Alternance de tâches concurrente à l’estimation temporelle : parallélisme et partage de ressources

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2013-2014.L’estimation temporelle prospective est la capacité à estimer la durée d’un stimulus alors que celui-ci est présenté. L’estimation du temps prospective (ci-après nommée estimation du temps) est sensible au partage de ressources cognitives. La réalisation d’une tâche concurrente à l’estimation du temps provoque un effet d’interférence qui affecte le processus d’accumulation d’informations temporelles (voir Brown, 1997, 2008, 2010; Block, Hancock, & Zakay, 2010). Des travaux antérieurs ont démontré que l’effet d’interférence est obtenu quand la tâche secondaire à l’estimation temporelle requiert l’implication de ressources attentionnelles (voir par exemple Brown, 1997, Fortin & Massé, 2000) ou encore la manipulation d’information en mémoire à court terme (Barouillet, Bernardin, Portrat, Vergauwe, & Camos, 2007; Fortin, Champagne, & Poirier, 2007; Fortin, Chérif, & Neath, 2005; Fortin & Rousseau, 1998). Outre l’attention et la mémoire, des auteurs se sont intéressés à l’interférence entre des tâches dites exécutives et l’estimation temporelle. Certains auteurs suggèrent en effet que l’estimation temporelle implique des ressources de contrôle exécutif. Brown (2006) rapporte une interférence entre l’estimation du temps et une tâche de génération aléatoire de nombres, une tâche qui impliquerait le contrôle exécutif. Zakay et Block (2004) rapportent un effet similaire avec l’alternance de tâches, un paradigme employé afin d’étudier le contrôle cognitif. Cependant, Fortin, Schweickert, Gaudreault, & Viau-Quesnel (2010) ne trouvent pas d’effet d’alternance avec une tâche d’estimation temporelle concurrente. L’objectif général de la présente thèse est d’étudier l’impact de différentes manipulations au paradigme d’alternance de tâches dans une situation de double tâche avec estimation temporelle. Plus spécifiquement, l’influence de la valence des stimuli, la préparation et le recours à un paradigme d’alternance volontaire sont étudiés. Les présents travaux visent ainsi à mieux définir les processus exécutifs impliqués dans l’estimation de temps et, du même coup, permettront d’apporter un éclairage nouveau en ce qui à trait aux mécanismes qui expliquent le coût d’alternance de tâches, un effet classique mais dont les modèles explicatifs sont encore l'objet d'études et de tests empiriques. Pour ce faire, deux expériences employant un paradigme d’alternance bivalent et permettant la manipulation d’intervalles de préparation (Chapitre II) et trois expériences employant un paradigme d’alternance de tâches volontaire (Chapitre III) sont effectuées. Dans toutes les expériences de la thèse, deux conditions, temps de réaction et production temporelle, permettent de déterminer si le paradigme développé génère des coûts d’alternance en condition de tâche seule (condition temps de réaction) et en condition de double tâche concurrente à une tâche de production d’intervalle temporel (condition production temporelle). De plus, une manipulation de la charge en mémoire entre les essais permet de comparer l’effet d’alternance à celui de la recherche en mémoire, un effet qui devrait théoriquement interférer avec l’estimation temporelle concurrente (Fortin, Champagne, & Poirier, 2006). Les résultats des expériences du Chapitre II montrent que l’alternance de tâches bivalente génère des coûts d’alternance en situation de tâche seule et que ces coûts d’alternance diminuent asymptotiquement avec la préparation. Cependant, dans la condition avec production temporelle, l’effet d’alternance n’est pas obtenu, suggérant que l’alternance avec des stimuli bivalents n’interfère pas avec l’estimation temporelle. De plus, la manipulation de l’intervalle indice-cible, qui permet la préparation, n’est pas associée avec une augmentation des productions temporelles, mais, au contraire, avec une diminution de la sous-estimation du temps qui passe, c’est-à-dire une amélioration de la performance à l’estimation du temps pendant l’intervalle de préparation. Les résultats du Chapitre II suggèrent donc que l’alternance de tâches et l’estimation temporelle ne partagent pas de ressources cognitives. Le Chapitre III s’intéresse à un paradigme novateur dans le domaine de l’alternance de tâches : le paradigme d’alternance volontaire. Développé par Arrington et Logan (2004; 2005), ce paradigme a pour objectif de forcer l’implication de contrôle descendant en retirant les indices qui identifient la tâche à effectuer par le participant. Dans ce paradigme, les consignes au participant sont d’alterner approximativement une fois sur deux et au hasard. Les résultats du Chapitre III démontrent que le paradigme d’alternance volontaire génère des coûts d’alternance tant dans la condition de tâche seule que dans la condition de double tâche avec l’estimation temporelle. Ces résultats suggèrent d’une part que l’alternance volontaire se distingue de l’alternance involontaire et, de plus, suggèrent que l’alternance volontaire sollicite des ressources cognitives qui sont également impliquées dans l’estimation temporelle. Il appert donc que l’estimation du temps dépend de ressources dites exécutives, mais que ces ressources ne sont pas unitaires ni homogènes. Spécifiquement, les présents travaux permettent de postuler que les ressources de contrôle descendant soient impliquées dans l’estimation temporelle, mais pas les processus de contrôle ascendant qui émergent des indices contextuels.Prospective timing is the capacity to estimate the duration of a stimulus as it is presented. Prospective timing (hereafter referred to as timing) is sensitive to resource-sharing. In dual task paradigms, timing performance diminishes when resources involved in timing are also involved in the secondary task (interference effect, see Brown, 1997, 2008, 2010; Block, Hancock, & Zakay, 2010). Previous work has shown that an interference effect is obtained when timing is done concurrently with a task which requires the involvement of attentional resources (e.g. Brown, 1997, Fortin & Massé, 2000) or the manipulation of information in short term memory (Barouillet, Bernardin, Portrat, Vergauwe, & Camos, 2007; Fortin, Champagne, & Poirier, 2007; Fortin, Chérif, & Neath, 2005; Fortin & Rousseau, 1998). Apart from attentional and memory resources, authors have studied the interference effect with executive tasks. Some authors suggest that timing involves executive resources. Brown (2006) found an interference effect between timing and a random number generation task, a task which involves executive control. Zakay and Block (2004) observed a similar effect in a dual task experiment with timing and concurrent task switching, a paradigm often used to study cognitive control (see Monsell, 2003, for a concise review). However, Fortin, Schweickert, Gaudreault and Viau-Quesnel (2010) found no interference between task switching and concurrent timing, using a local measure of switch costs. The general objective of this thesis is to study the impact of manipulations and variations of the task switching paradigm in a dual task condition with concurrent timing. Specifically, stimuli valence, preparation and voluntary task switching are studied. The present thesis aims to better define executive processes involved in timing and, at the same time, shed new light on the nature of the processes which account for the task switch cost, a robust effect for which explanatory models remain uncertain. To this end, two experiments manipulating stimuli valence and preparatory intervals (see Chapitre II) and three experiments using a voluntary task switching paradigm (see Chapitre III) were run. In all experiments of the thesis, two conditions, reaction time and time production, allow to determine if the task switching paradigm generates switch costs in a single task condition (reaction time condition) and in a dual task condition with concurrent timing (time production condition). Also, a manipulation of memory load between trials allows comparing the effects of task switching and of memory load, the latter having been shown to interfere with concurrent timing in previous research (Fortin, Champagne, & Poirier, 2006). Results in the first article of the thesis show that bivalent task switching causes switch costs in a single task condition and that switch costs diminished asymptotically with preparation. However, in the time production condition, the effect of task switching is not significant, suggesting that task switching with bivalent stimuli does not interfere with concurrent timing. Furthermore, a manipulation of the cue-stimulus interval, which allows for preparation to task switches, did not interfere with concurrent timing. To the contrary, longer cue-stimulus intervals led to reduced over-productions of time intervals, meaning that performance in the timing task improved with longer cue-stimulus intervals. Results in the first article of the thesis suggest that timing and task switching do not share cognitive resources. In the second article of the thesis, voluntary task switching is studied. The voluntary task switching paradigm was developed by Arrington and Logan (2004; 2005) and had for objective to ensure that participants had to engage top-down cognitive control resources. This was done by removing task identifying cues and replacing them by instructions which asked participants to switch tasks randomly on approximately half trials. Results in the second article show that voluntary task switching led to switch costs in both the single task (reaction time) and dual task (time production) conditions. These results suggest that voluntary task switching engages different cognitive resources than cued task switching. Results also imply that voluntary task switching elicits resources which are required in timing. It therefore seems that timing requires executive resources, but not bottom-up processes which are involved in cued task switching

T1000: a reduced gene set prioritized for toxicogenomic studies

There is growing interest within regulatory agencies and toxicological research communities to develop, test, and apply new approaches, such as toxicogenomics, to more efficiently evaluate chemical hazards. Given the complexity of analyzing thousands of genes simultaneously, there is a need to identify reduced gene sets. Though several gene sets have been defined for toxicological applications, few of these were purposefully derived using toxicogenomics data. Here, we developed and applied a systematic approach to identify 1,000 genes (called Toxicogenomics-1000 or T1000) highly responsive to chemical exposures. First, a co-expression network of 11,210 genes was built by leveraging microarray data from the Open TG-GATEs program. This network was then re-weighted based on prior knowledge of their biological (KEGG, MSigDB) and toxicological (CTD) relevance. Finally, weighted correlation network analysis was applied to identify 258 gene clusters. T1000 was defined by selecting genes from each cluster that were most associated with outcome measures. For model evaluation, we compared the performance of T1000 to that of other gene sets (L1000, S1500, Genes selected by Limma, and random set) using two external datasets based on the rat model. Additionally, a smaller (T384) and a larger version (T1500) of T1000 were used for dose-response modeling to test the effect of gene set size. Our findings demonstrated that the T1000 gene set is predictive of apical outcomes across a range of conditions (e.g., in vitro and in vivo, dose-response, multiple species, tissues, and chemicals), and generally performs as well, or better than other gene sets available

Ascaris suum informs extrasynaptic volume transmission in nematodes

Neural circuit synaptic connectivities (the connectome) provide the anatomical foundation for our understanding of nematode nervous system function. However, other nonsynaptic routes of communication are known in invertebrates including extrasynaptic volume transmission (EVT), which enables short- and/or long-range communication in the absence of synaptic connections. Although EVT has been highlighted as a facet o

Sources, concentrations, and risks of naphthalene in indoor and outdoor air

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92148/1/j.1600-0668.2011.00760.x.pd

The seeds of divergence: the economy of French North America, 1688 to 1760

Generally, Canada has been ignored in the literature on the colonial origins of divergence with most of the attention going to the United States. Late nineteenth century estimates of income per capita show that Canada was relatively poorer than the United States and that within Canada, the French and Catholic population of Quebec was considerably poorer. Was this gap long standing? Some evidence has been advanced for earlier periods, but it is quite limited and not well-suited for comparison with other societies. This thesis aims to contribute both to Canadian economic history and to comparative work on inequality across nations during the early modern period. With the use of novel prices and wages from Quebec—which was then the largest settlement in Canada and under French rule—a price index, a series of real wages and a measurement of Gross Domestic Product (GDP) are constructed. They are used to shed light both on the course of economic development until the French were defeated by the British in 1760 and on standards of living in that colony relative to the mother country, France, as well as the American colonies. The work is divided into three components. The first component relates to the construction of a price index. The absence of such an index has been a thorn in the side of Canadian historians as it has limited the ability of historians to obtain real values of wages, output and living standards. This index shows that prices did not follow any trend and remained at a stable level. However, there were episodes of wide swings—mostly due to wars and the monetary experiment of playing card money. The creation of this index lays the foundation of the next component. The second component constructs a standardized real wage series in the form of welfare ratios (a consumption basket divided by nominal wage rate multiplied by length of work year) to compare Canada with France, England and Colonial America. Two measures are derived. The first relies on a “bare bones” definition of consumption with a large share of land-intensive goods. This measure indicates that Canada was poorer than England and Colonial America and not appreciably richer than France. However, this measure overestimates the relative position of Canada to the Old World because of the strong presence of land-intensive goods. A second measure is created using a “respectable” definition of consumption in which the basket includes a larger share of manufactured goods and capital-intensive goods. This second basket better reflects differences in living standards since the abundance of land in Canada (and Colonial America) made it easy to achieve bare subsistence, but the scarcity of capital and skilled labor made the consumption of luxuries and manufactured goods (clothing, lighting, imported goods) highly expensive. With this measure, the advantage of New France over France evaporates and turns slightly negative. In comparison with Britain and Colonial America, the gap widens appreciably. This element is the most important for future research. By showing a reversal because of a shift to a different type of basket, it shows that Old World and New World comparisons are very sensitive to how we measure the cost of living. Furthermore, there are no sustained improvements in living standards over the period regardless of the measure used. Gaps in living standards observed later in the nineteenth century existed as far back as the seventeenth century. In a wider American perspective that includes the Spanish colonies, Canada fares better. The third component computes a new series for Gross Domestic Product (GDP). This is to avoid problems associated with using real wages in the form of welfare ratios which assume a constant labor supply. This assumption is hard to defend in the case of Colonial Canada as there were many signs of increasing industriousness during the eighteenth and nineteenth centuries. The GDP series suggest no long-run trend in living standards (from 1688 to circa 1765). The long peace era of 1713 to 1740 was marked by modest economic growth which offset a steady decline that had started in 1688, but by 1760 (as a result of constant warfare) living standards had sunk below their 1688 levels. These developments are accompanied by observations that suggest that other indicators of living standard declined. The flat-lining of incomes is accompanied by substantial increases in the amount of time worked, rising mortality and rising infant mortality. In addition, comparisons of incomes with the American colonies confirm the results obtained with wages— Canada was considerably poorer. At the end, a long conclusion is provides an exploratory discussion of why Canada would have diverged early on. In structural terms, it is argued that the French colony was plagued by the problem of a small population which prohibited the existence of scale effects. In combination with the fact that it was dispersed throughout the territory, the small population of New France limited the scope for specialization and economies of scale. However, this problem was in part created, and in part aggravated, by institutional factors like seigneurial tenure. The colonial origins of French America’s divergence from the rest of North America are thus partly institutional

PmrAB-regulated LPS phosphoethanolamine modifications have multiple roles in «Citrobacter rodentium»

Gram-negative bacteria have the ability to modify their lipopolysaccharide (LPS) in response to changing environmental conditions. The principal regulator of LPS modifications in the Enterobacteriaceae is the PmrA-PmrB (PmrAB) two-component system, which is activated by micromolar concentrations of Fe3+ and Al3+ and mildly acidic pH. PmrAB mediates the transcription of pmrC and cptA, encoding phosphoethanolamine (pEtN) transferases that catalyze the addition of pEtN to the 1- and 4’-phosphoryl groups of the lipid A moiety and to the phosphoryl group of heptose-I of the core moiety of LPS, respectively. The first objective was to determine if PmrC- and CptA-mediated pEtN modifications play a role in maintaining outer membrane integrity in C. rodentium under PmrAB-inducing conditions. To assess the role of pEtN modifications in outer membrane integrity, C. rodentium ∆pmrAB, ∆pmrC, ∆cptA and ∆pmrC∆cptA strains were generated. The ∆pmrC, ∆pmrC∆cptA and ∆pmrAB demonstrated increased susceptibility to hydrophobic antibiotics, whereas only the ∆pmrC∆cptA and ∆pmrAB strains displayed a loss of OM integrity under PmrAB-inducing conditions. The second objective was to determine the mechanism by which PmrC- and CptA-mediated pEtN modifications maintain outer membrane integrity under PmrAB-inducing conditions. Whole-cell lysate LPS extractions performed on ∆waaL strains grown in the presence of micromolar concentrations of iron demonstrated that the ∆waaL∆pmrC∆cptA strain accumulates free lipid A, which is a measure of a defect in LPS turnover. Using sucrose density gradient centrifugation, it was shown that the ∆waaL∆pmrC∆cptA strain accumulated LPS throughout its cell envelope in the presence of micromolar iron, whereas the ∆waaL strain had most of its LPS in the fractions corresponding to the outer membrane, suggesting that pEtN modifications are involved in the transfer of LPS from the IM to the OM. The third objective was to determine whether the response to iron results in the formation of OM vesicles (OMVs). It was determined that OM vesiculation does occur in the presence of 50 to 100 µM FeSO4, confirmed by the presence of CroP, an OM protease. In addition, the isolated OMVs were shown to be more bactericidal against the ∆waaL∆pmrC∆cptA strain than the ∆waaL strain, suggesting that PmrC and CptA are involved in conferring protection against these OMVs.Les bactéries à Gram négatif peuvent modifier la couche externe de lipopolysaccharide (LPS) pour s’adapter au changement des conditions environnementales. Le principal régulateur des modifications du LPS chez les entérobactéries est le système à deux composants PmrA-PmrB (PmrAB), qui est activé par des concentrations de Fe3+ et d’Al3+ de l’ordre du micromolaire, ainsi que par un pH acide. PmrAB induit la transcription des gènes pmrC et cptA, qui codent pour des transférases de phosphoéthanolamine (pEtN) et catalysent l’addition de pEtN aux groupes 1-, 4’-phosphoryl du lipide A et au groupe phosphoryl du résidu heptose-I du noyau. Le premier objectif est de déterminer si les modifications du LPS induites par PmrC et CptA jouent un rôle dans le maintien l’intégrité de la membrane externe chez C. rodentium, dans des conditions qui activent PmrAB. Pour ce faire, les souches de C. rodentium ΔpmrAB, ΔpmrC, ΔcptA et ΔpmrCΔcptA ont été générées. Les souches ΔpmrC, ΔpmrCΔcptA et ΔpmrAB ont démontré une susceptibilité accrue aux antibiotiques hydrophobes, par contre seules les souches ΔpmrCΔcptA et ΔpmrAB ont perdu l’intégrité de leur membrane externe. Le deuxième objectif est de déterminer le mécanisme moléculaire par lequel les modifications du LPS induites par PmrC et CptA maintiennent l’intégrité de la membrane externe dans des conditions qui activent PmrAB. Des extractions de LPS ont été réalisées à partir de lysats cellulaires de souches ΔwaaL produisant un LPS tronqué, afin de pouvoir observer spécifiquement la production de LPS constitué du lipide A et du noyau. Les résultats ont démontré que la souche ΔwaaLΔpmrCΔcptA accumule du lipide A non lié au noyau. En employant la centrifugation sur gradient de sucrose suivie d’un buvardage de type Western contre le KDO, nous avons montré que la souche ΔwaaLΔpmrCΔcptA accumule le LPS tout au long de son enveloppe cellulaire, tandis que la souche ΔwaaL transfert la majorité de son LPS vers la membrane externe. Ceci démontre que les modifications du LPS induites par PmrC et CptA aident au transfert du LPS de la membrane interne vers la membrane externe. Le troisième objectif est de déterminer si la présence du fer induit la formation de vésicules à la membrane externe. En mesurant la présence de CroP, une protéase de la membrane externe, à la surface de vésicules isolées, nous avons montré que des concentrations de fer de l’ordre de 50 à 100 μM induisent la formation de vésicules. De plus, ces vésicules exercent un effet bactéricide plus important contre la souche ΔwaaLΔpmrCΔcptA que contre la souche ΔwaaL, suggérant que PmrC et CptA confèrent aux bactéries C. rodentium une protection contre les vésicules produites

Michèle Héon

Through notions of time, death and ruin, Charles establishes links between Héon's "robes," the sacrificial cloak of Heracles, and the kimono as uniform. Viau compares the artist's deployment of oversized and minuscule objects to Bachelard's dream-space (text in French only). Pringle discusses material surfaces, archetypal content and the reversibility inherent in Héon's textile art. Biographical notes. 10 bibl. ref