This dissertation focuses on two specific problems related to the design of parametric signal classifiers: dimensionality reduction to overcome the curse of dimensionality and information fusion to improve classification by exploiting complementary information from multiple sensors or multiple classifiers. Dimensionality reduction is achieved by introducing a strategy to rank and select a subset of principal component transform (PCT) coefficients that carry the most useful discriminatory information. The criteria considered for ranking transform coefficients include magnitude, variance, inter-class separation, and classification accuracies of individual transform coefficients. The ranking strategy not only facilitates overcoming the dimensionality curse for multivariate classifier implementation but also provides a means to further select, out of a rank-ordered set, a smaller set of features that give the best classification accuracies. Because the class-conditional densities of transform feature vectors are often assumed to be multivariate Gaussian, the dimensionality reduction strategy focuses on overcoming the specific problems encountered in the design of practical multivariate Gaussian classifiers using transform feature vectors. Through experiments with event related potentials (ERPs) and ear pressure signals, it is shown that the dimension of the feature space can be decreased quite significantly by means of the feature ranking and selection strategy. Furthermore, the resulting Gaussian classifiers yield higher classification accuracies than those reported in previous classification studies on the same signal sets. Amongst the four feature selection criteria, Gaussian classifiers using the maximum magnitude and maximum variance selection criteria gave the best classification accuracies across the two sets of classification experiments. For the multisensor case, dimensionality reduction is achieved by introducing a spatio-temporal array model to observe the signals across channels and time, simultaneously. A two-step process which uses the Kolmogrov-Smirnov test and the Lilliefors test is formulated to select the array elements which have different Gaussian densities across all signal categories. Selecting spatio-temporal elements that fit the assumed model and also statistically differ across the signal categories not only decreases the dimensionality significantly but also ensures high classification accuracies. The selection is dynamic in the sense that selecting spatio-temporal array elements corresponds to selecting samples of different sensors at different time-instants. Each selected array element is classified using a univariate Gaussian classifier and the resulting decisions are fused into a decision fusion vector which is classified using a discrete Bayes classifier. The application of the resulting dynamic channel selection-based classification strategy is demonstrated by designing and testing classifiers for multi-channel ERPs and it is shown that strategy yields high classification accuracies. Most noteworthy of the two dimensionality reduction strategies is the fact that the multivariate Gaussian signal classifiers developed can be implemented without having to collect a prohibitively large number of training signals simply to satisfy the dimensionality conditions. Consequently, the classification strategies can be beneficial for designing personalized human-machine-interface (HMI) signal classifiers for individuals from whom only a limited number of training signals can reliably be collected due to severe disabilities. The information fusion strategy introduced is aimed at improving the performance of signal classifiers by combining signals from multiple sensors or by combining decisions of multiple classifiers. Fusion classifiers with diverse components (classifiers or data sets) outperform those with less diverse components. Determining component diversity, therefore, is of the utmost importance in the design of fusion classifiers which are often employed in clinical diagnostic and numerous other pattern recognition problems. A new pairwise diversity-based ranking strategy is introduced to select a subset of ensemble components, which when combined, will be more diverse than any other component subset of the same size. The strategy is unified in the sense that the components can be either polychotomous classifiers or polychotomous data sets. Classifier fusion and data fusion systems are formulated based on the diversity selection strategy and the application of the two fusion strategies are demonstrated through the classification of multi-channel ERPs. From the results it is concluded that data fusion outperforms classifier fusion. It is also shown that the diversity-based data fusion system outperforms the system using randomly selected data components. Furthermore, it is demonstrated that the combination of data components that yield the best performance, in a relative sense, can be determined through the diversity selection strategy.

Mounting evidence has suggested that structures such as the anterior cingulate cortex (ACC) and other areas within the medial-frontal cortex are part of a reinforcement learning system responsible for the optimization of behaviour (Holroyd & Coles, 2002). However, we also learn without reinforcement and it has been less clear what neural structures are recruited in these instances. The P300 component of the human event-related brain potential (ERP) has been intensely researched in regards to context updating and the processing of novel stimuli (Spencer, Dien, & Donchin, 2001). Here, I sought to elaborate on the role of the P300 ERP component in implicit learning of stimulus frequencies – learning driven by the stimulus itself and not reward feedback. I propose over the course of three experiments that I have provided evidence indicating that the P300 and its neural sources play a role in feedback-free learning mechanisms. Specifically, in a feedback-free paradigm participants are shown to learn stimulus frequencies. While this occurs, P300 amplitude scales in line with participant behaviour and stimulus frequency. A common trend is revealed in how quickly this amplitude scaling occurs, suggesting further mechanisms are at play. Trial-by-trial analysis ultimately shows that behavioural prediction error formula and neural correlate prediction errors utilize a nearly identical function. These trends hold even in a passive auditory task in which the participant is fully distracted. / Graduate

Processos de recuperação de memórias são frequentemente investigados através de técnicas de monitoração da atividade cerebral. Na presente tese, é desenvolvido inicialmente um exame sobre a utilização no Brasil de uma ferramenta chamada Potenciais Relacionados ao Evento (PRE). Em seguida, são descritos dois estudos que investigaram processos de recuperação de items neutros associados a contextos emocionais versus contextos neutros. Em ambos os PREs foram extraídos. Através do estudo de revisão sobre PRE no Brasil, constatou-se que esta abordagem de pesquisa ainda é pouco desenvolvida neste país. Através dos outros dois estudos, demonstrou-se a presença de dois efeitos emocionais: um efeito de início rápido (200 ms) e um tardío (iniciando entre 500 e 800 ms). Estes efeitos sugerem que o cérebro responde a items associados a contextos emocionais antes de realizar um processo de recuperação envolvendo a consciência, e indicam que os processos pós-recuperação são modulados pela propriedade emocional dos items. / Memory retrieval processes are frequently investigated by brain monitoring techniques. In the present dissertation, a review on the state of the art of Event-related potentials (ERP) research in Brazil is initially conducted. It is followed by the report of two ERP studies investigating the retrieval processes of neutral items associated to emotional versus neutral contexts. The exam of the Brazilian ERP research demonstrated that this approach still needs to be properly developed in this country. Both ERP studies demonstrated the presence of two main emotional ERP effects: an early onset effect (200 ms) and a late onset effect (onsetting between 500 and 800 ms). These effects suggest that the brain reacts to items associated to emotional contexts before the onset of conscious retrieval processes. They also indicate that post-retrieval processes are modulated by the emotional properties acquired by the items.

Parents and Children Making Connections – Highlighting Attention (PCMC-A) is a dual-generation intervention program for families from lower socioeconomic status backgrounds that includes parenting training for parents and attention training for preschool-aged children. PCMC-A has been shown to impact brain function for selective attention in children, the ability to enhance relevant information and suppress competing, distracting information. With the goal of increasing our understanding of how PCMC-A operates to promote gains in child brain function for selective attention, the main objective of this dissertation was to test intervention-related changes in supportive parenting behaviors as an explanatory mechanism for the effect of PCMC-A on neural indices of selective attention. To better understand the profile of those who benefit from PCMC-A to different extents, we also examined moderators of the effect of PCMC-A on supportive parenting and on child brain function for selective attention. These questions were examined as part of the randomized controlled trial to evaluate the impact of PCMC-A on Head Start preschoolers and their parents, employing a multi-method approach. We found that participation in PCMC-A led to increases in specific aspects of supportive parenting behaviors coded from observed parent-child interactions, which were moderated by child and mother characteristics at the pre-assessment, including mother reports of child behavior problems, child age, and maternal interactive language use. We also replicated with a larger sample an effect of PCMC-A on child selective attention measured using the event-related potential technique, which was moderated by mother reports of child social skills at the pre-assessment. Even though we documented changes in both of these outcomes as a function of PCMC-A, we did not find evidence that changes in supportive parenting explained gains in child selective attention, suggesting that other explanatory mechanisms may be at play. Together, the findings of the present dissertation characterize the effect of PCMC-A on supportive parenting behaviors and child selective attention, begin to paint a picture of the families who benefit most and least from this intervention, and contribute to our understanding of the mechanisms through which PCMC-A impacts child brain function for selective attention. This dissertation includes unpublished co-authored material.

Processos de recuperação de memórias são frequentemente investigados através de técnicas de monitoração da atividade cerebral. Na presente tese, é desenvolvido inicialmente um exame sobre a utilização no Brasil de uma ferramenta chamada Potenciais Relacionados ao Evento (PRE). Em seguida, são descritos dois estudos que investigaram processos de recuperação de items neutros associados a contextos emocionais versus contextos neutros. Em ambos os PREs foram extraídos. Através do estudo de revisão sobre PRE no Brasil, constatou-se que esta abordagem de pesquisa ainda é pouco desenvolvida neste país. Através dos outros dois estudos, demonstrou-se a presença de dois efeitos emocionais: um efeito de início rápido (200 ms) e um tardío (iniciando entre 500 e 800 ms). Estes efeitos sugerem que o cérebro responde a items associados a contextos emocionais antes de realizar um processo de recuperação envolvendo a consciência, e indicam que os processos pós-recuperação são modulados pela propriedade emocional dos items. / Memory retrieval processes are frequently investigated by brain monitoring techniques. In the present dissertation, a review on the state of the art of Event-related potentials (ERP) research in Brazil is initially conducted. It is followed by the report of two ERP studies investigating the retrieval processes of neutral items associated to emotional versus neutral contexts. The exam of the Brazilian ERP research demonstrated that this approach still needs to be properly developed in this country. Both ERP studies demonstrated the presence of two main emotional ERP effects: an early onset effect (200 ms) and a late onset effect (onsetting between 500 and 800 ms). These effects suggest that the brain reacts to items associated to emotional contexts before the onset of conscious retrieval processes. They also indicate that post-retrieval processes are modulated by the emotional properties acquired by the items.

There are multiple factors that influence auditory steaming. Some, like frequency separation or rate of presentation, have effects that are well understood while others remain contentious. Human behavioural studies and event-related potential (ERP) studies have shown dissociation between a pre-attentive sound segregation process and an attention-dependent process in forming perceptual objects and streams. This thesis first presents a model that synthetises the processes involved in auditory object creation. It includes sensory feature extraction based on research by Bregman (1990), sensory feature binding through an oscillatory neural network based on work by Wang (1995; 1996; 1999; 2005; 2008), work by Itti and Koch (2001a) for the saliency map, and finally, work by Wrigley and Brown (2004) for the architecture of single feature processing streams, the inhibition of return of the activation and the attentional leaky integrate and fire neuron. The model was tested using stimuli and an experimental paradigm used by Carlyon, Cusack, Foxton and Robertson (2001). Several modifications were then implemented to the initial model to bring it closer to psychological and cognitive validity. The second part of the thesis furthers the knowledge available concerning the influence of the time spent attending to a task on streaming. Two deviant detection experiments using triplet stimuli are presented. The first experiment is a follow-up of Thompson, Carlyon and Cusack (2011) and replicated their behavioural findings, showing that the time spent attending to a task enhances streaming, and that deviant detection is easier when one stream is perceived. The ERP results showed double decisions markers indicating that subjects may have made their deviant detection based on the absence of the time delayed deviant and confirmed their decision with its later presence. The second experiment investigated the effect of the time spent attending to the task in presence of a continuity illusion on streaming. It was found that the presence of this illusion prevented streaming in such a way that the pattern of the triplet was strengthened through time instead of separated into two streams, and that the deviant detection was easier the longer the subjects attended to the sound sequence.

Processos de recuperação de memórias são frequentemente investigados através de técnicas de monitoração da atividade cerebral. Na presente tese, é desenvolvido inicialmente um exame sobre a utilização no Brasil de uma ferramenta chamada Potenciais Relacionados ao Evento (PRE). Em seguida, são descritos dois estudos que investigaram processos de recuperação de items neutros associados a contextos emocionais versus contextos neutros. Em ambos os PREs foram extraídos. Através do estudo de revisão sobre PRE no Brasil, constatou-se que esta abordagem de pesquisa ainda é pouco desenvolvida neste país. Através dos outros dois estudos, demonstrou-se a presença de dois efeitos emocionais: um efeito de início rápido (200 ms) e um tardío (iniciando entre 500 e 800 ms). Estes efeitos sugerem que o cérebro responde a items associados a contextos emocionais antes de realizar um processo de recuperação envolvendo a consciência, e indicam que os processos pós-recuperação são modulados pela propriedade emocional dos items. / Memory retrieval processes are frequently investigated by brain monitoring techniques. In the present dissertation, a review on the state of the art of Event-related potentials (ERP) research in Brazil is initially conducted. It is followed by the report of two ERP studies investigating the retrieval processes of neutral items associated to emotional versus neutral contexts. The exam of the Brazilian ERP research demonstrated that this approach still needs to be properly developed in this country. Both ERP studies demonstrated the presence of two main emotional ERP effects: an early onset effect (200 ms) and a late onset effect (onsetting between 500 and 800 ms). These effects suggest that the brain reacts to items associated to emotional contexts before the onset of conscious retrieval processes. They also indicate that post-retrieval processes are modulated by the emotional properties acquired by the items.

Les patients souffrant de schizophrénie présentent des symptômes cliniques ainsi que des déficits cognitifs. Il a été récemment proposé que les déficits de lecture des patients fassent partie de ces déficits. L’objectif de ce travail de thèse était d’évaluer les capacités de reconnaissance visuelle des mots chez les patients souffrant de schizophrénie, au moyen d'une évaluation diagnostique des processus cognitifs dans une approche comportementale et électrophysiologique (enregistrement des potentiels évoqués). Les résultats indiquent une préservation de la spécialisation de l’aire de la forme visuelle des mots pour traiter les mots écrits chez les patients. De plus, les processus cognitifs impliqués dans le traitement orthographique des suites de lettres semblent également préservés. En revanche, les processus cognitifs impliqués dans le traitement phonologique semblent altérés chez les patients souffrant de schizophrénie. / Patients suffering from schizophrenia display clinical symptoms as well as cognitive deficits. Recently, it has been suggested that these patients display, among other things, reading deficits. This doctoral thesis aims to evaluate the abilities of visual word recognition in patients suffering from schizophrenia, using both behavioral and electrophysiological (recording of event related potentials) approaches. The results indicated that the specialization of the visual word form area for processing of written words is preserved for patients. In addition, cognitive processes involved in orthographic processing of letter strings were preserved. By contrast, cognitive processes involved in phonological processing were altered for patients suffering from schizophrenia.

The aim of the current paper is to examine the association between ideology and disgust sensitivity. Studying disgust offers an to assess how judgments have evolved over time due to a “gut” sense of danger. This emotion also plays a role in moral judgment: individuals label moral wrongdoings as disgusting which elicits a specific facial expression. For this reason, disgust has recently been found to be a plausible emotion involved in political decision-making. Studies indicate that liberals and conservatives rely on respective moral foundations that influence their choices. Haidt et al. (2009) argue that liberals’ views on morality are based primarily on harm/care and fairness/reciprocity, whereas conservatives’ views on morality show a more even distribution across the foundations, including those endorsed by liberals, as well as ingroup/loyalty, authority/respect and sanctity. Schnall et al. (2008) suggest a causal relationship between feelings of disgust and moral convictions. People often rely on moral reasoning when they do not have an intuitive response or when their intuition is conflicting. The current study examined this complex relationship by assessing disgust sensitivity while simultaneously manipulating emotional state through the use of emotionally disgusting and neutral pictures. Electroencephalographic (EEG) event related brain potentials (ERPs) were used as the primary index of emotional processing. The results indicated a main effect for electrode site location and for picture image, as expected. Results did not show an interaction between disgust sensitivity and ideology, or any mediating factors, suggesting that there may be no statistically significant differences in disgust sensitivity between liberals and conservatives. These results suggest that the core differences between conservatives and liberals may be exaggerated. Limitations and directions for future research are discussed.

Substance use disorders (SUDs) are a growing concern in today’s society. Substantial research has advanced our understanding of how cognitive control, reward processing, and emotional difficulties may contribute to the development and maintenance of SUDs; however, the impact of affective instability in SUDs has received limited attention. I sought to examine how different dimensions of affective instability interact to increase substance misuse, and to investigate the impact of affective instability and substance use on neural mechanisms of reward and emotion processing. Specifically, I was interested in two event-related potential (ERP) components, the reward positivity and the late positive potential (LPP), which respectively reflect the neural mechanisms of reward and emotion processing. Toward this end, I recorded the ongoing electroencephalogram (EEG) from undergraduate students as they navigated two T-maze tasks in search of rewards. Further, one of the tasks included neutral, pleasant, and unpleasant pictures from the International Affective Picture System (IAPS). Participants also completed several questionnaires pertaining to substance use and personality. A principal components analysis (PCA) revealed a factor related to affective instability, which I named reactivity. This factor significantly predicted increased substance use. Interestingly, individuals reporting higher levels of affective reactivity also displayed a larger reward positivity following stimuli with emotional content. The current study identified a group of high-risk substance users characterized by greater levels of affective reactivity and increased reward processing. It is my hope that these results further elucidate the complexities of SUDs and help to create efficacious, individually-tailored treatment programs for those struggling with SUDs. / Graduate