Adults perceive basic emotional facial expressions as discrete categories using categorical perception. Within categorical perception, discrimination of facial emotional expressions is better for between category faces than within category faces. In this thesis, I examined the developmental trajectory of categorical perception in early childhood. I also examined the relationship between sensitivity to physical differences in facial emotional expressions and the use of emotion labels in toddlers. In Chapter 2, I found that infants before 12-months failed to discriminate between category faces along a happy-sad continuum. In contrast, evidence suggest that 9- and 12-month old infants categorically perceived faces along a happy-angry continuum. These findings suggest that categorical perception may not develop concurrently for all emotions. In Chapter 3, I found that toddlers by 26-months of age categorically perceived faces along a happy-sad continuum. These results highlight the long developmental trajectory of categorical perception of facial emotional expressions across early childhood. In Chapter 4, I found a relationship between perceptual sensitivity to physical differences between happy and sad faces, and the emotion vocabulary size in 26-month-olds. This relationship suggests that learning about emotions may utilize information from multiple domains, and that learning in one domain may influence the development of another. The perception of facial emotional expressions is an essential component of early social emotional development. Categorical perception is a mechanism that aids in organizing complex social information from faces into actionable categories. The research in this thesis advances our understanding of early social perceptual development and the process that allow us to successfully navigate in the social world. / Dissertation / Doctor of Philosophy (PhD) / Humans are experts at reading faces. Specifically, they are capable of interpreting complex social information from faces, including emotions, and using this information to navigate social situations. In order to organize facial emotional information, humans use a mechanism called categorical perception to quickly and efficiently sort facial emotional information into discrete categories. Inferences can be made about members within a category, which aids in the prediction and production appropriate behaviours. However, there has been limited research into the development of categorical perception in early childhood. The key goal of this thesis was to develop infant and toddler appropriate methodologies that capture the development categorical perception. In this thesis, I found that categorical perception does not develop uniformly across all ages and between different emotions. Results suggest that perceptual sensitivity to differences in facial emotional expression may be influenced by the use of emotion labels, or vice versa.

This study explored the relationship between gaze anxiety and the perception of facial expressions. The literature suggests that individuals experiencing Social Anxiety Disorder (SAD) might have a fear of making direct eye contact, and that these individuals also demonstrate a hypervigilance towards the eye region. It was thought that this increased anxiety concerning eye contact might be related to the tendency of socially anxious individuals to mislabel emotion in the faces of onlookers. A better understanding of the cognitive biases common to SAD could lead to more efficient intervention and assessment methods. In the present study, the Depression Anxiety Stress Scale-21 (DASS-21) and the Social Phobia and Anxiety Inventory-23 (SPAI-23) were used to measure social anxiety, depression, and overall distress. These forms allowed us to separate participants who reported high socially anxious and depressive traits from those in the normal range. We then compared anxiety concerning mutual eye contact as measured by the Gaze Anxiety Rating Scale (GARS) to performance on a facial recognition task. Performance was measured as recognition accuracy and average perceived intensity of onlooker expression on a scale of 1-5. A linear regression analysis revealed that higher GARS scores were related to higher perceived intensity of emotion by socially anxious individuals. An exploratory correlation analysis also revealed that higher gaze anxiety was related to lower accuracy at identifying neutral emotions and higher accuracy at identifying angry emotions. While past research has demonstrated these same biases by socially anxious individuals, gaze anxiety had not been explored extensively. Future research should investigate gaze anxiety’s role as a moderating variable.

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<p>Older adults tend to show overall recognition deficits and qualitatively different patterns in the particular expressions that are most difficult to identify (Ruffman et al., 2008). In the current study, 23 younger (18-33 years old) and 23 older (60-80 years old) adults performed a 4AFC (angry, fearful, happy, sad) facial expression categorization task varying orientation (upright/inverted) and stimulus duration (100, 500, 1000 ms). For both groups, happiness was the easiest expression to identify and fear and sadness were the most difficult. Compared to younger adults, older adults were more affected by stimulus orientation, and generally benefit less from increased stimulus duration. For upright faces, there was no age difference in response accuracy but response latency was longer in older subjects. For inverted faces, older adults showed lower accuracy and longer latencies for expressions of anger, fear, and sadness. Recognition of inverted happy faces was spared in older adults for accuracy, but not response latency. These findings could not be explained by impaired detection sensitivity, as no systematic age differences were found for perceived intensity ratings. Finally, the expressions that were most to least difficult to identify was the same in each age group at both orientations. Overall, these results suggest that older individuals process expressive faces in a qualitatively similar way to their younger counterparts, but are less efficient at extracting the diagnostic information.</p> / Master of Science (MSc)

<p>There is strong agreement among adults both within and across cultures as to which faces are attractive (Langlois et al., 2000), and these perceptions can affect social interactions via the ‘beauty is good’ stereotype (Dion, Berscheid, & Walster, 1972). Adults perceive faces that are symmetrical to be more attractive than faces that are less symmetrical (Perrett et al., 1999), and faces that approximate the population average to be more attractive than most other faces (Langlois & Roggman, 1990). I examined the development of the influence of symmetry and averageness on children’s judgments of facial attractiveness in the faces of children and adults. In the work presented in chapters 2 and 3, I presented children and adults with pairs of faces that had been transformed to be more symmetrical and less symmetrical (chapter 2) or closer and farther from their group average (chapter 3). On each trial, participants selected which face was more attractive from the pair. I found that symmetry did not influence 5-year-olds’ judgments of attractiveness, but it did influence 9-year-olds’ judgments of attractiveness although to a lesser extent than those of adults. I additionally found that averageness strongly influenced 5-yearolds’ attractiveness judgments, and the strength of the preference increased from age 5 to 9, and from age 9 to adulthood. These findings are the first demonstrations that symmetry and averageness influence attractiveness judgments prior to adolescence, and that they influence attractiveness judgments in children’s faces. To assess whether natural differences in face experience can affect how strongly averageness is preferred in different face categories, I tested children attending single-sex schools and expected averageness to influence attractiveness judgments more strongly in same-sex than opposite-sex faces of their own age (chapter 4). I did not find that pattern of results. Averageness might influence attractiveness judgments regardless of the age and sex of face because a minimum level of face experience could be adequate for attractiveness judgments based on a prototype and/or because of similarities among averages of different ages and sexes. Together, the findings of this thesis demonstrate that children assess facial attractiveness based on some of the same dimensions as do adults, but that children are more tolerant of deviations from averageness and symmetry. Developmental changes might reflect the refinement of a face prototype as experience with faces increase, increased visual sensitivity as the visual system develops, and/or increased salience of cues for mate choice after puberty.</p> / Doctor of Science (PhD)

Perceptual learning occurs because observers become more sensitive to informative aspects of the stimuli. Learning the informative aspects of one stimulus set does not transfer to another stimulus set of the same class. In this dissertation, the argument will be made that if observers learn how to discover informative aspects, learning will be more generalizable. However, discovery requires that the informative aspects are not easily apparent. To this end, stimulus orientation structure can be manipulated to contain informative structure in one orientation band, and non-informative structure in the other orientation band. Such a manipulation was inspired by research on face perception: Faces are best identified when decisions are based more on the horizontal relative to the vertical facial structure. Hence, the first three chapters focus on understanding the horizontal bias during face identification, and the final two chapters introduce a novel stimulus set for which horizontal bias may be learned. Chapter 2 identifies a neural marker of horizontal bias that is correlated with face identification accuracy, suggesting that we can predict how well observers identify faces based on their neural sensitivity to horizontal relative to vertical structure. Chapter 3 shows that when face identification accuracy declines due to healthy ageing, so too do behavioural and neural horizontal bias, but Chapter 4 shows that perceptual learning can increase horizontal bias in healthy older adults. Chapter 5 uses texture stimuli and shows that observers can learn to discover informative horizontal structure embedded in uninformative vertical structure. Chapter 6 extends these findings to show that adequate practice results in learning that generalizes to novel textures for which the orientation-selective processing is relevant. The results presented inform our understanding of the neural representations associated with orientation-selective processing, and suggest that observers can learn to discover informative structure conveyed by a particular orientation band. / Thesis / Doctor of Philosophy (PhD)

Many non-human animal species use colour to signal dominance, condition or reproductive status. These signals have not previously been noted in humans. This thesis investigates the effects of skin colouration and pigmentation on the apparent health of human faces. Section 2 showed that individuals with increased fruit and vegetable and carotenoid consumption have yellower skin (Study 1) due to increased carotenoid pigmentation in the skin (Study 2). In Section 3, participants enhanced the redness, yellowness and lightness of the skin portions of colour-calibrated facial photographs to optimise healthy appearance. This suggests roles for blood (red) and carotenoid/melanin (yellow) colouration in providing perceptible cues to health. The contrast between lips and facial skin colour was not found to affect the apparent health of the faces, except in the b* (yellowness) axis, where enhanced facial yellowness caused an apparent blue tint to the lips. In Section 4 participants enhanced empirically-derived oxygenated blood colour more than deoxygenated blood colour to optimise healthy appearance. In two-dimensional trials, when both blood colour axes could be manipulated simultaneously, deoxygenated blood colour was removed and replaced with oxygenated blood colour. Oxygenated blood colouration appears to drive the preference for redness in faces. In Section 5 participants increased carotenoid colour significantly more than they increased melanin colour in both single-axis and two-dimensional trials. Carotenoid colour appears to drive the preference for yellowness in faces. In a cross-cultural study (Section 6), preferences for red and yellow in faces were unaffected by face or participant ethnicity, while African participants lightened faces more than UK participants. A preference for more redness in East Asian faces was explained by this group’s lower initial redness. The thesis concludes that pigments that provide sexually-selected signals of quality in many non-human animal species – carotenoids and oxygenated blood - also provide perceptible cues to health in human faces.

Les stimuli naturels projetés sur nos rétines nous fournissent de l’information visuelle riche. Cette information varie le long de propriétés de « bas niveau » telles que la luminance, le contraste, et les fréquences spatiales. Alors qu’une partie de cette information atteint notre conscience, une autre partie est traitée dans le cerveau sans que nous en soyons conscients. Les propriétés de l’information influençant l’activité cérébrale et le comportement de manière consciente versus non-consciente demeurent toutefois peu connues. Cette question a été examinée dans les deux derniers articles de la présente thèse, en exploitant les techniques psychophysiques développées dans les deux premiers articles. Le premier article présente la boîte à outils SHINE (spectrum, histogram, and intensity normalization and equalization), développée afin de permettre le contrôle des propriétés de bas niveau de l'image dans MATLAB. Le deuxième article décrit et valide la technique dite des bulles fréquentielles, qui a été utilisée tout au long des études de cette thèse pour révéler les fréquences spatiales utilisées dans diverses tâches de perception des visages. Cette technique offre les avantages d’une haute résolution au niveau des fréquences spatiales ainsi que d’un faible biais expérimental. Le troisième et le quatrième article portent sur le traitement des fréquences spatiales en fonction de la conscience. Dans le premier cas, la méthode des bulles fréquentielles a été utilisée avec l'amorçage par répétition masquée dans le but d’identifier les fréquences spatiales corrélées avec les réponses comportementales des observateurs lors de la perception du genre de visages présentés de façon consciente versus non-consciente. Les résultats montrent que les mêmes fréquences spatiales influencent de façon significative les temps de réponse dans les deux conditions de conscience, mais dans des sens opposés. Dans le dernier article, la méthode des bulles fréquentielles a été combinée à des enregistrements intracrâniens et au Continuous Flash Suppression (Tsuchiya & Koch, 2005), dans le but de cartographier les fréquences spatiales qui modulent l'activation de structures spécifiques du cerveau (l'insula et l'amygdale) lors de la perception consciente versus non-consciente des expressions faciales émotionnelles. Dans les deux régions, les résultats montrent que la perception non-consciente s'effectue plus rapidement et s’appuie davantage sur les basses fréquences spatiales que la perception consciente. La contribution de cette thèse est donc double. D’une part, des contributions méthodologiques à la recherche en perception visuelle sont apportées par l'introduction de la boîte à outils SHINE ainsi que de la technique des bulles fréquentielles. D’autre part, des indications sur les « corrélats de la conscience » sont fournies à l’aide de deux approches différentes. / Natural stimuli impinging on our retinas provide us with a wealth of visual information. This information varies along “low-level” features, such as luminance, contrast, and spatial frequency (SF). Whereas some of this information reaches our awareness, some of it is processed in the brain without us ever becoming aware of it (i.e., non-consciously). A remaining question is precisely which SFs influence brain activation and behavior consciously vs. non-consciously. The aim of this thesis was to address this question using state-of the-art psychophysical techniques. The first article introduces the SHINE (spectrum, histogram, and intensity normalization and equalization) toolbox for controlling low-level image properties in MATLAB. The second article describes and validates the SF Bubbles technique, which was used throughout the studies in this thesis to map SF tuning for various face perception tasks with a high SF resolution and low experimental bias. The third and fourth articles focus on SF processing as a function of awareness. In the former, SF Bubbles was employed together with repetition priming and masking to investigate which SFs are correlated with observers’ behavioral responses during conscious vs. non-conscious face-gender perception. The results show that the same SFs significantly influenced response times in both prime awareness conditions but, surprisingly, in opposite ways. In the latter, SF Bubbles was combined with intracranial recordings from awake human patients and Continuous Flash Suppression (Tsuchiya & Koch, 2005). This allowed us to map the SFs that modulate activation in specific brain structures (the insula and the amygdala) during the conscious vs. non-conscious perception of emotional facial expressions. The results for both regions demonstrate that non-conscious perception relied on low SFs more and was faster than conscious perception. The contribution made in this thesis is thus two-fold: methodological contributions to visual perception research are made by introducing the SHINE toolbox and the SF Bubbles technique, and insights into the “informational correlates” of consciousness are provided from two different angles.

A técnica de campo visual dividido foi utilizada na análise dos padrões de assimetria cerebral para a percepção de expressões faciais de valência positiva e negativa. Oitenta universitários destros (65 mulheres, 15 homens) foram distribuídos em cinco grupos experimentais com o objetivo de se investigar separadamente a percepção de expressões de alegria, medo, surpresa, tristeza e da face neutra. Em cada apresentação de estímulo, uma face alvo e uma face distratora eram apresentadas à direita ou à esquerda de um ponto de fixação localizado no centro da tela do computador. O tempo de apresentação dos estímulos foi de 150 ms e os participantes tiveram que determinar o lado (esquerdo ou direito) em que havia sido apresentada a face alvo, utilizando um mouse para responderem aos estímulos. As análises estatísticas de tempo de reação e erros de julgamento indicaram não haver diferenças entre o desempenho de homens e mulheres na tarefa experimental. Expressões faciais de alegria e medo foram identificadas mais rapidamente quando apresentadas no campo visual esquerdo, indicando uma possível vantagem do hemisfério direito na percepção destas emoções. Menores tempos de reação e erros de julgamento foram observados para as condições de pareamento em que faces emocionais foram apresentadas no campo visual esquerdo e faces neutras no campo visual direito. A análise dos pareamentos entre faces indicou que faces neutras e de alegria são percebidas mais rapidamente e com maior acerto que faces de medo e tristeza. Embora não tenha havido uma vantagem do hemisfério direito para a percepção de todas as expressões faciais, os resultados deste estudo tendem a concordar com a hipótese do hemisfério direito para o processamento emocional. / The divided visual field technique was used to analize the patterns of brain asymmetry in the perception of positive and negative facial expressions. Eighty undergraduate students (65 female, 15 male) were distributed in five experimental groups in order to investigate separately the perception of expressions of happiness, surprise, fear, sadness, and neutral. In each trial, a target and a distractor expression were presented in a computer screen during 150 ms and participants had to determine the side (left or right) on which the target expression was presented using a mouse to respond to the stimuli. Time reaction and judgment errors analysis showed no differences between men and womens performance in experimental task. Results indicated that expressions of happiness and fear were identified faster when presented on the left visual field, suggesting an advantage of the right hemisphere in the perception of these expressions. Fewer judgment errors and faster reaction times were observed for the matching condition in which emotional faces were presented on the left visual field and neutral faces on the right visual field. Analysis of the pairs of faces indicated that neutral and happy faces were perceived faster and more accurately than faces of fear and happiness. Although an advantage of the right hemisphere was not occurred for the perception of all expressions, results tend to support the right hemisphere hypothesis for emotional processing.