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Il apparaît, suite aux résultats de plusieurs études comportementales et d’imagerie cérébrale, que les hormones gonadiques peuvent moduler le fonctionnement cérébral chez la femme. Les asymétries cérébrales fonctionnelles (ACFs), en particulier, changeraient en fonction du niveau de progestérone et d’œstrogène. On a également observé que lorsque le taux d’œstrogène est bas, les performances aux tâches impliquant l’hémisphère droit sont améliorées. Par contre, les preuves de l’action physiologique de ces deux hormones sur le cerveau ne sont pas très nombreuses. Le peu d’études d’électrophysiologie cognitive qui ont porté sur les effets du cycle menstruel ont rapporté que la composante P300 y serait sensible. Aucune n’a cependant utilisé une tâche d’habileté spatiale ou de rotation mentale qui sont connues pour impliquer davantage l’hémisphère droit. Le but de la présente étude est de documenter les changements électrocorticaux reliés aux variations hormonales lors d’une tâche de rotation mentale. Notre hypothèse de départ est que le taux d’œstrogène influencera l’activité électrocorticale et la latéralisation. Les potentiels évoqués cognitifs ont été comparés chez les mêmes femmes (n=12) lors d’une tâche de rotation mentale, répétée à deux périodes du cycle menstruel. Nos résultats démontrent que la condition de rotation induit une latéralisation de l’activité pariétale, vers l’hémisphère gauche, quand le niveau d’œstrogène est bas. Par contre, lorsque le niveau d’œstrogène est élevé, il n’y a aucune latéralisation. Par ailleurs, nous avons observé une augmentation de l’amplitude de la P300 lors du niveau oestrogénique élevé. En conclusion, les fluctuations oestrogéniques du cycle menstruel ont un impact sur la latéralisation de l’activité électrocorticale, lors d’un effort de rotation mentale. / After many behavioral and some neuroimaging studies, it appears that the gonadic hormones can modulate the neuronal function of women's brain. In particular, the functional cerebral asymmetries can be affected by the level of progesterone and estrogens. It has been observed that when the level of estrogen is low, the performance at task that engages more the right hemisphere is enhanced. However, there is a lack of evidence for the physiological actions of these two hormones on the brain. The few event-related potential studies taking into account the menstrual cycle effects, had noticed that the component P300 can be affected. No electrophysiological study has used a mental rotation task or spatial ability tests which are known for their right hemisphere dominance. The aim of the present research is to document the effect of hormonal variations on the electrocortical activity, using a mental rotation task. Our hypothesis is that estrogen levels affect electrocortical activity and lateralization. The ERPs were compared in the same women (n = 12) during a mental rotation task, repeated over two periods of the menstrual cycle. Our results show a lateralization of the left parietal activity when estrogen levels are low and during the rotation. Whereas when the estrogen level is high, there is no lateralization. In addition, we observed an increase in the amplitude of P300 for this same high level. In conclusion, estrogens fluctuations associated with the menstrual cycle have an impact on the lateralization of electrocortical activity, when a mental rotation is needed.

Empathische Reaktionen auf emotionale Gesichtsausdrücke werden vom Alter beeinflusst. In Bezug auf die kognitive Komponente der Empathie wurde eine Einschränkung bei der Erkennung emotionaler Gesichtsausdrücke sowohl für ältere Beobachter als auch für ältere Gesichter berichtet. Manche Studien berichten auch einen Effekt der Alterskongruenz, d.h. eine bessere Erkennung von Emotionen bei der eigenen Altersgruppe. Das erste Ziel der vorliegenden Dissertation war es, Mechanismen, die diesen Effekten zugrunde liegen könnten, zu untersuchen. Das zweite Ziel war es, zu untersuchen, ob auch die affektive Komponente der Empathie vom Alter beeinflusst wird. Studie 1 gibt einen Überblick über frühere Forschungsarbeiten. Studie 2 beschäftigte sich mit der Rolle von altersbezogenen Antwortverzerrungen, d.h. Altersunterschieden bei der Attribuierung bestimmter Emotionen. Effekte des Alters der Beobachter und der Gesichter auf die Erkennung von Trauer waren auf Antwortverzerrungen zurückzuführen. Allerdings trat eine bessere Erkennung von Trauer bei der eigenen Altersgruppe auf, die unabhängig von Antwortverzerrungen war. Studie 3 untersuchte neuronale Prozesse, die diesem Effekt der Alterskongruenz zugrunde liegen könnten. Bei traurigen Gesichtern wurde ein Effekt der Alterskongruenz für späte Verarbeitungsstadien gefunden, der möglicherweise eine höhere Relevanz trauriger Gesichter der eigenen Altersgruppe widerspiegelt. Studie 4 untersuchte, ob auch affektive Reaktionen, gemessen mit Gesichtsmimikry, vom Alter beeinflusst werden. Ältere Beobachter zeigten eine Beeinträchtigung in der Emotionserkennung, nicht jedoch in den affektiven Reaktionen. Insgesamt weisen diese Ergebnisse auf altersbezogene Defizite bei kognitiven und neuronalen Reaktionen hin; allerdings gab es kaum Alterseffekte auf affektive Reaktionen. Also lassen die Ergebnisse insgesamt trotz Schwierigkeiten bei der Emotionserkennung Optimismus bezüglich der intergenerationalen Empathie zu. / Empathic reactions to emotional facial expressions differ according to age. Concerning the cognitive component of empathy, decoding of emotional facial expressions was reported to be impaired both for older observers and older faces. Some studies also reported an own-age advantage, i.e., higher decoding accuracy for the own compared with other age groups. The first aim of the present dissertation was to explore possible mechanisms underlying these age effects. The second aim was to explore whether the affective component of empathy is affected by age as well. Study 1 summarizes previous research. Study 2 explored the role of age-related response bias, that is, age differences in the attribution of specific emotions. It showed that effects of the observers'' and the faces'' ages on decoding sadness were due to age-related response bias. However, an own-age advantage on decoding sadness occurred, which was independent of response bias. Study 3 explored the neurofunctional processes underlying this own-age advantage. It revealed an own-age effect on late processing stages for sadness, which may be due to an enhanced relevance of sad own-age faces. Study 4 explored whether affective responding in terms of facial mimicry is affected by age as well. It revealed an age-related decline in decoding accuracy, but not in affective responding. Taken together, these results suggest age-related deficits in cognitive and neural responses to emotional facial expressions. However, age had little influence on affective responding. Thus, despite difficulties in emotion decoding, these results allow for some optimism regarding intergenerational empathy.

Une interface cerveau-ordinateur permet d'interagir avec un système, comme un système d'écriture, uniquement par l'activité cérébrale. Un des phénomènes neurophysiologiques permettant cette interaction est le potentiel évoqué cognitif P300, lequel correspond à une modification du signal 300 ms après la présentation d'une information attendue. Cette petite réaction cérébrale est difficile à observer par électroencéphalographie car le signal est bruité. Dans cette thèse, de nouvelles techniques basées sur la théorie des ondelettes sont développées pour améliorer la détection des P300 en utilisant des mesures de similarité entre les canaux électroencéphalographiques. Une technique présentée dans cette thèse débruite les signaux en considérant simultanément la phase des signaux. Nous avons également étendu cette approche pour étudier la localisation du P300 dans le but de sélectionner automatiquement la fenêtre temporelle à étudier et faciliter la détection / Brain-Computer Interfaces (BCI) are control and communication systems which were initially developed for people with disabilities. The idea behind BCI is to translate the brain activity into commands for a computer application or other devices, such as a spelling system. The most popular technique to record brain signals is the electroencephalography (EEG), from which Event-Related Potentials (ERPs) can be detected and used in BCI systems. Despite the BCI popularity, it is generally difficult to work with brain signals, because the recordings contains also noise and artifacts, and because the brain components amplitudes are very small compared to the whole ongoing EEG activity. This thesis presents new techniques based on wavelet theory to improve BCI systems using signals' similarity. The first one denoises the signals in the wavelet domain simultaneously. The second one combines the information provided by the signals to localize the ERP in time by removing useless information

Verhaltensstudien haben gezeigt, dass dynamische besser als statische Emotionsausdrücke erkannt werden. Im Einklang mit dieser dynamischer Vorteil Hypothese, haben fMRT Studien eine erhöhte und ausgedehnte Aktivierung für dynamische Emotionsausdrücke gezeigt. Die vorliegende Dissertation hatte das Ziel, die kognitiven Mechanismen, die den dynamischen Vorteil bedingen, zu klären, beziehungsweise die Spezifität dessen Wirkung für Gesichtsausdrücke der sechs Basisemotionen zu untersuchen. Studie 1 verglich Verhaltensdaten und kortikale Reaktionen zwischen dynamischen und statischen Emotionsausdrücken. Studie 2 behandelte methodischen Fragen des Timings der Stimuli und der neutralen dynamischen Bedingung. Studie 3 überprüfte die Hypothese, dass die Erhöhung der Menge von Bewegungen in den Gesichtsausdrücken die Zuweisung der Aufmerksamkeit erhöhen würde, und verglich die Wirkung in emotionalen und nicht-emotionalen Bewegungen. Study 4 konzentrierte sich auf die Frage der Emotionsspezifität der Hirnaktivierung in der Erkennung von Emotionen. Die Ergebnisse bestätigten einen dynamischen Vorteil in der Klassifizierung von Emotionsausdrücken, vermutlich bedingt durch eine Erhöhung in der visuellen Aufmerksamkeit, und eine Verbesserung der Wahrnehmungsverarbeitung. Außerdem, erhöht sich dieser Effekt mit allmählichem Erhöhen der Stärke der Bewegung in beide emotionalen und neutralen Bedingungen. Solche Effekte sprechen für ein perzeptuellen Bias erhöhte Aufmerksamkeit emotionalen verglichen mit neutralen und dynamischen verglichen mit statischen Gesichtern zuzuweisen. Dieser Effekt war für Freude etwas erhöht und für Überraschung reduziert, aber insgesamt ähnlich für alle Emotionsausdrücken. / Behavioral studies have shown that facial expressions of emotion unfolding over time provide some type of information that benefits the recognition of emotional expressions, in comparison with static images. In line with the dynamic advantage hypothesis, neuroimaging studies have shown increased and wider activation while seeing dynamic expressions. The present dissertation aims to clarify the cognitive mechanism underlying this dynamic advantage and the specificity of this effect for six facial expressions of emotion. Study 1 compared behavioral and brain cortical responses to dynamic and static expressions, looking for psychophysiological correlates of the dynamic advantage. Study 2 dealt with methodological issues regarding the timing of the stimuli and the dynamic neutral conditions. Study 3 tested the hypothesis that increasing the amount of movement in the expressions would increase the allocation of attention, and compared effects of intensity in both emotional and non-emotional movements. Study 4 focused on the question of emotion specificity of brain activation during emotion recognition. Results confirmed a dynamic advantage in the classification of expressions, presumably due to more efficient allocation of attention that improved perceptual processing. The effect increased gradually by augmenting the amount of motion, in both emotional and neutral expressions, indicating a perceptual bias to attend facial movements. The enhancement was somewhat larger for happiness and reduced for surprise, but overall similar for all emotional expressions.

Introdução: O P300 é um potencial evocado auditivo que ocorre aproximadamente 300 milissegundos (ms) após a apresentação do estímulo. Geralmente, é evocado ao se utilizar o paradigma tradicional, no qual são apresentados dois estímulos perceptivelmente diferentes: um estímulo frequente (85%) e um estímulo raro (15%). Os indivíduos são orientados a indicar, de alguma maneira, a quantidade de estímulos raros que perceberam durante a realização do exame. O P300 é considerado um potencial endógeno, pois ocorre devido a um evento cognitivo (decisão da ocorrência do estímulo raro). Contudo, alguns estudos mostraram que as características acústicas do estímulo podem interferir no potencial, evidenciando uma contribuição exógena ou sensorial para evocar a resposta. Essas implicações endógenas e exógenas para evocar o P300 ainda não foram totalmente definidas. A avaliação desses aspectos específicos pode ajudar a identificar os geradores desse potencial. Objetivo: verificar o efeito da contribuição endógena e exógena para obtenção do P300, utilizando paradigma tradicional e o paradigma de omissão. Métodos: participaram desse estudo 30 indivíduos jovens adultos, normo-ouvintes sem alteração neurológica ou psiquiátrica aparente. Os indivíduos foram avaliados com o paradigma tradicional (estímulo frequente: 800 Hz; estímulo raro 1200 Hz) e com o paradigma de omissão (estímulo frequente: 800 Hz; estímulo raro: ausência de som). Cada orelha foi avaliada separadamente por ambos os paradigmas na intensidade de 80 dBNPS. Foram apresentados 300 estímulos (45 raros) em cada estimulação. Para a obtenção do P300, foi utilizado o equipamento \"Neuroscan Stim2\" com 12 eletrodos ativos no escalpo, colocados nas seguintes posições: FPz, F4, Fz, F3, C4, Cz, C3, CP6, CP5, P4, Pz e P3. O maior pico após o complexo N1-P2-N2 foi considerado como P300. A amplitude foi medida considerando a linha de base do intervalo pré-estímulo, enquanto a latência foi medida no maior pico positivo. Nesse estudo, foi utilizada a Análise de Variância (ANOVA) com medidas repetidas. Foram realizados mapas topográficos do escalpo para ambas as estimulações. Resultados: para todos os 12 eletrodos analisados nesse estudo, a média da latência em milissegundos foi significantemente menor, e a média da amplitude foi significantemente maior para o paradigma tradicional quando comparado ao paradigma de omissão. Além disso, a morfologia da onda foi mais bem definida para o paradigma tradicional. Os mapas topográficos para ambos os paradigmas mostraram uma ativação mais generalizada e mais positiva na região centro-parietal, indicando que as mesmas áreas foram ativadas em ambos os paradigmas. Conclusão: o presente estudo demonstrou que o estímulo acústico, ausente no paradigma de omissão, influencia a latência, amplitude e morfologia da onda, evidenciando uma contribuição exógena/sensorial para obtenção do potencial / Introduction: The P300 is an auditory evoked potential that occurs approximately 300 ms after the stimulus presentation. It is usually elicited by a traditional paradigm in which two perceptually different stimuli are randomly presented with different proportions - one is frequent (85%) and the other is rare (15%). The tested individual is instructed to somehow indicate the amount of rare stimuli heard. According to the literature, P300 is considered an endogenous potential since it occurs in response to a cognitive event (i.e. decision of the occurrence or not of the rare stimulus). However, few studies have shown that the acoustic characteristics of the stimuli might influence the potential, evidencing some exogenous or sensorial contribution to the response formation. The implications that endogenous and exogenous contributions have to eliciting the P300 are not fully understood yet. The assessment of their specific roles would help to identify the P300 generators. Objective: To verify the effects of the endogenous and exogenous contribution to obtain/elicit the P300 using both the traditional and the omission paradigms. Methods: Thirty normal hearing young adults, without known neurological or psychiatric disorders, participated in this study. The individuals were assessed using P300 elicited by the traditional paradigm (frequent stimulus: 800 Hz; rare stimulus: 1200Hz) and by the omission paradigm (frequent stimulus: 800 Hz; rare stimulus: absence of sound). Both paradigms were presented to one ear at a time, at 80dBSPL, and 300 stimuli (45 rare) were presented in each stimulation. The \"Neuroscan Stim2\" was used to obtain the P300 with 12 active electrodes fixed at the following positions: FPz, F4, Fz, F3, C4, Cz, C3, CP6, CP5, P4, Pz e P3. The largest peak after the N1-P2-N2 complex was considered the P300. Its amplitude was measured considering the pre-stimulation response baseline, while its latency was measured at the most positive peak. The Analysis of Variance (ANOVA) with repeated measures was used in this study. Topographic maps from the scalp to both paradigms were also analyzed. Results: To all 12 electrodes positions analyzed in this study, the mean latency (ms) was significantly earlier and the mean amplitude (?V) was significantly larger for the traditional paradigm compared to the omission paradigm. Also, better wave morphology was obtained for the traditional paradigm. The topographic maps to both paradigms has shown more generalized and positive activation at the centro-parietal region, indicating that the same brain areas were involved in both paradigms. Conclusion: The current study has demonstrated that the acoustic stimulus, absent on the omission paradigm, have an impact on the wave formation in respect to its latency, amplitude and morphology, evidencing the influence of sensorial information to the P300

Les difficultés de théorie de l’esprit (ToM) associées à la schizophrénie (SZ) et la schizotypie (Szt) seraient dues à un trouble élémentaire de traitement du contexte. Or, traiter le contexte engagerait deux types de processus inégalement atteints dans la SZ: les processus prédictifs (génération de prédictions) seraient préservés et les processus intégratifs (intégration a posteriori des informations nouvelles avec le contexte) seraient altérés. Ces processus sont mobilisés lors de la production d’inférences et reflétés par la modulation de la N400 ou de la P600. À l’aide de mesures comportementales et électrophysiologiques, l’objectif de ce travail était de: a) vérifier l’inégale atteinte de ces processus dans la Szt, b) évaluer si ce pattern d’inégale atteinte est observé lors d’une tâche de production d’inférences intentionnelles (PII), c) faciliter la mobilisation des processus altérés par le renforcement du contexte (sémantique, ajout d’un indice social). L’étude réalisée avec un paradigme d’amorçage sémantique en contexte mot confirme l’altération spécifique des processus intégratifs dans la Szt. La suite des études, conduite autour d’une tâche de PII reposant sur les processus prédictifs ou intégratifs dans la SZ et la Szt, montre: 1) des difficultés de PII lorsqu’elle mobilise les processus intégratifs, 2) une réduction de ces difficultés par le renforcement sémantique et 3) que l’ajout d’un indice social pourrait faciliter le traitement du contexte. Ainsi, la PII n’est pas totalement altérée dans la Szt et la SZ. Les études futures devraient considérer cette inégale atteinte des processus en ToM pour aider les patients à attribuer des intentions à autrui. / Theory of mind (ToM) impairments in schizophrenia (SZ) and in schizotypy (Szt) may stem from a context-processing deficit. However, treating the context would involve two types of processes differently affected impacted in SZ: predictive strategy (generation of expectations) would be preserved and integrative strategy (retroactive integration of new information with the context) would be altered. These processes are mobilized during inference generation tasks and reflected by modulations of the N400 and P600 components. Using behavioral and electrophysiological measures, the aim of this thesis was to: (a) confirm the unequal alteration of these processes in the Szt, (b) assess whether this pattern of unequal alteration is observed in intentional inference production tasks (IIP), and (c) facilitate the mobilization of altered processes by increasing the contextual constraints (semantic constraint, contextual reinforcement by social cue). Using a semantic priming task in word context, a first study showed that integrative processes are specifically altered in Szt. Subsequent studies were based on IIP task in which the inference production involved predictive processes or integrative processes. Results showed that: (1) difficulties were observed only when IIP involved integrative processes, (2) semantic constraints decreased these difficulties and (3) context processing may be facilitated by the addition of a social cue. Thus, IIP is not totally altered in Szt and SZ. Future studies should consider this unequal impact of ToM processes to help patients attribute intentions to others.

Objective: Attention Bias Modification Training (ABMT) for anxiety aims to train attention away from threatening stimuli and toward neutral stimuli. Although ABMT shows promising anxiety reduction effects in children and adolescents, no study has examined its influence on neural indicators of attention measured using event-related potentials (ERPs) in children or adolescents (i.e., youths). The present study examined the influence of ABMT on the P1, N170, P2 and P3 ERP components during completion of the emotional faces dot probe task in youths with anxiety disorders who failed to respond to cognitive behavioral therapy. Method: Thirty youths (M age = 11.97, SD = 2.89) with primary DSM-IV-TR anxiety disorders completed the dot probe task while undergoing electroencephalogram (EEG) to obtain ERPs before, immediately after, and eight weeks after eight sessions of either ABMT (n = 14) or a control task regimen (CT), (n = 16). Results: At post-treatment, statistically significant effects were found for P1 and P3 mean amplitudes: P1 was significantly higher during trials showing neutral-neutral (NN) face pairs in the ABMT arm than in the CT arm; P3 was significantly higher during trials showing NN face pairs than during trials showing neutral-threat (NT) face pairs in the ABMT arm, but not the CT arm. At eight-week follow-up, participants in both arms showed significantly higher (more negative) N170 responses for NN trials than for NT trials. Conclusions: Attention Bias Modification Treatment led to increases in neural processing of neutral stimuli in early and late stage attentional processing, as measured by the P1 and P3 components, respectively. These components during the dot probe task are promising neural markers of ABMT’s effects on attentional processing in youth with anxiety disorders.

L’addiction à l’alimentation (AA) est un concept ancien, mais encore sujet de controverses qui toucherait 18 à 24 % des obèses. Dans cette thèse, nous nous sommes intéressés aux intrications entre régulations du comportement alimentaire, addiction et AA, afin de mieux comprendre les mécanismes liés à la désinhibition de la prise alimentaire. Notre travail a conduit à plusieurs résultats : 1) Une revue de la littérature a permis de montrer l’existence d’interaction étroite entre les niveaux de régulation du comportement alimentaire et comment AA pourrait en être un exemple de dérégulation. 2) Une étude de cohorte a permis de démontrer l’existence de caractéristiques cliniques communes entre addictions et AA et celle d’un probable transfert d’addiction de la nicotine vers l’alimentation. 3) Sur le plan expérimental, nous avons montré qu’il existe des perturbations des ondes P300 et N200, dans l’obésité et la désinhibition alimentaire, proches de celles observées dans les addictions. 4) Enfin, nos résultats suggèrent le rôle potentiel de la ghréline comme marqueur de risque de trouble du comportement alimentaire. Ce travail ouvre des perspectives sur le plan expérimental, avec la suggestion de groupes contrôles plus pertinents ; cliniques, avec la création d’un potentiel test de dépistage rapide ; thérapeutiques, avec la mise en place d’un essai thérapeutique par tDCS / Food addiction (FA) is an old concept, but still subject to controversy. It affects 18 to 24% of obese people. In this thesis, we are interested in overlaps between food behavior regulation, addiction and FA, in order to better understand the mechanisms linked to food intake disinhibition. Our work leads to several results: 1) A review of the literature has shown the existence of close interaction between eating behavior regulation levels and how FA could be an example of their disturbance. 2) A cohort study demonstrated the existence of common clinical features between addiction and FA and a probable addiction transfer from nicotine to food. 3) From an experimental point of view, we have shown that there are disturbances of P300 and N200 ERP, in obesity and food disinhibition, close to those observed in addictions. 4) Finally, our results suggest the potential role of ghrelin as a marker for eating disorders increased risk. This work opens experimental perspectives, with the suggestion of more relevant control groups; clinical perspectives, with the creation of a screening tool; therapeutics perspectives, with the establishment of a therapeutic trial by tDCS

In dieser Dissertation zeige ich anhand einer Reihe von Beispielen, wie das Langzeitgedächtnis die perzeptuelle Verarbeitung beeinflussen kann. Anhand einer Aufgabe zur visuellen Aufmerksamkeit verdeutliche ich, inwiefern episodische Erinnerungen perzeptuelle Distrakoreffekte reduzieren können. In Experiment 1 sollten Versuchspersonen zuvor gelernte Worte entweder ins Gedächtnis zu rufen oder die Erinnerung an die Worte zu unterdrücken. Anschließend mussten sie unter Zeitdruck neue, bisher nicht präsentierte Worte semantisch einordnen, wobei die Zielworte von den zuvor abgerufenen oder unterdrückten Worten flankiert waren. Da die flankierenden Worte für die semantische Entscheidungsaufgabe irrelevant und die Versuchspersonen instruiert worden waren, diese zu ignorieren, kann von einem perzeptuellen Distraktoreffekt ausgegangen werden. Distraktoreffekte waren für zuvor unterdrückte Gedächtnisinhalte im Vergleich zur abgerufenen Gedächtnisinhalten deutlich reduziert, was nahelegt, dass episodische Gedächtnisinhalte die Wahrnehmung beeinflussen. Auf dieser Erkenntnis aufbauend zeige ich in Experiment 2, wie die suppressionsinduzierte Reduktion der Verarbeitung von Distraktorreizen durch individuelle Differenzen maskiert werden kann. Schließlich wurden den Versuchspersonen in Experiment 3 in einer „Attentional-Blink“-Aufgabe unbekannte Objekte als zweites von zwei aufeinander folgenden Zielobjekten dargeboten. Versuchspersonen konnten Objekte, die mit einer neu gelernten semantischen Information assoziiert waren, besser erkennen als Objekte, die mit minimaler Information assoziiert waren. Dieser Effekt ging mit einer Modulation der ereigniskorrelierten Potenziale 100ms nach Erscheinen des Reizes einher. Diese Ergebnisse zeigen, dass Inhalte aus dem Langzeitgedächtnis Wahrnehmungsprozesse beeinflussen können und leisten damit einen weiteren Beitrag zur Erkenntnis, dass die Wahrnehmung gegenüber höheren Kognitionen nicht unabhängig ist. / Numerous studies are emerging which suggest that long-term memories can influence early perceptual processing. Notwithstanding, these finding have come under fire from critics who view perceptual processing as independent of cognition. In this dissertation I demonstrate novel instances of long-term memory effects on perceptual processing, both in the context of an attentional task where I look at the extent to which episodic memory can reduce perceptual distraction and in a conscious detection task where I assess the effect of semantic knowledge on peoples ability to consciously detect briefly presented objects. In experiment one, participants retrieved or suppressed previously memorised words. Following this task, participants made speeded semantic judgments on novel target words that were flanked by the words that had previously undergone suppression or retrieval. Because the flanking words were irrelevant to the semantic judgment and were supposed to be ignored, any influence of their presence on semantic judgment speed can be taken as a marker of perceptual distraction. Results showed that the tendency for flankers to distract from target processing was markedly reduced if those flankers had undergone suppression. In experiment two, I expanded upon this finding by showing how this suppression-induced reduction in distractor processing can be masked by individual differences. Finally, in experiment three, I presented pictures of novel objects to participants as the second of two targets in an attentional blink paradigm. Results showed that participants were able to perceive objects associated with newly acquired semantic knowledge better than objects associated with minimal knowledge, a finding that was associated with a modulation of event-related brain potentials 100 msec after stimulus onset. Taken together, these experiments contribute to the growing body of evidence showing that information from long-term memory can influence perceptual processing.