre part, la latéralisation à droite augmente dans des régions fusiformes postérieures, notamment pour le traitement des visages et des maisons. Ces conséquences, similaires à celles provoquées par l’apprentissage de la lecture de mots, révèlent des processus à la fois de compétition et de transfert entre catégories. Ainsi, nos résultats suggèrent que des mécanismes communs pourraient expliquer comment une expertise culturelle peut recycler et modifier le cortex visuel. / The human ventral visual cortex hosts a mosaic of areas specialized in the recognition of different categories of objects. According to a reproducible pattern, some areas respond preferentially to faces, while others are more activated by places and buildings, by tools, or by body parts. Several factors have been proposed as major determinants of the preferred category of a given region, such as visual feature biases (preference for peripheral vs. foveal stimuli, or for high vs. low spatial frequencies), experience (e.g., car expertise) and white-matter connectivity to domain-specific brain networks. In children, learning to read words and other cultural symbols triggers the emergence of dedicated cortical areas, such as the visual word form area (VWFA), within a partially settled ventral pathway. This late ontological development for symbol recognition, free from reading-specific evolutionary constraints, facilitates the investigation of what shapes functional specialization in the ventral pathway. In the current work, we studied in particular the representation of words and musical scores in the ventral visual cortex, using functional magnetic resonance imaging (fMRI), diffusion-weighted imaging and behavioral tasks. First, we show that the location of the VWFA in adults corresponds to a region optimally connected to language regions supporting semantics and phonology, as compared to adjacent ventral cortex regions. Second, we demonstrate that ventral regions supporting orthographic decoding are heterogeneous along a medial-to-lateral axis. Medial regions seem to encode graphemes serially for phonological decoding, under the control of parietal regions. In contrast, lateral regions process words more flexibly for lexical access. These studies reveal a major role of white-matter connectivity in shaping functional specialization for words, with differential connections participating in the functional heterogeneity of the VWFA. Third, we observe that musical literacy has a large impact on lateralization patterns in the ventral stream. A domain general enhancement of leftward lateralization takes place in lateral ventral regions, together with a rightward shift in fusiform regions notably for the processing of faces and houses. These consequences probably reflect both competition between visual categories and transfer across them, and resemble the impact of reading acquisition. Together, our results show that common processes may explain how cultural expertise recycles and modifies the visual cortex.

Thèse de doctorat : Sciences cognitives. Psychologie cognitive : Lyon 2 : 2001. / Bibliogr.