Search

The emergence of visual cortex specialization for culturally acquired characters like letters and digits, both arbitrary shapes related to specific cognitive domains, is yet unclear. Here, 20 young children (6.12 years old) were tested with a frequency-tagging paradigm coupled with electroencephalogram recordings to assess discrimination responses of letters from digits and vice-versa. One category of stimuli (e.g., letters) was periodically inserted (1/5) in streams of the other category (e.g., digits) presented at a fast rate (6 Hz). Results show clear right-lateralized discrimination responses at 6 Hz/5 for digits within letters, and a trend for left-lateralization for letters. These results support an early developmental emergence of ventral occipito-temporal cortex specialization for visual recognition of digits and letters, potentially in relation with relevant coactivated brain networks. [ABSTRACT FROM AUTHOR]

The developmental course of neural tuning to visual letter strings is unclear. Here we tested 39 children longitudinally, at the beginning of grade 1 (6.45 ± 0.33 years old) and 1 year after, with fast periodic visual stimulation in electroencephalography to assess the evolution of selective neural responses to letter strings and their relationship with emerging reading abilities. At both grades, frequency‐tagged letter strings were discriminated from pseudofont strings (i.e. letter‐selectivity) over the left occipito‐temporal cortex, with effects observed at the individual level in 62% of children. However, visual words were not discriminated from pseudowords (lexical access) at either grade. Following 1 year of schooling, letter‐selective responses showed a specific increase in amplitude, a more complex pattern of harmonics, and were located more anteriorly over the left occipito‐temporal cortex. Remarkably, at both grades, neural responses were highly significant at the individual level and correlated with individual reading scores. The amplitude increase in letter‐selective responses between grades was not found for discrimination responses of familiar keyboard symbols from pseudosymbols, and was not related to a general increase in visual stimulation responses. These findings demonstrate a rapid onset of left hemispheric letter selectivity, with 1 year of reading instruction resulting in increased emerging reading abilities and a clear quantitative and qualitative evolution within left hemispheric neural circuits for reading., A group of 39 young children were tested with FPVS‐EEG to understand changes in the left hemisphere when learning to read. After only 1 year of schooling, a quantitative and qualitative evolution in the selective neural responses to letters is found, independently of a general increase of visual stimulation responses.

The developmental course of neural tuning to visual letter strings is unclear. Here we tested 39 children longitudinally, at the beginning of grade 1 (6.45 ± 0.33 years old) and 1 year after, with fast periodic visual stimulation in electroencephalography to assess the evolution of selective neural responses to letter strings and their relationship with emerging reading abilities. At both grades, frequency-tagged letter strings were discriminated from pseudofont strings (i.e. letter-selectivity) over the left occipito-temporal cortex, with effects observed at the individual level in 62% of children. However, visual words were not discriminated from pseudowords (lexical access) at either grade. Following 1 year of schooling, letter-selective responses showed a specific increase in amplitude, a more complex pattern of harmonics, and were located more anteriorly over the left occipito-temporal cortex. Remarkably, at both grades, neural responses were highly significant at the individual level and correlated with individual reading scores. The amplitude increase in letter-selective responses between grades was not found for discrimination responses of familiar keyboard symbols from pseudosymbols, and was not related to a general increase in visual stimulation responses. These findings demonstrate a rapid onset of left hemispheric letter selectivity, with 1 year of reading instruction resulting in increased emerging reading abilities and a clear quantitative and qualitative evolution within left hemispheric neural circuits for reading.

This thesis examines whether and how odors contribute to the development of visual categorization in the human brain using fast periodic visual stimulation coupled with scalp electroencephalography (FPVS-EEG). Specifically, we sought to characterize if a neural visual response selective to the face category is modulated by the presence of a body odor in both infants (Study 1, 2, 3) and adults (Study 4).In infants, the selectivity of the odor effect on visual categorization was addressed by testing separately three categories in three groups of 4-month-old infants presented with a control odor or their mother’s odor. We observed that a face-selective response is largely enhanced by maternal odor over the right occipito-temporal cortex (Study 1). By contrast, a car-selective response, observed over the right occipital region, is insensitive to the presence of maternal odor (Study 2). Finally, when using nonface objects configured as faces (i.e., facelike objects), a facelike-selective response is amplified over the right hemisphere when infants are exposed to maternal odor, and even initiated in some infants who do not selectivly respond to facelike objects in the absence of maternal odor (Study 3). In adults, the selective responses to human faces, cars and facelike objects were recorded in a body, gasoline, or control odor context (Study 4). While the categorization of human faces or cars is immune to the presence of odors, the body odor enhances the facelike-selective response, suggesting a facilitating effect of a congruent odor when the visual categroy is ambiguous. For these four studies, the general visual response elicited by all stimuli in the rapid visual sequence remains stable across odor contexts, excluding any general effect of odors in terms of arousal/attention.Altogether, these findings demonstrate a strong facilitative effect of body odors on congruent visual categorizations (i.e., human or illusory faces). We thus illustrate through olfactory-visual associations that information from different senses are integrated to facilitate visual categorization, especially early in life when the visual system is still immature, and that these intersensory congruent associations are maintained until adulthood in the case of ambiguous visual stimuli., Cette thèse examine dans quelle mesure les odeurs contribuent au développement de la catégorisation visuelle dans le cerveau humain à l’aide d’une stimulation visuelle périodique rapide couplée à l’électroencéphalographie de surface (FPVS-EEG). Nous avons en particulier cherché à caractériser si une réponse cérébrale sélective à la catégorie visuelle des visages est modulées par la présence d’une odeur corporelle chez le nourrisson (Etudes 1 à 3) et l'adulte (Etude 4).Chez le nourrisson, la sélectivité de l'effet de l’odeur sur la categorisation visuelle a été testée à l’aide de trois catégories étudiées séparément chez trois groupes de nourrissons de 4 mois exposés à une odeur contrôle ou à l’odeur de leur mère. Nous avons observé qu’une réponse sélective aux visages est largement amplifiée par l'odeur maternelle en regard du cortex occipito-temporal droit (Etude 1). En revanche, une réponse sélective aux voitures, mesurée au niveau de la région occipitale droite, ne présente aucun effet de l'odeur (Etude 2). Enfin, en utilisant des objets non faciaux configurés comme des visages (visages illusoires), une réponse sélective à ces visages illusoires est amplifiée au niveau de l’hémisphère droit en présence de l'odeur maternelle, et même intiée chez certains nourrissons qui ne répondent pas à ces visages illusoire en l’absence de l’odeur maternelle (Etude 3). Chez l’adulte, les réponses sélectives aux visages humains, voitures et visages illusoires ont été mesurées en présence d’odeurs corporelles, de gasoil ou d’une odeur contrôle (Etude 4). Tandis que la categorisation des visages humains ou des voitures n’est pas affectée par la présence des odeurs, l’odeur corporelle amplifie la réponse sélective aux visages illusoires, suggérant un effet facilitateur d’une odeur congruente quand la catégorie visuelle est ambigüe. Dans ces quatre études, la réponse visuelle générale élicitée par l’ensemble des stimuli de la séquence visuelle rapide reste stable entre les contextes olfactifs testés, excluant un effet général des odeurs en termes d’éveil/d’attention.Dans l’ensemble, ces résultats démontrent un effet facilitateur important des odeurs corporelles sur la catégorisation d’informations visuelles congruentes (visages humains ou illusoires). Nous illustrons ainsi par ces associations olfacto-visuelles que les informations provenant de différents sens sont intégrées pour favoriser la catégorisation visuelle, particulièrement en début de vie lorsque le système visuel est encore immature, et que ces associations intersensorielles congruentes se maintiennent jusqu’à l’âge adulte dans le cas de stimuli visuels ambigus.

The developmental origin of human adults’ right hemispheric dominance in response to face stimuli remains unclear, in particular because young infants’ right hemispheric advantage in face‐selective response is no longer present in preschool children, before written language acquisition. Here we used fast periodic visual stimulation (FPVS) with scalp electroencephalography (EEG) to test 52 preschool children (5.5 years old) at two different levels of face discrimination: discrimination of faces against objects, measuring face‐selectivity, or discrimination between individual faces. While the contrast between faces and nonface objects elicits strictly bilateral occipital responses in children, strengthening previous observations, discrimination of individual faces in the same children reveals a strong right hemispheric lateralization over the occipitotemporal cortex. Picture‐plane inversion of the face stimuli significantly decreases the individual discrimination response, although to a much smaller extent than in older children and adults tested with the same paradigm. However, there is only a nonsignificant trend for a decrease in right hemispheric lateralization with inversion. There is no relationship between the right hemispheric lateralization in individual face discrimination and preschool levels of readings abilities. The observed difference in the right hemispheric lateralization obtained in the same population of children with two different paradigms measuring neural responses to faces indicates that the level of visual discrimination is a key factor to consider when making inferences about the development of hemispheric lateralization of face perception in the human brain., Using a fast periodic visual presentation paradigm combined with EEG we show that the right hemisphere involvement in face processing depends on discrimination level in preschool children. While face individuation (identity) relies on the right hemisphere, bilateral occipital networks were activated by generic face categorization (faces vs objects). Since right lateralization is present in pre‐readers these results challenge the hypothesis that learning to reading entails the right‐lateralization for faces observed in adulthood.

The developmental origin of human adults’ right hemispheric dominance in response to face stimuli remains unclear, in particular because young infants’ right hemispheric advantage in face-selective response is no longer present in preschool children, before written language acquisition. Here we used fast periodic visual stimulation (FPVS) with scalp electroencephalography (EEG) to test 52 preschool children (5.5 years old) at two different levels of face discrimination: discrimination of faces against objects, measuring face-selectivity, or discrimination between individual faces. While the contrast between faces and nonface objects elicits strictly bilateral occipital responses in children, strengthening previous observations, discrimination of individual faces in the same children reveals a strong right hemispheric lateralization over the occipitotemporal cortex. Picture-plane inversion of the face stimuli significantly decreases the individual discrimination response, although to a much smaller extent than in older children and adults tested with the same paradigm. However, there is only a nonsignificant trend for a decrease in right hemispheric lateralization with inversion. There is no relationship between the right hemispheric lateralization in individual face discrimination and preschool levels of readings abilities. The observed difference in the right hemispheric lateralization obtained in the same population of children with two different paradigms measuring neural responses to faces indicates that the level of visual discrimination is a key factor to consider when making inferences about the development of hemispheric lateralization of face perception in the human brain.

Présentation Poster; International audience; In the 4-month-old infant brain, the visual categorization of natural face images is enhanced by concomitant maternal odor (Leleu et al., 2019), providing support for the early perception of congruent associations between co-occurring inputs from multiple senses. Here, we further explore whether this maternal odor effect is selective to faces or if it can be explained by a more general influence of salient odor cues on the perception of any visual object category. In Experiment 1, scalp electroencephalogram was recorded during a fast periodic visual stimulation (FPVS-EEG) while 4-month-old infants were exposed to the maternal vs. a control odor. In rapid 6-Hz streams of natural images (i.e., 6 stimuli per second), images of cars instead of faces were interspersed every 6th stimulus among other nonface objects (i.e., at 1 Hz). We isolated a neural categorization response to cars at the predefined 1-Hz frequency over the right occipital region in both odor contexts, showing the ability of infants to categorize variable exemplars of cars at a glance. However, maternal odor did not enhance this response, supporting its face-selective influence. In Experiment 2, images of nonface objects resembling faces (i.e., facelike stimuli) were used as the target category, i.e., interleaved every 6th image in the stream of stimulation. The brain response to facelike objects was faint yet clearly identifiable over bilateral occipito-temporal sites in the control odor condition, revealing infants' sensitivity to facelike patterns in a fast train of various categories of living and nonliving objects. More importantly, we observed that maternal odor magnified the facelike categorization response over the right hemisphere in a majority of infants, showing that this highly relevant odor triggers a face-selective neural activity even in the absence of genuine human faces. In both experiments, the general visual response elicited by the rapid 6-Hz stimulation was immune to the maternal odor effect, excluding any account in terms of an undifferentiated increase of visual attention or arousal in the maternal odor context. Altogether, these experiments provide evidence for the tuning of face(like) categorization from multisensory inputs in the developing brain. They accord with the view that perceptual development integrates information across the senses for efficient category acquisition, with early-maturing systems, such as olfaction, providing assistance to later-developing systems, such as vision.

International audience; Humans exhibit a marked specialization to process the most experienced facial morphologies. In particular, nonhuman primate faces are poorly discriminated compared to human faces in behavioral tasks. So far however, a clear and consistent marker that quantifies our expertise in human over monkey face discrimination directly from brain activity is lacking. Here, using scalp electroencephalography (EEG), we isolate a direct signature of individuation abilities for human and nonhuman (i.e., macaque faces) primate faces. Human or monkey faces were rapidly presented at a base rate of 12Hz in upright or inverted orientations while participants performed an orthogonal behavioral task. In each stimulation sequence, eight face images of one individual were used as base stimuli, while images of other individuals were briefly introduced every 9th stimulus to quantify an identity-change response at 1.33Hz and harmonics (i.e., integer multiples) in the EEG frequency spectrum. The brain response to upright human faces was twice as large as to monkey faces, and reduced following picture-plane inversion for human faces only. This reflects the disruption of high-level face identity discrimination developed for the canonical upright human face. No difference was observed between upright monkey faces and inverted human faces, suggesting non-expert visual processes for those two face formats associated with little experience. In addition, the size of the inversion effect for human, but not monkey faces, was predictive of the expertise effect (i.e., difference between upright human and monkey faces) at the individual level. This result suggests a selective ability to discriminate human faces that does not contribute to the individuation of other unexperienced face morphologies such as monkey faces. Overall, these findings indicate that human expertise for conspecific face discrimination can be isolated and quantified in individual human brains.

This thesis examines the mechanisms subtending the perception of emotional facial expressions and their early development using a Fast Periodic Visual Presentation (FPVS) approach coupled with electroencephalography (EEG). More specifically, we tried to characterize brain responses reflecting facial expression discrimination and to determine whether hedonic odor contexts influence these responses in adults (studies 1 and 2), and in infants at different developmental stages (studies 3 and 4).We showed specific responses to the discrimination of every facial expression in the adult brain, indicating rapid and automatic categorization of basic facial expressions (study 1). In addition, we revealed that hedonic odor contexts influence these expression-specific brain responses. While the response to happiness is unchanged, the response to disgust is weaker in both pleasant and unpleasant odor contexts. The odor effect is strong for the response to neutrality, this response being nearly absent in the unpleasant odor context vs. larger in the pleasant context. Hedonic odors could thus orient facial expression perception toward their own emotional valence, or toward the valence of the odor for the emotionally ambiguous neutral expression, hampering or facilitating their discrimination from the other mainly negative expressions (study 2). In infants, a first study isolated brain responses to the discrimination of facial expressions in 3.5- and 7-month-olds (study 3). In particular, we observed that the response to happiness evolves between 3.5- and 7-month-old (additional fronto-central activity), suggesting the progressive integration of the emotional meaning of this positive expression. The second study has been initiated in 7-month-old infants to test the influence of a pleasant hedonic odor context on the specific brain response to happiness (study 4, ongoing study). This study seems to indicate that the response is larger in a pleasant rather than neutral odor context.These results reveal that facial expressions are readily discriminated in adults, hedonic odor contexts orienting perception toward emotional valence rather than related basic emotions. Emotional valence may be acquired early in development, before 7 months, since the discrimination of happiness (positive) from other expressions (mainly negative) evolves at this age. Moreover, at 7 months, the perception of happiness seems facilitated by the presence of a pleasant odor context. Hence, due to the early functional maturity of the olfactory system, odors may actively participate in acquiring the emotional meaning of facial expressions during early development and facilitate the perception of expressions whose emotional meaning is ambiguous in adults. Overall, our work sheds new light on the role of multisensory integration during early perceptual development and opens interesting perspectives to investigate typical and atypical socio-cognitive and affective development., Cette thèse se propose d’examiner les mécanismes de la perception des expressions faciales émotionnelles et leur développement précoce, grâce à une approche de présentation visuelle périodique rapide (Fast Periodic Visual Presentation : FPVS) couplée à l’électroencéphalographie (EEG). Plus spécifiquement, nous avons cherché à caractériser des réponses cérébrales de discrimination des expressions faciales et à déterminer l’influence d’un contexte olfactif hédonique sur ces réponses, chez l’adulte (Etudes 1 et 2) ainsi que chez le nourrisson à différents stades de développement (Etudes 3 et 4).Nous avons montré que l’adulte présente des réponses cérébrales distinctes selon l’expression faciale cible à discriminer, indiquant une catégorisation spontanée des expressions faciales de base (Étude 1). Par ailleurs, nous avons mis en évidence que la présence d’un contexte olfactif hédonique influence les réponses cérébrales de catégorisation des expressions faciales. Tandis que la réponse à la joie reste inchangée, la réponse au dégoût est moindre en présence d’un contexte olfactif hédonique agréable ou désagréable. L’effet de l’odeur est particulièrement retrouvé pour la réponse à la neutralité, la réponse étant presque absente en contexte désagréable vs. amplifiée en contexte agréable. Les odeurs hédoniques orienteraient ainsi la perception des expressions faciales vers leur propre valence émotionnelle, ou vers la valence de l’odeur pour l’expression neutre émotionnellement ambiguë, entravant ou facilitant leur discrimination des autres expressions, majoritairement négatives (Etude 2). Chez le nourrisson, une première étude a permis d’isoler des réponses cérébrales de discrimination des expressions faciales à 3,5 et 7 mois (Étude 3). Une évolution de la réponse cérébrale à la joie a été observée entre 3,5 et 7 mois (activité fronto-centrale additionnelle), suggérant l’intégration progressive de la signification émotionnelle de cette expression positive. La seconde étude a été initiée chez les nourrissons de 7 mois pour tester l’influence d’un contexte olfactif agréable sur la réponse cérébrale à l’expression de joie (Etude 4, en cours). Elle semble indiquer que la réponse à la joie est amplifiée par un contexte olfactif agréable plutôt que neutre.Ces résultats révèlent que les expressions faciales sont facilement discriminées chez l’adulte, la présence d’un contexte olfactif hédonique orientant la perception vers la valence émotionnelle de l’expression faciale plutôt que vers l’émotion de base associée en tant que telle. La valence émotionnelle des expressions pourrait être acquise précocement au cours du développement, avant 7 mois, âge auquel évolue la discrimination de la joie (positive) par rapport aux autres expressions (majoritairement négatives). En outre, à cet âge, la perception de la joie semble facilitée en présence d’un contexte olfactif agréable. Ainsi, du fait de la maturité fonctionnelle précoce du système olfactif, les odeurs pourraient activement participer à l’acquisition de la signification émotionnelle des expressions faciales au cours du développement, et faciliter la perception des expressions dont la signification émotionnelle est ambiguë chez l’adulte. Dans l’ensemble, nos travaux éclairent le rôle de l’intégration multisensorielle au cours du développement perceptif précoce et ouvrent d’intéressantes perspectives pour investiguer le développement sociocognitif et affectif typique et atypique.