Face processing deficits appear early in autism and greatly impact subsequent development. In this paper, the N170 component, an event-related brain potential sensitive to face processing, is examined in children with autism and typical development. The N170 amplitude was sensitive to group differences, as children with typical development showed greater differentiation to upright vs. inverted stimuli and faces vs. vehicles than children with autism. The N170 was also delayed in children with autism. The N170 was not a sensitive marker of individual differences in social behavior and autistic symptomology, but the proceeding positive peak, the P1, was a sensitive marker of individual differences in children with typical development. Results suggest that children with autism and children with typical development employ different face processing strategies, even for the basic encoding of a face.

A growing body of research is targeted towards explaining nicotine's numerous and complex effects on selective attention and other forms of attentional processing. However, when and how nicotine modulates attentional processing in the presence of emotional distractors is not well characterized, though potentially quite important given that, relative to nonsmokers, smokers exhibit higher levels of negative affect-related traits and psychological disorders related to negative affect. In this study, electroencephalography (EEG) and event-related potentials (ERPs) were used to better characterize the effects of nicotine replacement therapy (NRT), relative to placebo, on distraction by emotional and smoking-related stimuli across 17 days of abstinence in dependent smokers. It was hypothesized that, relative to placebo, NRT would reduce ERP-indexed distraction (N170) and promote P3b-indexed task-related attention to target digits during a rapidly visual information processing task previously proven to be sensitive to the effects of NRT on attention. It was expected that the effects of valence on N170 to visual distractors and P3b to target digits would be greater in the placebo group than in the NRT group. Results demonstrated that NRT reduced distraction by visual distractors and increased neuroelectric response to target digits relative to placebo patch. Additionally, analyses revealed that the emotional valence of the visual distractors affected P3b response to targets, but did not affect N170-measured distraction during a sustained attention task. Aspects of the effect of NRT and nicotine-abstinence on top-down and bottom-up processes are discussed as possible mechanisms for the effect of nicotine on attention.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Visual snow syndrome is a persistent visual disturbance characterized by rapid flickering dots in the entire visual field. Hypothesized to arise from reduced inhibition of sensory cortex, visual snow has recently been linked to potentiation (enhancement) of the P100, an event-related potential (ERP) component associated with early visual processing. Here, we investigate whether this potentiation in visual snow is specific to visual responses, by comparing ERPs linked to early, bottom-up perceptual versus late, top-down cognitive processes. Specifically, we examined two components, the N170 and P300, associated respectively with rapid face categorization and attentional orienting towards targets. We predicted that if visual snow predominantly reflects diminished inhibition of perceptual areas, there should be stronger potentiation for the earlier perceptual N170 component. ERPs associated with the N170 (Face > House) and P300 (Target > Nontarget) were recorded in a 22 year-old male with a 2-year history of visual snow symptoms and a set of age- and gender-matched controls. Although N170 and P300 responses in all participants showed appropriate face- and target-selectivity, respectively, the visual snow patient demonstrated consistent potentiation relative to controls, particularly for the early N170 response. Bootstrapped estimates of mean amplitude computed within participants similarly revealed larger and more variable ERP amplitudes in the visual snow patient, especially for the N170 component. These results support an early perceptual locus of ERP potentiation in visual snow, further supporting the idea that this condition arises from diminished inhibition of sensory cortices.

Ma thèse porte sur une dimension fondamentale de la structure des groupes sociaux : la hiérarchie. Chez l'être humain, les hiérarchies sociales régissent en profondeur les interactions. Pour naviguer avec succès dans son environnement, il doit être en mesure de repérer précisément les positions hiérarchiques des autres membres de son groupe. Ce travail de thèse vise à caractériser certains mécanismes neuronaux, comportementaux et physiologiques impliqués dans l'analyse d'un indice hiérarchique. Pour préciser la nature du traitement de la hiérarchie, j'ai exploré son influence sur différentes étapes de la perception des visages. Je me suis tout d'abord intéressée au décours temporel du traitement neuronal des visages dans un contexte hiérarchique. Deux études menées en électroencéphalographie m'ont permis d'identifier les potentiels neuronaux et les composants oscillatoires évoqués par la perception de visages associés soit, à un rang hiérarchique établi à l'issue d'une compétition, soit à un statut social induit par la profession. Une étude réalisée ensuite en oculométrie avait pour but de capturer l'influence de la hiérarchie sur des mécanismes fins du contrôle de l'attention visuelle. J'ai étudié à la fois l'exploration visuelle de classements hiérarchiques incluant le participant, et celle de visages associés à des rangs hiérarchiques différents. Enfin, j'ai tenté de déterminer si un signal ou une situation d'asymétrie hiérarchique véhicule une valence émotionnelle et motivationnelle non neutre susceptible d'induire des variations de certains paramètres physiologiques, comme le rythme cardiaque ou la réponse électrodermale / Hierarchy is a key organizational feature of social groups. In order to successfully navigate their social environment, humans must precisely read the hierarchical position of other during social interaction. This present thesis intends to characterize the neural correlates as well as the early physiological and behavioral mechanisms involved in the processing of social rank. The influence of hierarchy was mainly investigated in the context of face perception. To begin, my focus was on the time course of neuronal processing of faces embedded in a hierarchical context. Using eletroencephalography in two studies, it has been possible to identify evoked neuronal potentials and oscillatory components in response to faces varying in hierarchical rank, established through competition or social status induced by profession. The next study used eye-tracking methodology to explore the influence of hierarchy on the subtle mechanisms of visual attention control. I aimed at characterizing the visual scanning pattern of hierarchical rankings (during a competition) and of faces associated with different hierarchical ranks. Finally, I tried to determine if a hierarchical signal or a social asymmetrical situation conveyed an emotional/motivational valence. During face perception and a minimal social interaction, I examined if this particular dimension of hierarchy generated variations of physiological activity, such as heart rate and skin conductance response

Die Blickrichtung und ihre Richtung sind wichtige nonverbale Hinweise für die Etablierung von sozialen Interaktionen und die Wahrnehmung von emotionalen Gesichtsausdrücken bei anderen. Ob der Blick direkt auf den Betrachter gerichtet ist (direkter Blick) oder abgewendet (abgewandter Blick), beeinflusst unsere soziale Aufmerksamkeit und emotionale Reaktionen. Dies deutet darauf hin, dass Emotionen und Blickrichtung informative Werte haben, die sich möglicherweise in frühen oder späteren Stadien der neurokognitiven Verarbeitung interagieren. Trotz theoretischer Grundlage, der geteilten Signal-Hypothese (Adams & Kleck, 2003), gibt es einen Mangel an strukturierten elektrophysiologischen Untersuchungen zu den Wechselwirkungen zwischen Emotionen und Blickrichtung sowie ihren neuronalen Korrelaten und wie sie sich in verschiedenen Bevölkerungsgruppen unterscheiden. Um diese Lücke zu schließen, verwendete diese Doktorarbeit ereigniskorrelierte Hirnpotentiale (ERPs), um die Reaktionen auf emotionale Ausdrücke und Blickrichtung in einem neuen Paradigma zu untersuchen, das statischen und dynamischen Blick mit Gesichtsausdrücken kombiniert. Es wurden drei verschiedene Populationen untersucht. Studie 1 untersuchte in einer normalen Stichprobe die Amplituden der ERP-Komponenten, die durch die erstmalige Präsentation von Gesichtern und nachfolgende Änderungen der Blickrichtung in der Hälfte der Durchgänge ausgelöst wurden. In Studie 2 wurden aufgrund der atypischen Gesichtsverarbeitung und verminderten Reaktionen auf Augenblick beim Autismus die ERPs und Augenbewegungen bei zwei Stichproben von Kindern mit unterschiedlichem Schweregrad ihrer Autismusmerkmale untersucht. In Studie 3 wurde in einer großen Stichprobe die vermutlich erhöhte Sensitivität bei der Emotionsverarbeitung und Reaktion auf Augenblick bei Müttern im postpartalen Zeitraum mit besonderem Fokus auf die Gesichter von Säuglingen untersucht. Zusammenfassend zeigen die Ergebnisse der drei Studien, dass in sozialen Interaktionen die emotionalen Effekte von Gesichtern durch die dynamische Blickrichtung moduliert werden. / The eye gaze and its direction are important and relevant non-verbal cues for the establishment of social interactions and the perception of others’ emotional facial expressions. Gaze direction itself, whether eyes are looking straight at the viewer (direct gaze) or whether they look away (averted gaze), affects our social attention and emotional response. This implies that both emotion and gaze have informational values, which might interact at early or later stages of neurocognitive processing. Despite the suggestion of a theoretical basis for this interaction, the shared signal hypothesis (Adams & Kleck, 2003), there is a lack of structured electrophysiological investigations into the interactions between emotion and gaze and their neural correlates, and how they vary across populations. Addressing this need, the present doctoral dissertation used event-related brain potentials (ERPs) to study responses to emotional expressions and gaze direction in a novel paradigm combining static and dynamic gaze with facial expressions. The N170 and EPN were selected as ERP components believed to reflect gaze perception and reflexive attention, respectively. Three different populations were investigated. Study 1, in a normal sample, investigated the amplitudes of the ERP components elicited by the initial presentation of faces and subsequent changes of gaze direction in half of the trials. In Study 2, based on the atypical face processing and diminished responses to eye gaze in autism, the ERPs and eye movements were examined in two samples of children varying in the severity of their autism traits. In Study 3, In a large sample, I addressed the putatively increased sensitivity in emotion processing and response to eye gaze in mothers during their postpartum period with a particular focus on infant's faces. Taken together, the results from three studies demonstrate that in social interactions, the emotional effects of faces are modulated by dynamic gaze direction.

This thesis explores the causes of the face inversion effect, which is a substantial decrement in performance in recognising facial stimuli when they are presented upside down (Yin,1969). I will provide results from both behavioural and electrophysiological (EEG) experiments to aid in the analysis of this effect. Over the course of six chapters I summarise my work during the four years of my PhD, and propose an explanation of the face inversion effect that is based on the general mechanisms for learning that we also share with other animals. In Chapter 1 I describe and discuss some of the main theories of face inversion. Chapter 2 used behavioural and EEG techniques to test one of the most popular explanations of the face inversion effect proposed by Diamond and Carey (1986). They proposed that it is the disruption of the expertise needed to exploit configural information that leads to the inversion effect. The experiments reported in Chapter 2 were published as in the Proceedings of the 34th annual conference of the Cognitive Science Society. In Chapter 3 I explore other potential causes of the inversion effect confirming that not only configural information is involved, but also single feature orientation information plays an important part in the inversion effect. All the experiments included in Chapter 3 are part of a paper accepted for publication in the Quarterly Journal of Experimental Psychology. Chapter 4 of this thesis went on to attempt to answer the question of whether configural information is really necessary to obtain an inversion effect. All the experiments presented in Chapter 4 are part of a manuscript in preparation for submission to the Quarterly Journal of Experimental Psychology. Chapter 5 includes some of the most innovative experiments from my PhD work. In particular it offers some behavioural and electrophysiological evidence that shows that it is possible to apply an associative approach to face inversion. Chapter 5 is a key component of this thesis because on the one hand it explains the face inversion effect using general mechanisms of perceptual learning (MKM model). On the other hand it also shows that there seems to be something extra needed to explain face recognition entirely. All the experiments included in Chapter 5 were reported in a paper submitted to the Journal of Experimental Psychology; Animal Behaviour Processes. Finally in Chapter 6 I summarise the implications that this work will have for explanations of the face inversion effect and some of the general processes involved in face perception.

The recognition accuracy of emotion in faces varies depending on the discrete emotion being expressed and the location of the stimulus. More specifically, emotion detection performance declines as facial stimuli are presented further out in the periphery. Interestingly, this is not always true for faces depicting happy emotional expressions, which can be associated with maintained levels of detection. The current study examined neurophysiological responses to emotional face discrimination in the periphery. Two event-related potentials (ERPs) that can be sensitive to the perception of emotion in faces, P1 and N170, were examined using EEG data recorded from electrodes at occipitotemporal sites on the scalp. Participants saw a face presented at a 0° angle of eccentricity, at a 10° angle of eccentricity, or at a 20° angle of eccentricity, and responded whether the face was a specific emotion or neutral. Results showed that emotion detection was higher when faces were presented at the center of the display than at 10° or 20° for both happy and angry expressions. Likewise, the voltage amplitude of the N170 component was greater when faces were presented at the center of the display than at 10° or 20°. Further exploration of the data revealed that high intensity expressions were more easily detected at each location and elicited a larger amplitude N170 than low intensity expressions for both emotions. For a peripheral emotion discrimination task like that which was employed in the current study, emotion cues seem to enhance face processing at peripheral locations.

Early-latency theories of emotional processing state that at least coarse monitoring of the emotional valence (a pleasure-displeasure continuum) of facial expressions should be both rapid and highly automated (LeDoux, 1995; Russell, 1980). Research has largely substantiated early-latency differential processing of emotional versus non-emotional facial expressions; however, the effect of valence on early-latency processing of emotional facial expression remains unclear. In an effort to delineate the effects of valence on early-latency emotional facial expression processing, the current investigation compared ERP responses to positive (happy and surprise), neutral, and negative (afraid and sad) basic facial expression photographs as well as to positive (happy-surprise), neutral (afraid-surprise, happy-afraid, happy-sad, sad-surprise), and negative (sad-afraid) morph facial expression photographs during a valence-rating task. Morphing manipulations have been shown to decrease the familiarity of facial patterns and thus preclude any overlearned responses to specific facial codes. Accordingly, it was proposed that morph stimuli would disrupt more detailed emotional identification to reveal a valence response independent of a specific identifiable emotion (Balconi & Lucchiari, 2005; Schweinberger, Burton & Kelly, 1999). ERP results revealed early-latency differentiation between positive, neutral, and negative morph facial expressions approximately 108 milliseconds post-stimulus (P1) within the right electrode cluster; negative morph facial expressions continued to elicit significantly smaller ERP amplitudes than other valence categories approximately 164 milliseconds post-stimulus (N170). Consistent with previous imaging research on emotional facial expression processing, source localization revealed substantial dipole activation within regions of the mesolimbic dopamine system. Thus, these findings confirm rapid valence processing of facial expressions and suggest that negative valence processing may continue to modulate subsequent structural facial processing.

The ability to recognise an individual's affective state from their facial expression is crucial to human social interaction. However, understanding of facial expression recognition processes is limited because mounting evidence has revealed important differences between posed and genuine facial expressions of emotion. Most previous studies of facial expression recognition have used only posed or simulated facial expressions as stimuli, but posed expressions do not reflect underlying affective state unlike genuine expressions. The current study compared behavioural responses and Evoked Response Potentials (ERPs) to neutral expressions, posed smiles and genuine smiles, during three different tasks. In the first task, no behavioural judgment was required, whereas participants were required to judge whether the person was showing happiness in the second task or feeling happiness in the third task. Behavioural results indicated that participants exhibited a high degree of sensitivity in detecting the emotional state of expressions. Genuine smiles were usually labelled as both showing and feeling happiness, but posed smiles were far less likely to be labelled as feeling happiness than as showing happiness. Analysis of P1 and N170 components, and later orbitofrontal activity, revealed differential activity levels in response to neutral expressions as compared to posed and genuine smiles. This differential activity occurred as early as 135ms at occipital locations and from 450ms at orbitofrontal locations. There were significant interactions between participant behavioural sensitivity to emotional state and P1 and N170 amplitudes. However, no significant difference in ERP activity between posed smiles and genuine smiles was observed until 850ms at orbitofrontal locations. An additional finding was greater right temporal and left orbitofrontal activation suggesting hemispheric asymmetry of facial expression processing systems.