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Question : Cette thèse comporte deux articles portant sur l’étude d’expressions faciales émotionnelles. Le processus de développement d’une nouvelle banque de stimuli émotionnels fait l’objet du premier article, alors que le deuxième article utilise cette banque pour étudier l’effet de l’anxiété de trait sur la reconnaissance des expressions statiques. Méthodes : Un total de 1088 clips émotionnels (34 acteurs X 8 émotions X 4 exemplaire) ont été alignés spatialement et temporellement de sorte que les yeux et le nez de chaque acteur occupent le même endroit dans toutes les vidéos. Les vidéos sont toutes d’une durée de 500ms et contiennent l’Apex de l’expression. La banque d’expressions statiques fut créée à partir de la dernière image des clips. Les stimuli ont été soumis à un processus de validation rigoureux. Dans la deuxième étude, les expressions statiques sont utilisées conjointement avec la méthode Bubbles dans le but d’étudier la reconnaissance des émotions chez des participants anxieux. Résultats : Dans la première étude, les meilleurs stimuli ont été sélectionnés [2 (statique & dynamique) X 8 (expressions) X 10 (acteurs)] et forment la banque d’expressions STOIC. Dans la deuxième étude, il est démontré que les individus présentant de l'anxiété de trait utilisent préférentiellement les basses fréquences spatiales de la région buccale du visage et ont une meilleure reconnaissance des expressions de peur. Discussion : La banque d’expressions faciales STOIC comporte des caractéristiques uniques qui font qu’elle se démarque des autres. Elle peut être téléchargée gratuitement, elle contient des vidéos naturelles et tous les stimuli ont été alignés, ce qui fait d’elle un outil de choix pour la communauté scientifique et les cliniciens. Les stimuli statiques de STOIC furent utilisés pour franchir une première étape dans la recherche sur la perception des émotions chez des individus présentant de l’anxiété de trait. Nous croyons que l’utilisation des basses fréquences est à la base des meilleures performances de ces individus, et que l’utilisation de ce type d’information visuelle désambigüise les expressions de peur et de surprise. Nous pensons également que c’est la névrose (chevauchement entre l'anxiété et la dépression), et non l’anxiété même qui est associée à de meilleures performances en reconnaissance d’expressions faciales de la peur. L’utilisation d’instruments mesurant ce concept devrait être envisagée dans de futures études., Question: This thesis describes a new database of facial emotional expressions; created specifically for eye-tracking and classification image experiments. This database serves as a basis for the second study, which explores the effect of trait anxiety on the perception of static facial emotional expressions. Methods: Actors were recruited to express facial emotional expressions. Thousands of 1-second movie clips that contained the least head movement and appeared genuine were extracted from the raw videos and selected for the validation. A total of 1088 clips (34 actors X 8 expressions X 4 exemplar) were spatially aligned so that facial features across the stimuli occupied the same space. They were also temporally aligned so that all clips began on the last neutral frame and truncated on the 15th frame (500ms). The last frame (apex) of the clips was extracted to form the static database. Two groups of participants validated the dynamic (N35) and static (N35) stimuli. The static images were used in the 2nd study where participants (N27) varying in trait anxiety were asked to recognize emotional faces, partially revealed through Gaussian apertures (Bubbles). Results: Study 1 describes the process by which the STOIC database was created. It showcases the 80 dynamic (and 80 static) emotional expressions (8 emotions X 10 actors) with the lowest entropy scores. Study 2 shows that trait anxiety is associated with performance and differential use of information. Anxious individuals use low spatial frequency (LSF) information from the mouth region and are better at recognizing negative emotions, especially fear and not anger. Discussion: This thesis presents a new and freely downloadable emotion recognition database containing static and dynamic stimuli. The database possesses unique characteristics that will make it useful to the scientific community and clinicians. We used the static images in the second study to establish a baseline and gain a better understanding about the use of information contained in faces to recognized emotional expressions. The next phase of the project will be to explore the effects of anxiety and depression on the perception of dynamic expressions. We speculate that the use of LSF information in our anxious group disambiguated fear from surprise and led to better performance for that emotion. In addition, we think the overlap between anxiety and depression, which was associated with better performances, may be attributed to concept of neuroticism.

Impairment in recognizing facial emotions is a prominent feature of schizophrenia patients, but the underlying mechanism of this impairment remains unclear. This study investigated the specific aspects of visual information that are critical for schizophrenia patients to recognize emotional expression. Using the Bubbles technique, we probed the use of visual information during a facial emotion discrimination task (fear vs. happy) in 21 schizophrenia patients and 17 healthy controls. Visual information was sampled through randomly located Gaussian apertures (or "bubbles") at 5 spatial frequency scales. Online calibration of the amount of face exposed through bubbles was used to ensure 75% overall accuracy for each subject. Least-square multiple linear regression analyses between sampled information and accuracy were performed to identify critical visual information that was used to identify emotional expression. To accurately identify emotional expression, schizophrenia patients required more exposure of facial areas (i.e., more bubbles) compared with healthy controls. To identify fearful faces, schizophrenia patients relied less on bilateral eye regions at high-spatial frequency compared with healthy controls. For identification of happy faces, schizophrenia patients relied on the mouth and eye regions; healthy controls did not utilize eyes and used the mouth much less than patients did. Schizophrenia patients needed more facial information to recognize emotional expression of faces. In addition, patients differed from controls in their use of high-spatial frequency information from eye regions to identify fearful faces. This study provides direct evidence that schizophrenia patients employ an atypical strategy of using visual information to recognize emotional faces.

BACKGROUND:Eye movement strategies employed by humans to identify conspecifics are not universal. Westerners predominantly fixate the eyes during face recognition, whereas Easterners more the nose region, yet recognition accuracy is comparable. However, natural fixations do not unequivocally represent information extraction. So the question of whether humans universally use identical facial information to recognize faces remains unresolved. METHODOLOGY/PRINCIPAL FINDINGS:We monitored eye movements during face recognition of Western Caucasian (WC) and East Asian (EA) observers with a novel technique in face recognition that parametrically restricts information outside central vision. We used 'Spotlights' with Gaussian apertures of 2 degrees, 5 degrees or 8 degrees dynamically centered on observers' fixations. Strikingly, in constrained Spotlight conditions (2 degrees and 5 degrees) observers of both cultures actively fixated the same facial information: the eyes and mouth. When information from both eyes and mouth was simultaneously available when fixating the nose (8 degrees), as expected EA observers shifted their fixations towards this region. CONCLUSIONS/SIGNIFICANCE:Social experience and cultural factors shape the strategies used to extract information from faces, but these results suggest that external forces do not modulate information use. Human beings rely on identical facial information to recognize conspecifics, a universal law that might be dictated by the evolutionary constraints of nature and not nurture.

An extension of the ray-pulse matrix formalism is presented that includes self-phase-modulation, self-focusing, bandwidth limitations, and Gaussian apertures. With this more complete set of matrices it is shown how self-mode-locked lasers can be modeled and how the different pulse-shaping mechanisms interact in order to provide a stable femtosecond output.

Face inversion dramatically disrupts our ability to process faces, which is known as the face inversion effect. Previous electrophysiological studies have indicated that the N170 ERP component is delayed and sometimes larger in response to inverted compared to upright faces. However, the nature of these effects remains elusive because we do not yet understand the information coding function of the N170 in upright and inverted faces. Here, we assessed what facial information the N170 codes and when it does so for upright and inverted faces. To this aim, we used one of the simplest socially relevant tasks: face detection. In this task, 10 healthy adults (5 females, median age=23, 20-29) saw pictures of faces and noise textures revealed through ten small Gaussian apertures (bubbles). Participants performed two sessions of trials with upright faces, and two sessions with inverted faces, for a total of 4400 trials. We applied reverse-correlation methods coupled with information theory to reveal the image pixels statistically associated with behaviour and neural responses. In both upright and inverted faces, we found that presence of the left eye modulated the reaction times (RTs) of all participants. In upright faces, the eye contralateral to the left and right posterior lateral electrodes strongly modulated early face ERPs. In particular, the N170 latency and amplitude coded the presence of the contralateral eye (Rousselet et al. Journal of Vision 2014, 14(13): 7, 1-24). This association was about 35% weaker in inverted faces, and delayed by about 30 ms, compared to upright face. In conclusion, our results suggest that, in a face detection task, the N170 mostly code the presence of a single feature: the contralateral eye. Inversion leads to an inefficient coding of the same feature, which is reflected in weaker and delayed feature sensitivity. Meeting abstract presented at VSS 2015.

The evolution of relevant beam parameters of a light beam propagating through an iterated sequence of spherical lenses and Gaussian apertures immersed in an active medium is investigated. This structure is a classical model for an optical resonator. The effective size of the field distribution, the beam quality factor and the radius of wave front curvature are calculated as functions of the number of transits. Steady-state values of these parameters are also determined and the dependence of the results on the gain of the medium, the aperture width and the focal length is illustrated. A comparison with the case without active medium is also discussed.

An approach aimed at completely simulating the operation of camera or telescope, including direct calculation of images, in a spatially complex, turbid environment is presented. A Monte Carlo radiative transfer program coupled with an optics design program is used to compute aureoles at the image plane of a camera. The procedure uses the camera MTF so that the operation of the camera in a scattering environment can be completely simulated. The code is validated through a comparison of the analytical solutions for cameras with plane and Gaussian apertures.

Humans recognize basic facial expressions effortlessly. Yet, despite a considerable amount of research, this task remains elusive for computer vision systems. Here, we compared the behavior of one of the best computer models of facial expression recognition (Z. Hammal, L. Couvreur, A. Caplier, & M. Rombaut, 2007) with the behavior of human observers during the M. Smith, G. Cottrell, F. Gosselin, and P. G. Schyns (2005) facial expression recognition task performed on stimuli randomly sampled using Gaussian apertures. The model--which we had to significantly modify in order to give the ability to deal with partially occluded stimuli--classifies the six basic facial expressions (Happiness, Fear, Sadness, Surprise, Anger, and Disgust) plus Neutral from static images based on the permanent facial feature deformations and the Transferable Belief Model (TBM). Three simulations demonstrated the suitability of the TBM-based model to deal with partially occluded facial parts and revealed the differences between the facial information used by humans and by the model. This opens promising perspectives for the future development of the model.

A novel 3 × 3 transfer-matrix method is developed to propagate off-axis Gaussian beams in astigmatic optical systems that may include tilted, displaced, or curved optical elements. Unlike in a previous generalized ray matrix formalism, optical elements that possess gain or loss such as Gaussian apertures, complex lenslike media, and amplifiers are included; and a new beam transformation is found. In addition, a novel exponential variable-reflectivity mirror, which displaces a Gaussian beam without changing its spot size, and a complex prismlike medium are introduced.

It is demonstrated that the definition of a fractional-order Fourier transform can be extended into the complexorder regime. A complex-order Fourier transform deals with the imaginary part as well as the real part of the exponential function in the integral. As a result, while the optical implementation of fractional-order Fourier transform involves gradient-index media or spherical lenses, the optical interpretation of complex-order Fourier transform is practically based on the convolution operation and Gaussian apertures. The beam width of a Gaussian beam subjected to the complex-order Fourier transform is obtained analytically with the ABCD matrix approach.

The evolution of the main parameters (spot size, radius of curvature, and far-field divergence) of the beam provided by a high-gain, short-pulse Xe–Cl laser equipped with a plane-parallel Gaussian resonator has been investigated both theoretically and experimentally as a function of the number of round trips. It is shown that a theoretical analysis, formerly developed to study the growth of coherence of a Schell–Gauss model beam propagating through a periodic sequence of Gaussian apertures, provides a satisfactory description of the temporal evolution of the Xe–Cl laser beam. A good agreement between theoretical and experimental data has been found.

In this communication we have studied the imaging properties of the recently fabricated Selfoc lens. The theoretical results have been compared with the available experimental data. A brief discussion of diffraction by gaussian apertures has also been included.

In humans, the N170 event-related potential (ERP) is an integrated measure of cortical activity that varies in amplitude and latency across trials. Researchers often conjecture that N170 variations reflect cortical mechanisms of stimulus coding for recognition. Here, to settle the conjecture and understand cortical information processing mechanisms, we unraveled the coding function of N170 latency and amplitude variations in possibly the simplest socially important natural visual task: face detection. On each experimental trial, 16 observers saw face and noise pictures sparsely sampled with small Gaussian apertures. Reverse-correlation methods coupled with information theory revealed that the presence of the eye specifically covaries with behavioral and neural measurements: the left eye strongly modulates reaction times and lateral electrodes represent mainly the presence of the contralateral eye during the rising part of the N170, with maximum sensitivity before the N170 peak. Furthermore, single-trial N170 latencies code more about the presence of the contralateral eye than N170 amplitudes and early latencies are associated with faster reaction times. The absence of these effects in control images that did not contain a face refutes alternative accounts based on retinal biases or allocation of attention to the eye location on the face. We conclude that the rising part of the N170, roughly 120-170 ms post-stimulus, is a critical time-window in human face processing mechanisms, reflecting predominantly, in a face detection task, the encoding of a single feature: the contralateral eye.

Bu makalede, Gauss hüzme dizisinin üretimi için alternatif deneysel bir yöntem önerilmiştir. Bu amaç doğrultusunda, ışık hüzmeleri düzlem dalganın Gaussian açıklık dizisinden kırılımına göre modellenmiş ve buna göre elde edilmiştir. Gauss hüzme dizisinin uzaysal üretimi Uzaysal Işık Modülatörü SLM kullanılarak deneysel olarak gerçekleştirilmiştir. Üretilen ışık hüzmeleri geniş görüş açılı bir CCD dedektörü tarafından kayıt edilmiş ve gözlemlenen hüzmelerin profil değerlendirmesi yapılmıştır. Buna ek olarak teorik hesaplamalar deneysel gözlemlerle doğrulanmıştır. Önerilen bu yeni hüzme şekil üretme yöntemi ile Gauss hüzme dizisinin üretilmesi ve gerçek zamanlı kontrolü, optik haberleşme ve biyofotonik gibi yüksek kazançlı fotonik uygulamaları için mümkün hale gelebilir, In this paper, an alternative experimental method is proposed in relevant to generation of Gauss beam array. For this purpose, light beams are modelled based on the diffraction of plane wave by an array of Gaussian apertures and implemented accordingly. Spatial generation Gauss beam array has been performed experimentally by the use of Spatial Light Modulator SLM . Produced light beams are recorded by a large field of view Charge Couple Device CCD detector and profile evaluations of monitored beams are done. Moreover, theoretical calculations have been verified with the empirical observations. With this proposed new beam shaping method, it is possible to generate and control the Gauss beam array in real time for many high throughput photonic applications such as optical communications and biophotonics.

A modified matrix model is proposed for stable cavities with intracavity Gaussian apertures, which approximate real apertures. This model differs from the known ones by a better grounded approach to selection of the Gaussian aperture parameters. Analytic relationships are derived for calculating the energy divergence angle of the output radiation and of the beam diameter at the output mirror position under multimode emission conditions. It is shown that the spatial characteristics of the beam are determined by the aperture diameter and by the complex magnification, which is an analogue of the geometric magnification used in the description of unstable cavities. The calculated results are in good agreement with experimental data.