A substantial amount of behavioural, genetic, and neurophysiological data suggest that Attention Deficit Hyperactivity Disorder (ADHD) is influenced by an underlying abnormality in the midbrain dopamine system. A previous study found that children with ADHD are unusually sensitive to the salience of rewards, mediated in part by the dopamine system (Holroyd, Baker, Kerns & Mueller, 2008). The current study aimed to replicate and expand upon the previous finding using event-related potentials (ERP) recorded from typically developing children and children with ADHD as they navigated a “virtual T-Maze” in two conditions differing on reward saliency. Children also completed a behavioural task designed to measure decision making and sensitivity to reward and punishment. Both groups of children responded to the behavioural task in a way that is indicative of increased sensitivity to reward. Unlike the previous study, the salience of reward as reflected in the ERP did not have an effect on either children with ADHD or typically developing children. However, both groups displayed a larger error-related negativity (ERN) in the condition presented second.

Tokie regimieji dirgikliai kaip Necker’io gardelė įdomūs tuo, kad yra dviprasmiai bei sukelia trimatės erdvės pokyčio suvokimą. Remiantis suvokimo apkrovos teorija papildoma užduotis turėtų keisti šį suvokimą. Šio darbo tikslas buvo ištirti dviprasmių ir nedviprasmių gardelių suvokimą skirtingos suvokimo apkrovos užduotyse. I eksperimente dalyvavo 18 studentų (9 vyrai ir 9 moterys). Buvo tiriama didelės ir mažos suvokimo apkrovos įtaka reversijų suvokimui. II eksperimente dalyvavo 9 tiriamieji (7 vyrai ir 2 moterys). Tyrimo eiga buvo tokia pati kaip I eksperimento, bet skyrėsi užduotys: vienoje užduotyje raidžių nebuvo (normalus stebėjimas), kitoje užduotyje raidės buvo, bet į jas nereikėjo kreipti dėmesio. Palyginus abiejų tyrimų rezultatus nustatyta, kad bet kokia suvokimo apkrova panaikina Reversijos neigiamumą subjektyvaus pasikeitimo atveju. Realaus pasikeitimo bloke Reversijos neigiamumas buvo gautas, bet nepriklausė nuo apkrovos. Reversijos teigiamumui neturi įtakos nei suvokimo apkrova, nei suvokimo trukdis, tuo tarpu esant suvokimo trukdžiui Reversijos neigiamumas išnyksta tiek realaus, tiek Necker’io gardelės pasikeitimo atvejais. / Ambiguous visual stimuli such as the Necker lattice are interesting because they can cause apparent changes in our perception. According to the perceptual load theory, complementary tasks would be able to modify the amount of attention paid to this perception. The aim of this study was to investigate the perception of ambiguous and unambiguous lattices under different perceptual load tasks. Eighteen participants (9 men) took part in experiment I. The impact of high and low perceptual loads on perception of reversals was studied. 9 subjects (7 men) participated in experiment II. The experimental procedure was the same as in experiment I, but the tasks were a bit different: task without letters (normal observation) and task with letters distracters. Participants were told not to pay attention to letters in experiment II. A comparison of the results of these two experiments revealed that high and low perceptual loads eliminate Reversal Negativity in Necker change condition. Reversal Negativity was found in Real change condition, but it was load-independent. Neither perceptual load, nor load-resembling distractor have any effects on Reversal Positivity, however, Reversal Negativity was suppressed by load-resembling distractors both in Real change and in Necker change conditions.

The studies investigated the impact of predictive visual information about the pitch and location of a forthcoming sound on the sound processing. In Symbol-to-Sound matching paradigms, symbols induced predictions of particular sounds. The brain’s error signals (IR and N2b components of the event-related potential) were measured in response to occasional violations of the prediction, i.e. when a sound was incongruent to the corresponding symbol. IR and N2b index the detection of prediction violations at different levels, IR at a sensory and N2b at a cognitive level. Participants evaluated the congruency between prediction and actual sound by button press. When the prediction referred to only the pitch or only the location feature (Exp. 1), the violation of each feature elicited IR and N2b. The IRs to pitch and location violations revealed differences in the in time course and topography, suggesting that they were generated in feature-specific sensory areas. When the prediction referred to both features concurrently (Exp. 2), that is, the symbol predicted the sound´s pitch and location, either one or both predictions were violated. Unexpectedly, no significant effects in the IR range were obtained. However, N2b was elicited in response to all violations. N2b in response to concurrent violations of pitch and location had a shorter latency. We conclude that associative predictions can be established by arbitrary rule-based symbols and for different sound features, and that concurrent violations are processed in parallel. In complex situations as in Exp. 2, capacity limitations appear to affect processing in a hierarchical manner. While predictions were presumably not reliably established at sensory levels (absence of IR), they were established at more cognitive levels, where sounds are represented categorially (presence of N2b).

Deafferented cortical visual areas exhibit topographical plasticity such that their constituent neural populations adapt to the loss of sensory input through the expansion and eventual remapping of receptive fields to new regions of space. Such representational plasticity is most compelling in the long-term (months or years) but begins within seconds of retinal deafferentation (short-term plasticity). The neural mechanism proposed to underlie topographical plasticity is one of disinhibition whereby long-range horizontal inputs are "unmasked" by a reduction in local inhibitory drive. In this dissertation, four experiments investigated the neural mechanisms of short-term visual plasticity and disinhibition in humans using a combination of psychophysics and event-related potentials (ERPs). Short-term visual plasticity was induced using a stimulus-induced analog of retinal deafferentation known as an artifical scotoma. Artificial scotomas provide a useful paradigm for the study of short-term plasticity as they induce disinhibition but are temporary and reversible. Experiment 1 measured contrast response functions from within the boundaries of an artificial scotoma and evaluated them relative to a sham control condition. Changes in the contrast response function suggest that disinhibition can be conceived of in terms of two dependent but separable processes: receptive field expansion and unrestricted neural gain. A two-process model of disinhibition is proposed. A complementary ERP study (Experiment 2) recorded visual evoked potentials elicited by probes appearing within the boundaries of an artificial scotoma. Results revealed a neural correlate of disinhibition consistent with origins in striate and extrastriate visual areas. Experiment 3 and 4 were exploratory examinations of the representation of space surrounding an artificial scotoma and revealed a neural correlate of invading activity from normal cortex. Together, the results of these four studies strengthen the understanding of the neural mechanisms that underlie short-term plasticity and provide a conceptual framework for their evaluation.

The successful execution of goal-directed movement requires the evaluation of many levels of errors. On one hand, the motor system needs to be able to evaluate ‘high-level’ errors indicating the success or failure of a given movement. On the other hand, as a movement is executed the motor system also has to be able to correct for ‘low-level’ errors - an error in the initial motor command or change in the motor command necessary to compensate for an unexpected change in the movement environment. The goal of the present research was to provide electroencephalographic evidence that error processing during motor control is evaluated hierarchically. The present research demonstrated that high-level motor errors indicating the failure of a system goal elicited the error-related negativity, a component of the event-related brain potential (ERP) evoked by incorrect responses and error feedback. The present research also demonstrated that low-level motor errors are associated with parietally distributed ERP component related to the focusing of visuo-spatial attention and context-updating. Finally, the present research includes a viable neural model for hierarchical error processing during motor control.

H προβολή υποσυνείδητων μηνυμάτων είναι η διαδικασία έκθεσης ερεθισμάτων κάτω από το κατώφλι της συνειδητοποίησης. Με τον τρόπο αυτό μπορεί να επηρεαστούν οι σκέψεις, τα συναισθήματα και ενέργειες του ανθρώπου. Η υποσυνείδητη αντίληψη συμβαίνει όταν οι πληροφορίες αποθηκεύονται στο ανθρώπινο μυαλό, χωρίς ο δέκτης να έχει συνειδητά επίγνωση του προβλήματος. Οι πληροφορίες φτάνουν στο μυαλό, γιατί ενώ δεν είναι συνειδητά αντιληπτές, γίνονται αντιληπτές από το υποσυνείδητο κομμάτι του εγκεφάλου. Αντικείμενο της παρούσας διπλωματικής εργασίας είναι η αποτίμηση των πιθανών διαφορών στις καταγραφές ηλεκτροεγκεφαλογραφήματος (ΕΕG) και προκλητών δυναμικών (ERPs) κατά την υποβολή ενός ατόμου σε οπτικά υποσυνείδητα ερεθίσματα σε σύγκριση με καταγραφές χωρίς ερέθισμα. Στην εργασία χρησιμοποιήθηκε ένα ερευνητικό πρωτόκολλο το οποίο εξετάζει το πώς επηρεάζουν τα υποσυνείδητα ερεθίσματα τη λήψη αποφάσεων και την εγκεφαλική λειτουργία. Στο πρώτο μέρος της εργασίας (κεφάλαια 1 και 2) γίνεται μια συνοπτική αναφορά στις κυριότερες μεθόδους απεικόνισης εγκεφάλου, όπως το ηλεκτροεγκεφαλογράφημα και την λειτουργική απεικόνιση Μαγνητικού Συντονισμού καθώς και στον συνδυασμό τους για πιο ικανοποιητικά αποτελέσματα. Το κεφάλαιο 3 αναφέρεται κυρίως σε θέματα σχετικά τα προκλητά δυναμικά, καθώς και την υποσυνείδητη αντίληψη. Στο κεφάλαιο 4 περιγράφεται η πειραματική διαδικασία και η μετρητική διάταξη που χρησιμοποιήθηκε καθώς και η παρουσίαση της επεξεργασίας των μετρήσεων μέσω του eeglab. Τέλος, στο κεφάλαιο 5 παρουσιάζονται τα αποτελέσματα της επεξεργασίας σε διαγράμματα προκλητών δυναμικών και φασματικής ισχύος καθώς επίσης και τα συμπεράσματα της εργασίας αυτής. / The display of subliminal messages is the process of stimuli exposure below the threshold of awareness. Through this procedure the thoughts, feelings and actions of a human can be influenced. The subliminal perception occurs when information stored in the human mind without the receiver being consciously aware of it. The information reaching the brain is perceived by the subconscious part of the brain. The object of this diploma thesis is to assess the possible differences in electroencephalogram (EEG) and event - related potentials (ERPs) recordings during the presentation of visual subliminal stimuli compared to non – subliminal conditions. A protocol that examines how subliminal stimuli influence the decision making and the cerebral operation is used. In the first part of the thesis (chapters 1 and 2) there is a brief review of the main brain imaging methods such as EEG and fMRI as well as the combination of them. Chapter 3 reveals issues about event - related potentials and mostly about subliminal perception. In chapter 4, the experiment and the measuring devices used are described, and there is also a presentation of the analysis by using the eeglab. Finally, chapter 5 includes the results of analysis on event - related potential and spectral power graphs, as well as the conclusions of this work.

L’hypothèse de ce travail est que les sujets schizophrènes souffrant d’hallucinations auditives verbales perçoivent leur propre voix comme une voix étrangère. L'objectif de notre travail est donc d'étudier les réponses électrophysiologiques évoquées par la voix des participants et celle d’une personne inconnue. Nos résultats chez les sujets sains montrent que nous allouons moins de ressources attentionnelles automatiques à notre propre voix que par rapport à une voix inconnue. Cet effet d’atténuation de l’orientation automatique de l’attention pour sa propre voix n’est pas observé chez les patients schizophrènes. De plus, conformément à notre hypothèse initiale, cet effet est d’autant plus faible que la sévérité des hallucinations est forte. / The hypothesis of this study was that schizophrenic patients with auditory verbal hallucinations perceive their own voices as alien voices. The aim of the study was to investigate the electrophysiological responses evoked by participants’own voices and those of unknown individuals. Our results in healthy subjects showed that they allocated fever automatic attentional resources to their own voices than to unfamiliar voices. This attenuation effect of the automatic orientation of attention to own voice was not observed in schizophrenic patients. In addition, in agreement with our initial hypothesis, the attenuation decreased even further as the hallucinations became more severe.

L’intolérance au changement est fréquemment observée dans l'autisme et s'exprime dans toutes les modalités sensorielles. L’objectif de ce travail était d’étudier la perception automatique du changement visuel chez des enfants et adultes avec autisme via un paradigme oddball passif. En utilisant l’électrophysiologie, des réponses atypiques aux changements visuels mêmes mineurs, ont été mises en évidence dans l’autisme, quel que soit l'âge, suggérant une hyperdistractibilité des patients. De plus, l’utilisation de l’IRMf a permis de révéler, lors de la présentation d’un changement visuel, une hyperactivation du cortex sensoriel associée à une hyperactivation du cortex cingulaire antérieur, d’autant plus élevée que les patients avaient des traits autistiques marqués. Cette étude suggère donc qu’une hyper-réactivité sensorielle associée à des troubles de l’attention visuelle sélective contribueraient aux troubles de perception du changement et aux difficultés d'adaptation dans l’autisme. / Resistance to change is often reported in autism spectrum disorders (ASD) and may occur in all sensory modalities. The aim of the present work was to investigate automatic visual change detection in children and adults with ASD using a passive oddball paradigm. Whatever the age, electrophysiological results showed atypical responses to, even minor, changes, suggesting an hyper distractibility in the patients. Besides, fMRI results revealed hyperactivation of the sensory cortex associated with hyperactivation of the anterior cingulate cortex in adults with ASD, the latest being correlated with the degree of autistics symptoms. These studies thus suggest that a sensory hyper-reactivity associated with visual selective attention deficits might contribute to atypical change perception and adaptation in ASD.

Des réactions inhabituelles et disproportionnées face aux changements survenant de manière imprévisible dans l’environnement sont observées dans l’autisme. L’objectif de ce travail est de caractériser chez des adolescents et des jeunes adultes avec autisme les mécanismes neurophysiologiques impliqués dans le traitement d’un contexte visuel prédictif à partir de l’analyse des potentiels évoqués et des oscillations cérébrales. L’étude de la maturation au cours de l’adolescence chez le sujet au développement typique montre que les mécanismes de prédiction sont matures dès l’âge de 12 ans. Les personnes avec autisme parviennent à extraire l’information pertinente dans un contexte simple, certain et explicite, et à l’utiliser pour se préparer à la survenue d’un événement afin d’y avoir une réponse adaptée. Ces résultats suggèrent que les mécanismes de traitement d’un contexte visuel prédictif dans un contexte certain sont préservés dans l’autisme. Toutefois, les personnes avec autisme sur-anticipent les stimulations imprévisibles, en accord avec leur impression de surcharge sensorielle. Elles présentent également des difficultés pour moduler de manière flexible les activités corticales en fonction du niveau d’incertitude du contexte, en accord avec le défaut d’adaptation à un monde en perpétuel changement. Ce travail suggère qu’un dysfonctionnement des mécanismes de prédiction dans un contexte incertain pourrait fournir un cadre théorique permettant de mieux comprendre les particularités rencontrées dans l'autisme. / Individuals with autism react in an unusual and disproportionate way if unpredictable changes occur in their environment. The aim of the present work is to investigate brain mechanisms involved in visual predictive context processing in adolescents and adults with autism using analysis of event-related potentials and brain oscillations. The developmental study shows that mechanisms of prediction are mature by the age of 12 in typically developing adolescents. Individuals with autism are able to extract relevant information from the stimulus train in a simple, certain and explicit context, to use it in order to anticipate the occurrence of an event and to have an appropriate response, suggesting preserved extraction and use of predictive information during a certain context. However, individuals with autism over-anticipate stimuli during an uncertain context, consistent with the sense of being overwhelmed by incoming information, and also cannot flexibly modulate cortical activity according to changing levels of uncertainty, in agreement with atypical adaptation in an ever-changing world. This work suggests that a dysfunction of predictive processing in an uncertain context might provide a theoretical framework to better understand the symptoms encountered in autism.

Affect and cognition have traditionally been considered mutually exclusive domains and their study has evolved into two separate research fields. In recent years, however, there is increasing evidence of affective modulations of cognitive processes and interest in the study of affective cognition has grown. This thesis presents analyses of data collected in four mixed-design experiments between 2009 and 2011, which were designed to investigate affective memory and its electrophysiological correlates, individual differences in said affective memory and electrophysiological correlates, the time-course of affective memory and attentional disengagement from affective stimuli respectively. The first aim of the research presented here was to further understanding of how affective content influences picture processing and memory. Event-related potentials (ERPs) provide a valuable tool for the investigation of modulations of cognitive processes, as their excellent temporal resolution allows for the dissociation between different processes contributing to behavioural outcomes. Several important results for the study of affective cognition are reported: The late positive potential (LPP) was shown to be modulated differentially by affective content when compared to a behavioural attentional disengagement task. While the behavioural measure of attention replicated findings from participants’ self-report of arousal, LPP enhancement did not. This novel finding demonstrates that the affective modulation of the LPP cannot be used as an electrophysiological marker of slowed attentional disengagement as is common in the literature. In the domain of recognition memory, affective modulation of performance was shown to be time-sensitive, with effects developing faster for negative than for positive picture content. Affective pictures were associated with a less conservative response bias than neutral pictures but only negative pictures elicited better discrimination performance, driven by an increased in the rate of “remembered” as compared to merely familiar pictures. This was reflected in an increase of the ERP old/new effect for negative pictures in the 500 to 800ms time window, the purported correlate of recollection. The late right-frontal old/new effect between 800 and 1500 ms post stimulus onset was shown to be attenuated by affective content, supporting the interpretation of the late right-frontal effect as a correlate of relevance detection over a retrieval success interpretation. In combination, the findings add weight to the conclusion that affective content enhances memory through selective memory sparing for affective stimuli. Novel evidence for gender differences in affective cognition was found. Comparisons between female and male participants revealed that the affective modulation of the late right-frontal effect differs between the genders, underlining the importance of assessing and understanding gender differences as part of the study of affective cognition. Brain-derived neurotrophic factor (BDNF) gene val66met single nucleotide polymorphism (SNP), a small genetic change that affects the functioning of BDNF, a protein that plays an important role in neuron growth, differentiation and survival, is shown here to also affect the interaction of affect and cognition. BDNF val66met genotype modulated the early “familiarity” old/new effect selectively in response to positive pictures. The present study clearly demonstrates the value of the ERP technique in the investigation of individual differences in affective and cognitive processing and the need to take such individual differences into account as part of the endeavour to fully understand the mechanisms of affective processing, cognition and affective cognition. A better understanding of the role of gender and genetic differences in the affective modulation of affective processing and memory will have important practical implications in fields where affect and cognition interact.