Executive function, the cognitive processes that allow the voluntary control of goal-directed behaviour, can be studied through the examination of inhibition of action. The countermanding paradigm has been shown to be a powerful tool to examine a subject’s ability to withhold responses to a go stimulus when a stop signal is presented occasionally. Logan and Cowan (1984) developed a race model to account for countermanding performance in humans, proposing that independent go and stop process initiated by the go and stop signals respectively, race toward a finish line whereby the first process to cross its finish line determines the behavioural outcome. The model allows estimation of the stop signal response time, a variable that is not directly observable. The race model has yet to be validated for countermanding performance in rats. Using a new rodent countermanding task inspired directly from human studies, male Wistar rats were trained to respond to a visual stimulus (go signal) by pressing a lever below an illuminated light for food reward, but to countermand lever the press (25% of trials) subsequent to an auditory tone (stop signal) presented after a variable delay. The ability to cancel a response decreased as stop signal delay increased. The stop signal response time for rats was estimated to be 157 ms, a value within the range of human estimates. Predictions of countermanding performance made by the race model were generally respected. Response times of movements that escape inhibition: 1) were shorter than those of movements made in the absence of a stop signal; 2) gradually lengthened with increasing stop signal delay; and most importantly, 3) were predicted by the race model. These findings demonstrate that the countermanding performance of rodents can be accounted for by a simple race model, which has been applied successfully in human studies and nonhuman primate models. This new animal model will permit complementary invasive investigations of brain mechanisms underlying inhibitory control and refine the existing rodent models of neurological disease and impulsivity. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2008-09-30 11:35:44.713

Notre travail s’inscrit dans une conception fonctionnaliste de la mémoire qui se donne pour objectif de décrire le fonctionnement de la mémoire plus que sa structure. Notre assise théorique est basée sur le modèle Act-in qui postule que la mémoire est représentée par un ensemble de traces multidimensionnelles. Ces traces comporteraient l’ensemble des dimensions d’une expérience (e.g., motrices, sensorielles, émotionnelles). Pour rendre compte de l’émergence des connaissances, ce modèle repose sur deux mécanismes : l’activation et l’intégration. Notre travail avait pour objectif de spécifier les relations fonctionnelles entre activation et intégration à travers les mécanismes perceptifs et les mécanismes mnésiques. Nous avons également proposé un mécanisme d’interaction, permettant de rendre compte de la formation des traces sensorielles en mémoire. Comme le modèle Act-in conçoit les traces en mémoire comme étant multidimensionnelles, nous avons étudié les différentes relations entre mécanismes d’intégration, interaction et activation via le prisme de la multimodalité. Ce travail s’est organisé autour de deux grands axes expérimentaux, un premier tourné vers l’intégration en perception et l’autre vers l’intégration en mémoire.Dans un premier axe, nous avons introduit la notion d’interaction multimodale pour rendre compte des relations entre modalités sensorielles dans des tâches perceptives. Nous avons montré que lorsque des interactions sensorielles étaient systématiquement répétées, les performances de sujets étaient meilleures que celles observées dans un contexte multimodal dans lequel les modalités sensorielles n’entretenaient pas de lien. Nous avons mesuré à l’aide d’un outil mathématique, le Race Model, le gain multi-sensoriel dans diverses conditions. Nous avons montré que le Race Model mesurait un gain multi-sensoriel essentiellement lorsque la tâche n’impliquait pas de processus mnésiques (i.e., détection). Selon nous, cela montre que cet outil mathématique est plus sensible à l’interaction multimodale, lorsque les composants sensoriels ne sont pas intégrés en mémoire.Dans un second axe, nous avons développé un paradigme expérimental permettant de mesurer les effets d’un encodage sensoriel sur une récupération ultérieure (i.e., catégorisation, reconnaissance et rappel libre). Nous avons montré qu’une association multimodale congruente lors d’un encodage (e.g., image de chien et aboiement du chien) améliorait significativement les performances dans diverses tâches de mémoire. Selon nous, l’activation des dimensions auditives associées au sein de la trace explique cette facilitation lors de la récupération. Nous avons également montré qu’une association multimodale non congruente lors de l’encodage (e.g., image d’un chien et bruit blanc) perturbait la récupération en mémoire à long terme. Ce résultat apporte un argument supplémentaire en faveur des modèles de mémoire qui postulent que les connaissances sont avant tout sensorielles.Pour résumer, ce travail a permis dans un premier temps de proposer un mécanisme d’interaction multimodale nécessaire à l’intégration des composants sensoriels en mémoire. Dans un second temps, nous avons montré que des modalités sensorielles associées lors de l’encodage pouvait être réactivées ultérieurement et faciliter le traitement uniquement si les modalités sensorielles étaient sémantiquement congruentes. Ce résultat renforce la conception d’une mémoire organisée autour de connaissances avant tout sensorielles.Enfin, les résultats que nous obtenons suggèrent que la mémoire et la perception partagent des traitements communs car un trait perceptivement absent peut influencer un trait perceptivement présent et réciproquement. Cela nous permet d’envisager une relation horizontale entre mémoire et perception et remet en question la conception traditionnelle top-down des liens entre mémoire et perception. / Our conception of memory has the aim to describe the memory process more than the memory architecture. Our theoretical approach is based on the Act-in model, postulating that memory is represented by a multidimensional set of traces. These traces should include all dimensions of an experience (e.g., sensory-motor and emotional components). This model relies on two mechanisms (i.e., activation and integration) in order to reveal the emergence of knowledge. The aim of this work was to specify the functional relationships between activation and integration through memory and perception mechanisms. We also proposed a mechanism of interaction, to understand the formation of sensory memory traces. The model Act-in is composed by multidimensional memory traces. Thus, we studied the relationship between integration, interaction and activation through multimodality. This work was organized around two main axis. On one hand perceptual integration and on the other hand the memory integration.In the first axis, we have introduced the concept of multimodal interaction to show the relationship between sensory modalities in perceptual tasks. Our results revealed that when sensory interactions were systematically repeated, the performance of subjects were better than those observed in a context in which multimodal sensory modalities did not maintain a link. We measured using a mathematical tool, the Race Model, multi-sensory gain under various conditions. We have shown that the Race Model measured multi-sensory gain, mainly when the task did not involve memory processes (i.e., detection). This mathematical tool seems to be more sensitive to multimodal interaction, when the sensory components are not integrated into memory.In the second axis, we used an experimental paradigm to measure the effects of sensory encoding on subsequent retrieval tasks (i.e., categorization, recognition and free recall). Our results showed that a congruent multimodal association at encoding (e.g., image of dog and the dog barking) improved performance in various memory tasks. It seems that the activation of the sensory dimensions could explain the facilitation during retrieval. Moreover, an incongruent multimodal association at encoding (e.g., image of a dog and white noise) disturbed performance from retrieval in long-term memory. This result provides a further argument supporting sensory-based memory model.In summary, we propose a multimodal interaction mechanism for the integration of sensory components in memory. Secondly, we have shown that sensory modalities associated during encoding could be reactivated later and facilitate the processing only when the sensory modalities were semantically congruent. This result improves the assumption that memory is sensory-based.Finally, theses results suggest that memory and perception share common features. The reactivation of a sensory dimension can influence the perceptual dimension processing and vice versa. This allows us to consider a horizontal relationship between memory and perception. In such case, the traditional relationship between memory and perception, as assumed to be top-down, could be questioned.

One of the most basic reaction time experiments employed by psychologists is the comparison of latencies to responses for single and redundant targets. The general effect is that participants are capable of responding faster, that is having shorter response latencies when redundant stimuli, as opposed to an individual stimulus, are presented. Interestingly, several models attempting to predict this effect, including the well known race model, have not been entirely successful. The following study evaluated redundancy gain and violations of the race model, in three experimental models: visual only, auditory only, and a visual-auditory bimodal paradigm. The results showed redundancy gain in all three paradigms, but they were only significant violations of the race model for the visual-auditory condition. Additionally, correlations between the different paradigms were explored with respect to redundancy gain and violations of the race model on an individual participant basis.

Master of Science / Department of Journalism and Mass Communications / Joye C. Gordon / The goal of this graduate-level report is to establish a research-based communications plan for the Centralia High School Alumni Association (CHSAA) in order to build permanence in relationships between alumni members and the school, as well as, to secure the financial future of the organization. The project will follow a standard public relations RACE (research, action, communication, and evaluation) model. Background research summarizing current trends in the economy, fundraising, donor motivations and solicitation tactics; CHSAA and the environment that surrounds the organization, the school, and businesses in the communities; intervening publics and primary research is analyzed. As a result of the background analysis, four key publics and corresponding strategies and tactics to reach those publics are identified. A campaign budget is proposed; a two-year time period is shown for implementation of created tactics; and finally, evaluation criteria are listed to provide CHSAA with mechanisms for measuring progress toward the end goal of CHSAA being a permanent fixture for Centralia Schools, its alumni members and surrounding communities.

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