The Role of Experience in the Organization and Refinement of Face Space

Adults code faces in reference to category-specific norms that represent the different face categories encountered in the environment (e.g., race, age). Reliance on such norm-based coding appears to aid recognition, but few studies have examined the development of separable prototypes and the way in which experience influences the refinement of the coding dimensions associated with different face categories. The present dissertation was thus designed to investigate the organization and refinement of face space and the role of experience in shaping sensitivity to its underlying dimensions. In Study 1, I demonstrated that face space is organized with regard to norms that reflect face categories that are both visually and socially distinct. These results provide an indication of the types of category-specific prototypes that can conceivably exist in face space. Study 2 was designed to investigate whether children rely on category-specific prototypes and the extent to which experience facilitates the development of separable norms. I demonstrated that unlike adults and older children, 5-year-olds rely on a relatively undifferentiated face space, even for categories with which they receive ample experience. These results suggest that the dimensions of face space undergo significant refinement throughout childhood; 5 years of experience with a face category is not sufficient to facilitate the development of separable norms. In Studies 3 through 5, I examined how early and continuous exposure to young adult faces may optimize the face processing system for the dimensions of young relative to older adult faces. In Study 3, I found evidence for a young adult bias in attentional allocation among young and older adults. However, whereas young adults showed an own-age recognition advantage, older adults exhibited comparable recognition for young and older faces. These results suggest that despite the significant experience that older adults have with older faces, the early and continuous exposure they received with young faces continues to influence their recognition, perhaps because face space is optimized for young faces. In Studies 4 and 5, I examined whether sensitivity to deviations from the norm is superior for young relative to older adult faces. I used normality/attractiveness judgments as a measure of this sensitivity; to examine whether biases were specific to norm-based coding, I asked participants to discriminate between the same faces. Both young and older adults were more accurate when tested with young relative to older faces—but only when judging normality. Like adults, 3- and 7-year-olds were more accurate in judging the attractiveness of young faces; however, unlike adults, this bias extended to the discrimination task. Thus by 3 years of age children are more sensitive to differences among young relative to older faces, suggesting that young children's perceptual system is more finely tuned for young than older adult faces. Collectively, the results of this dissertation help elucidate the development of category-specific norms and clarify the role of experience in shaping sensitivity to the dimensions of face space.

La protection des mineurs face à la cyberpédopornographie : étude comparée entre le droit criminel canadien et français

Réalisé en cotutelle avec l'Université de Paris-sud XI, France.

Visual information processing during conscious and non-conscious face perception

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.

New stimuli-responsive block random copolymers and their aggregation

Les polymères sensibles à des stimuli ont été largement étudiés ces dernières années notamment en vue d’applications biomédicales. Ceux-ci ont la capacité de changer leurs propriétés de solubilité face à des variations de pH ou de température. Le but de cette thèse concerne la synthèse et l’étude de nouveaux diblocs composés de deux copolymères aléatoires. Les polymères ont été obtenus par polymérisation radicalaire contrôlée du type RAFT (reversible addition-fragmentation chain-transfer). Les polymères à bloc sont formés de monomères de méthacrylates et/ou d’acrylamides dont les polymères sont reconnus comme thermosensibles et sensible au pH. Premièrement, les copolymères à bloc aléatoires du type AnBm-b-ApBq ont été synthétisés à partir de N-n-propylacrylamide (nPA) et de N-ethylacrylamide (EA), respectivement A et B, par polymérisation RAFT. La cinétique de copolymérisation des poly(nPAx-co-EA1-x)-block-poly(nPAy-co-EA1-y) et leur composition ont été étudiées afin de caractériser et évaluer les propriétés physico-chimiques des copolymères à bloc aléatoires avec un faible indice de polydispersité . Leurs caractères thermosensibles ont été étudiés en solution aqueuse par spectroscopie UV-Vis, turbidimétrie et analyse de la diffusion dynamique de la lumière (DLS). Les points de trouble (CP) observés des blocs individuels et des copolymères formés démontrent des phases de transitions bien définies lors de la chauffe. Un grand nombre de macromolécules naturels démontrent des réponses aux stimuli externes tels que le pH et la température. Aussi, un troisième monomère, 2-diethylaminoethyl methacrylate (DEAEMA), a été ajouté à la synthèse pour former des copolymères à bloc , sous la forme AnBm-b-ApCq , et qui offre une double réponse (pH et température), modulable en solution. Ce type de polymère, aux multiples stimuli, de la forme poly(nPAx-co-DEAEMA1-x)-block-poly(nPAy-co-EA1-y), a lui aussi été synthétisé par polymérisation RAFT. Les résultats indiquent des copolymères à bloc aléatoires aux propriétés physico-chimiques différentes des premiers diblocs, notamment leur solubilité face aux variations de pH et de température. Enfin, le changement d’hydrophobie des copolymères a été étudié en faisant varier la longueur des séquences des blocs. Il est reconnu que la longueur relative des blocs affecte les mécanismes d’agrégation d’un copolymère amphiphile. Ainsi avec différents stimuli de pH et/ou de température, les expériences effectuées sur des copolymères à blocaléatoires de différentes longueurs montrent des comportements d’agrégation intéressants, évoluant sous différentes formes micellaires, d’agrégats et de vésicules.

La vulnérabilité face au risque cyclonique : le cas du wilayat Bawshar en Oman

L’objectif de ce mémoire est de réaliser une étude descriptive et évaluative de la vulnérabilité du wilayat Bawshar (district du gouvernorat Mascate, capitale du Sultanat d’Oman), face au risque cyclonique et ce, dans le but de promouvoir la prévention et l’adaptation. À partir des diverses méthodes d’analyse de la vulnérabilité, présentées dans le cadre théorique, nous souhaitons développer une méthode basée sur la prémisse que la vulnérabilité est un système composé de plusieurs facteurs. Cette méthode sera ensuite adaptée au contexte du wilayat Bawshar en lien avec le risque cyclonique. Cette approche est réalisée autour de trois dimensions de la vulnérabilité : physique, sociale et institutionnelle. À la suite de l’application à notre cas d'étude des différentes théories et méthodes analytiques, réalisée grâce à une analyse qualitative et quantitative, générée par une recherche documentaire, des entrevues semi-dirigées, des données statistiques et géomatiques, une observation directe du terrain d’étude ainsi qu’un sondage, voici les importants résultats que nous avons obtenus : les cyclones affectant le gouvernorat de Mascate génèrent d’importants dommages tels que les pertes de vies humaines, la destruction des maisons et des principaux réseaux de transport, ainsi que d’autres perturbations, ceci dû principalement aux inondations émanant des cyclones. Cet endommagement s’explique par la combinaison et l’interaction de plusieurs facteurs tels que les changements océanographiques et atmosphériques affectant le pays ainsi que la topographie et l’hydrologie du site. Les facteurs tels que l’étalement urbain, l’urbanisation de zones à risques, l’explosion démographique, la non diversification de l’économie ainsi que les conditions socio-économiques amplifient la vulnérabilité face au risque cyclonique. Toutefois d’autres facteurs et changements réalisés par le Sultanat d’Oman dans les dernières années diminuent la vulnérabilité de sa population et réduisent l’endommagement à la suite de tels aléas. Parmi eux, nous retrouvons le développement que le pays a soutenu depuis 1970 dans plusieurs secteurs tels que la santé, l’éducation, les infrastructures et l’instauration de politiques de développement durable visant à diversifier l’économie. Depuis le passage des cyclones Gonu et Phet au Sultanat d’Oman, la gestion des risques est au centre même des priorités gouvernementales.

Individuals' (re-)action in the face of global warming

Climate change remains a major challenge for today’s and future societies due to its immense impacts on human lives and the natural environment. This thesis investigates the extent to which individuals are willing and prepared to voluntarily contribute to climate protection and to adjust to new climatic conditions in order to cope with the consequences of climate change and reduce the severity of potential negative impacts. The thesis thereby combines research in the fields of the private provision of environmental public goods and adaptation to climate change, which is still widely unconnected in the existing literature. The six contributions of this thesis mainly focus on microeconometric analyses using data from international surveys in China, Germany, and the USA. The main findings are: (i) A substantial share of individuals is willing to voluntarily contribute to climate protection and to adapt to climatic change. The engagement in both strategies is positively interrelated at the individual level and the analyses reveal hardly any evidence that adaptation activities crowd out individuals’ incentives to engage in climate protection. (ii) The main determinants of individuals’ adaptation activities seem to be the subjective risk perception as well as socio-economic and socio-demographic characteristics like age, gender, education, and income, while their climate protection efforts are found to be broadly motivated by financial advantages from these activities and additional immaterial benefits. (iii) The empirical findings also suggest a significantly positive relationship between certain climate protection activities. Substitutions are found to occur merely if one measure is perceived to be more effective in providing climate protection or if individuals have high environmental preferences. (iv) This thesis further reveals a common understanding of a (normatively) fair burden-sharing in international climate policy across citizens in China, Germany, and the USA. The highest preferences are found for the accountability principle.

Conditions for Viewpoint Dependent Face Recognition

Poggio and Vetter (1992) showed that learning one view of a bilaterally symmetric object could be sufficient for its recognition, if this view allows the computation of a symmetric, "virtual," view. Faces are roughly bilaterally symmetric objects. Learning a side-view--which always has a symmetric view--should allow for better generalization performances than learning the frontal view. Two psychophysical experiments tested these predictions. Stimuli were views of shaded 3D models of laser-scanned faces. The first experiment tested whether a particular view of a face was canonical. The second experiment tested which single views of a face give rise to best generalization performances. The results were compatible with the symmetry hypothesis: Learning a side view allowed better generalization performances than learning the frontal view.

Relative Contributions of Internal and External Features to Face Recognition

The central challenge in face recognition lies in understanding the role different facial features play in our judgments of identity. Notable in this regard are the relative contributions of the internal (eyes, nose and mouth) and external (hair and jaw-line) features. Past studies that have investigated this issue have typically used high-resolution images or good-quality line drawings as facial stimuli. The results obtained are therefore most relevant for understanding the identification of faces at close range. However, given that real-world viewing conditions are rarely optimal, it is also important to know how image degradations, such as loss of resolution caused by large viewing distances, influence our ability to use internal and external features. Here, we report experiments designed to address this issue. Our data characterize how the relative contributions of internal and external features change as a function of image resolution. While we replicated results of previous studies that have shown internal features of familiar faces to be more useful for recognition than external features at high resolution, we found that the two feature sets reverse in importance as resolution decreases. These results suggest that the visual system uses a highly non-linear cue-fusion strategy in combining internal and external features along the dimension of image resolution and that the configural cues that relate the two feature sets play an important role in judgments of facial identity.

Stimuli-responsive Novel Amphiphilic Polymers for Chemical and Biomedical Applications

Amphiphilic polymers are a class of polymers that self-assemble into different types of microstructure, depending on the solvent environment and external stimuli. Self assembly structures can exist in many different forms, such as spherical micelles, rod-like micelles, bi-layers, vesicles, bi-continuous structure etc. Most biological systems are basically comprised of many of these organised structures arranged in an intelligent manner, which impart functions and life to the system. We have adopted the atom transfer radical polymerization (ATRP) technique to synthesize various types of block copolymer systems that self-assemble into different microstructure when subject to an external stimuli, such as pH or temperature. The systems that we have studied are: (1) pH responsive fullerene (C60) containing poly(methacrylic acid) (PMAA-b-C60); (2) pH and temperature responsive fullerene containing poly[2-(dimethylamino)ethyl methacrylate] (C₆₀-b-PDMAEMA); (3) other responsive water-soluble fullerene systems. By varying temperature, pH and salt concentration, different types microstructure can be produced. In the presence of inorganic salts, fractal patterns at nano- to microscopic dimension were observed for negatively charged PMAA-b-C60, while such structure was not observed for positively charged PDMAEMA-b-C60. We demonstrated that negatively charged fullerene containing polymeric systems can serve as excellent nano-templates for the controlled growth of inorganic crystals at the nano- to micrometer length scale and the possible mechanism was proposed. The physical properties and the characteristics of their self-assembly properties will be discussed, and their implications to chemical and biomedical applications will be highlighted.

Differential regulation of Krüppel-like factor family transcription factor expression in neonatal rat cardiac myocytes: effects of endothelin-1, oxidative stress and cytokines

Krüppel-like transcription factors (Klfs) modulate fundamental cell processes. Cardiac myocytes are terminally-differentiated, but hypertrophy in response to stimuli such as endothelin-1. H2O2 or cytokines promote myocyte apoptosis. Microarray studies of neonatal rat myocytes identified several Klfs as endothelin-1-responsive genes. We used quantitative PCR for further analysis of Klf expression in neonatal rat myocytes. In response to endothelin-1, Klf2 mRNA expression was rapidly increased ( approximately 9-fold; 15-30 min) with later increases in expression of Klf4 and Klf6 ( approximately 5-fold; 30-60 min). All were regulated as immediate early genes (cycloheximide did not inhibit the increases in expression). Klf5 expression was increased at 1-2 h ( approximately 13-fold) as a second phase response (cycloheximide inhibited the increase). These increases were transient and attenuated by U0126. H2O2 increased expression of Klf2, Klf4 and Klf6, but interleukin-1beta or tumor necrosis factor alpha downregulated Klf2 expression with no effect on Klf4 or Klf6. Of the Klfs which repress transcription, endothelin-1 rapidly downregulated expression of Klf3, Klf11 and Klf15. The dynamic regulation of expression of multiple Klf family members in cardiac myocytes suggests that, as a family, they are actively involved in regulating phenotypic responses (hypertrophy and apoptosis) to extracellular stimuli.

Characterizing typographic expertise: do we process typefaces like faces?

Studies of face recognition and discrimination provide a rich source of data and debate on the nature of their processing, in particular through using inverted faces. This study draws parallels between the features of typefaces and faces, as letters share a basic configuration, regardless of typeface, that could be seen as similar to faces. Typeface discrimination is compared using paragraphs of upright letters and inverted letters at three viewing durations. Based on previously reported effects of expertise, the prediction that designers would be less accurate when letters are inverted, whereas nondesigners would have similar performance in both orientations, was confirmed. A proposal is made as to which spatial relations between typeface components constitute holistic and configural processing, posited as the basis for better discrimination of the typefaces of upright letters. Such processing may characterize designers’ perceptual abilities, acquired through training.

Visual search for basic emotional expressions in autism; impaired processing of anger, fear and sadness, but a typical happy face advantage

Facial expression recognition was investigated in 20 males with high functioning autism (HFA) or Asperger syndrome (AS), compared to typically developing individuals matched for chronological age (TD CA group) and verbal and non-verbal ability (TD V/NV group). This was the first study to employ a visual search, “face in the crowd” paradigm with a HFA/AS group, which explored responses to numerous facial expressions using real-face stimuli. Results showed slower response times for processing fear, anger and sad expressions in the HFA/AS group, relative to the TD CA group, but not the TD V/NV group. Reponses to happy, disgust and surprise expressions showed no group differences. Results are discussed with reference to the amygdala theory of autism.

Video stimuli reduce object-directed imitation accuracy: a novel two-person motion-tracking approach

Imitation is an important form of social behavior, and research has aimed to discover and explain the neural and kinematic aspects of imitation. However, much of this research has featured single participants imitating in response to pre-recorded video stimuli. This is in spite of findings that show reduced neural activation to video vs. real life movement stimuli, particularly in the motor cortex. We investigated the degree to which video stimuli may affect the imitation process using a novel motion tracking paradigm with high spatial and temporal resolution. We recorded 14 positions on the hands, arms, and heads of two individuals in an imitation experiment. One individual freely moved within given parameters (moving balls across a series of pegs) and a second participant imitated. This task was performed with either simple (one ball) or complex (three balls) movement difficulty, and either face-to-face or via a live video projection. After an exploratory analysis, three dependent variables were chosen for examination: 3D grip position, joint angles in the arm, and grip aperture. A cross-correlation and multivariate analysis revealed that object-directed imitation task accuracy (as represented by grip position) was reduced in video compared to face-to-face feedback, and in complex compared to simple difficulty. This was most prevalent in the left-right and forward-back motions, relevant to the imitator sitting face-to-face with the actor or with a live projected video of the same actor. The results suggest that for tasks which require object-directed imitation, video stimuli may not be an ecologically valid way to present task materials. However, no similar effects were found in the joint angle and grip aperture variables, suggesting that there are limits to the influence of video stimuli on imitation. The implications of these results are discussed with regards to previous findings, and with suggestions for future experimentation.

Microbial Recognition Via Toll-Like Receptor-Dependent and -Independent Pathways Determines the Cytokine Response of Murine Dendritic Cell Subsets to CD40 Triggering

Dendritic cells (DC) can produce Th-polarizing cytokines and direct the class of the adaptive immune response. Microbial stimuli, cytokines, chemokines, and T cell-derived signals all have been shown to trigger cytokine synthesis by DC, but it remains unclear whether these signals are functionally equivalent and whether they determine the nature of the cytokine produced or simply initiate a preprogrammed pattern of cytokine production, which may be DC subtype specific. Here, we demonstrate that microbial and T cell-derived stimuli can synergize to induce production of high levels of IL-12 p70 or IL-10 by individual murine DC subsets but that the choice of cytokine is dictated by the microbial pattern recognition receptor engaged. We show that bacterial components such as CpG-containing DNA or extracts from Mycobacterium tuberculosis predispose CD8alpha(+) and CD8alpha(-)CD4(-) DC to make IL-12 p70. In contrast, exposure of CD8alpha(+), CD4(+) and CD8alpha(-)CD4(-) DC to heat-killed yeasts leads to production of IL-10. In both cases, secretion of high levels of cytokine requires a second signal from T cells, which can be replaced by CD40 ligand. Consistent with their differential effects on cytokine production, extracts from M. tuberculosis promote IL-12 production primarily via Toll-like receptor 2 and an MyD88-dependent pathway, whereas heat-killed yeasts activate DC via a Toll-like receptor 2-, MyD88-, and Toll/IL-1R domain containing protein-independent pathway. These results show that T cell feedback amplifies innate signals for cytokine production by DC and suggest that pattern recognition rather than ontogeny determines the production of cytokines by individual DC subsets.

Activation of glycoprotein VI (GPVI) and C-type lectin-like receptor-2 (CLEC-2) underlies platelet activation by diesel exhaust particles and other charged/hydrophobic ligands

Platelets are activated by a range of stimuli that share little or no resemblance in structure to each other or to recognized ligands, including diesel exhaust particles (DEP), small peptides [4N1-1, Champs (computed helical anti-membrane proteins), LSARLAF (Leu-Ser-Ala-Arg-Leu-Ala-Phe)], proteins (histones) and large polysaccharides (fucoidan, dextran sulfate). This miscellaneous group stimulate aggregation of human and mouse platelets through the glycoprotein VI (GPVI)-FcR γ-chain complex and/or C-type lectin-like receptor-2 (CLEC-2) as shown using platelets from mice deficient in either or both of these receptors. In addition, all of these ligands stimulate tyrosine phosphorylation in GPVI/CLEC-2-double-deficient platelets, indicating that they bind to additional surface receptors, although only in the case of dextran sulfate does this lead to activation. DEP, fucoidan and dextran sulfate, but not the other agonists, activate GPVI and CLEC-2 in transfected cell lines as shown using a sensitive reporter assay confirming a direct interaction with the two receptors. We conclude that this miscellaneous group of ligands bind to multiple proteins on the cell surface including GPVI and/or CLEC-2, inducing activation. These results have pathophysiological significance in a variety of conditions that involve exposure to activating charged/hydrophobic agents.