Optical and electrical recording of neural activity evoked by graded contrast visual stimulus

BackgroundBrain activity has been investigated by several methods with different principles, notably optical ones. Each method may offer information on distinct physiological or pathological aspects of brain function. The ideal instrument to measure brain activity should include complementary techniques and integrate the resultant information. As a "low cost" approach towards this objective, we combined the well-grounded electroencephalography technique with the newer near infrared spectroscopy methods to investigate human visual function.MethodsThe article describes an embedded instrumentation combining a continuous-wave near-infrared spectroscopy system and an electroencephalography system to simultaneously monitor functional hemodynamics and electrical activity. Near infrared spectroscopy (NIRS) signal depends on the light absorption spectra of haemoglobin and measures the blood volume and blood oxygenation regulation supporting the neural activity. The NIRS and visual evoked potential (VEP) are concurrently acquired during steady state visual stimulation, at 8 Hz, with a b/w "windmill" pattern, in nine human subjects. The pattern contrast is varied (1%, 10%, 100%) according to a stimulation protocol.ResultsIn this study, we present the measuring system; the results consist in concurrent recordings of hemodynamic changes and evoked potential responses emerging from different contrast levels of a patterned stimulus.The concentration of [HbO2] increases and [HHb] decreases after the onset of the stimulus. Their variation shows a clear relationship with the contrast value: large contrast produce huge difference in concentration, while low contrast provokes small concentration difference. This behaviour is similar to the already known relationship between VEP response amplitude and contrast.ConclusionThe simultaneous recording and analysis of NIRS and VEP signals in humans during visual stimulation with a b/w pattern at variable contrast, demonstrates a strong linear correlation between hemodynamic changes and evoked potential amplitude. Furthermore both responses present a logarithmic profile with stimulus contrast

Reproduire un cercle et en parler en classe de mathématique : est-ce si simple ? Quelques éléments d’analyse d’une étude didactique comparant trois mises en œuvre d’une même situation

Intéressées par des questions sur les rôles des interactions langagières dans l’enseignement et d’apprentissage de la géométrie à l’école primaire, nous analysons ici les données recueillies dans trois classes différentes où un même problème a été proposé (reproduire un cercle). Les analyses proposées ici mettent au jour des éléments potentiellement différenciateurs en termes d’apprentissage venant d’une gestion de connaissances implicites très différentes chez les trois enseignantes observées.Interested in the question of the roles of language interactions in the teaching and learning of geometry in primary school, we analyze here the data collected in three different classes where the same problem has been proposed (reproduce a circle). The analyses proposed here reveal potentially differentiating elements in terms of learning coming from a very different implicit knowledge, in the three teachers observed

Operational Momentum During Ordering Operations for Size and Number in 4-Month-Old Infants

An Operational Momentum (OM) effect is shown by 9-month-old infants during non-symbolic arithmetic, whereby they overestimate the outcomes to addition problems, and underestimate the outcomes to subtraction problems. Recent evidence has shown that this effect extends to ordering operations for size-based sequences in 12-month-olds. Here we provide evidence that OM occurs for ordering operations involving numerical sequences containing multiple quantity cues, but not size-based sequences, already at 4 months of age. Infants were tested in an ordinal task in which they detected and represented increasing or decreasing variations in physical and/or numerical size, and then responded to ordinal sequences that exhibited greater or lesser sizes/numerosities, thus following or violating the OM generated during habituation. Results showed that OM was absent during size ordering (Experiment 1), but was present when infants ordered arrays of discrete elements varying on numerical and non-numerical dimensions, if both number and continuous magnitudes were available cues to discriminate between with-OM and against-OM sequences during test trials (Experiments 2 vs. 3). The presence of momentum for ordering number only when provided with multiple cues of magnitude changes suggests that OM is a complex phenomenon that blends multiple representations of magnitude early in infancy

Cues for Early Social Skills: Direct Gaze Modulates Newborns' Recognition of Talking Faces

Previous studies showed that, from birth, speech and eye gaze are two important cues in guiding early face processing and social cognition. These studies tested the role of each cue independently; however, infants normally perceive speech and eye gaze together. Using a familiarization-test procedure, we first familiarized newborn infants (n = 24) with videos of unfamiliar talking faces with either direct gaze or averted gaze. Newborns were then tested with photographs of the previously seen face and of a new one. The newborns looked longer at the face that previously talked to them, but only in the direct gaze condition. These results highlight the importance of both speech and eye gaze as socio-communicative cues by which infants identify others. They suggest that gaze and infant-directed speech, experienced together, are powerful cues for the development of early social skills

Object perception in early infancy: the role of attentional and perceptual processes

One central issue in developmental cognitive science is to understand how infants detect the meaningful units in the flow of perceptual information and integrate these units into a coherent structure. Actually, at any given moment the infant is confronted with a visual field that must be differentiated into objects and from which one of these objects must be selected as the next focus of attention. Perceptual binding and selective spatial attention are two fundamental processes that help to perceive the outside world. Binding is necessary to link the different features of a single object. Selective attention serves to focus onto small subset of incoming information. The selection and binding of the various parts of an object in the correct combination pose little difficulty for adults, who readily report veridical object perception under most viewing conditions (Kellman & Shipley, 1991). It is still not clear however how exactly these two mechanisms operate and interact in early infancy. Using real and illusory figures and habituation and visual search tasks, the purpose of this thesis was to study the role of perceptual and attentional processes affect object processing from birth to early infancy. In Study 1, using the habituation technique, a first set of experiments has investigated whether newborns were able to link together spatially separated fragments to perceive the unity of a moving rod partly occluded by a moving Kanizsa-type illusory box (Experiment 1, 2 and 3). Recent evidence demonstrated that 1- to 3-day old babies can fill in spatial gaps when they are asked to perceive the unity of a partly occluded object (i.e. amodal completion, Valenza, Leo, Gava, & Simion, 2006), or when they are asked to perceive an illusory object composed from a number of spatially separate elements (i.e. modal completion, Valenza & Bulf, 2007). In the present study, both modal (illusory box) and amodal (occluded rod) visual completions had to be simultaneously used to solve the perceptual task. Results showed that newborns perceived the partly occluded rod and the illusory box as complete objects, providing evidence that, at least when motion information was used, newborn infants were able to utilize simultaneously modal and amodal completions to perceive object unity. These findings support also the hypothesis that dynamic displays facilitate the solution of many perceptual tasks because motion triggers infant’s attention toward the visual information that must be integrated. In other words, the results of the first three experiments reported in my thesis suggest that, beside perceptual binding, even attention has a crucial role in perceiving veridical object during early infancy. Using an eye tracker system, in a subsequent experiment (Experiment 4) saccades latency, which is a standard variable to measure orienting of attention in infancy (Cohen, 1972), was measured to determine whether a Kanizsa illusory figure triggers 6-month-old infants attention over a control stimulus. Results showed that infants detected the illusory figure faster than the illusory one, showing that the Kanizsa figure was able to orient infants’ visual spatial attention. Overall, this outcome demonstrates that both perceptual binding (Experiments 1,2 and 3) and selective spatial attention (Experiment 4) support the perception of an illusory figure in early infancy. In Study 2, it was investigated the relation between perceptual binding and selective spatial attention, to determine how selective attention drives the binding of the single features of an object. Using an eye tracker system, adults’ and 6-month-old infants’ visual search behaviour was compared in a visual search task of an illusory figure. Visual search of illusory figures is usually used in adults’ literature to assess whether the binding of different fragments of an illusory object is independent of selective spatial attention or, on the contrary, whether perceptual binding requires spatial attention to be performed (e.g., Driver & Davis, 1994). The eye tracker system allowed us to use the same stimuli and procedure for adults and infants and, as a consequence, to directly compare adults’ and infants’ visual behavior. Participants were presented with an illusory figure and a real figure embedded in a display of competing stimuli (Experiments 5-9). The illusory figure was clearly seen due to the visual binding of its inducing elements, although a large part of their contour was not present. The analysis of the visual scanning patterns showed that both the illusory figures and the real figures automatically trigger visual spatial attention in adults (i.e. pop out effect), providing evidence that adults’ perceptual binding of separate elements to perceive an illusory object does not require spatial attention. In contrast to adult’s data, infants show a pop out effect only when a high salient real target has to be detected (Experiment 7). Conversely, when an illusory target (Experiments 7 and 9) was used, or when the real target-distractors similarity was increased (Experiment 9), infants spread out their attention within the display in a casual manner, showing that in early infancy the binding processes involved in the perception of an illusory figure do not operate in an adult-like manner. Overall these data demonstrate that, although perceptual (Experiments 1-3) and attentional (Experiment 4) processes in supporting the binding of an illusory figure are functional very early during the development, infants are not able to automatically bind an illusory figure when it is presented in among competing stimuli, as found in adults (Experiment 5-9). This outcome suggests that selective attention is determinant to affect the way in which perceptual binding operates during early infancy, leading to the ability to perform binding automatically, as found in the adults’ visual system.Uno dei problemi fondamentali nello studio dello sviluppo cognitivo è quello di comprendere in che modo i bambini riescono a segmentare il flusso continuo di informazioni che ricevono dall’ambiente in unità percettive discrete e ad integrare tali unità in strutture percettive coerenti. Infatti, l’ambiente che ci circonda è generalmente costituito da un insieme complesso e strutturato di oggetti presenti simultaneamente nel campo visivo. Di conseguenza, fin dalle prime settimane di vita il nostro sistema visivo deve selezionare e integrare l’informazione proveniente dall’ambiente per percepire gli oggetti come separati e distinti. Il processo percettivo che permette di integrare le singole caratteristiche di un oggetto è indicato in letteratura con il termine figural binding. Il binding percettivo e l’attenzione selettiva sono due processi fondamentali per percepire gli oggetti come unità discrete. Il binding percettivo permette al sistema visivo di integrare le singole parti di un oggetto. L’attenzione selettiva permette di selezionare le informazioni rilevanti per la percezione di oggetti unitari e di focalizzarsi sui singoli oggetti all’interno della scena visiva. Negli adulti, tali processi operano in modo estremamente rapido ed efficace (Kellman & Shipley, 1991). Tuttavia, non è chiaro come il binding percettivo e l’attenzione selettiva interagiscono nel supportare l’integrazione delle diverse caratteristiche di un oggetto nei primi mesi di vita. Lo scopo della mia tesi era quello di indagare il ruolo dei processi attentivi e percettivi nella percezione di oggetti alla nascita e nei primi mesi di vita, in situazioni sperimentali in cui sono state presentate sia figure reali che figure illusorie e in cui i bambini sono stati testati attraverso compiti di abituazione visiva e di ricerca visiva. Nel primo studio, utilizzando la tecnica dell’abituazione, sono stati condotti tre esperimenti per indagare la capacità di bambini neonati di percepire una barra verticale parzialmente occlusa da una barra orizzontale costituita da contorni illusori quali quelli di Kanizsa. Sia la barra verticale che la barra orizzontale sono state presentate in movimento (Esperimenti 1, 2 e 3). Recentemente è stato dimostrato che, fin dalla nascita, i bambini sono in grado di percepire un oggetto parzialmente occluso (i.e., completamento amodale, Valenza, Leo, Gava, e Simion, 2006), e di percepire una figura illusoria di Kanizsa (i.e., completamento modale, Valenza e Bulf, 2007). In questo studio la percezione dell’oggetto occluso era possibile solamente grazie al contemporaneo completamento amodale della barra verticale e al completamento modale dell’occusore illusorio. I risultati hanno dimostrato che, i neonati hanno percepito la barra occlusa e l’occlusore illusorio come oggetti unitari, dimostrando così che fin dalla nascita, almeno quando gli stimoli sono presentati in movimento, il nostro sistema visivo è in grado di utilizzare contemporaneamente i processi di completamento modale e amodale per integrare l’informazione visiva e, di conseguenza, percepire gli oggetti come unitari. Inoltre, questi risultati supportano l’ipotesi che l’informazione cinetica facilita la percezione di oggetti alla nascita, attirando l’attenzione del bambino verso gli elementi visivi che devono essere integrati per la soluzione del compito percettivo. In altre parole, i risultati dei primi tre esperimenti del presente lavoro di tesi suggeriscono che, oltre a processi di completamento percettivo, nella prima infanzia l’attenzione selettiva è un processo fondamentale per veicolare la percezione di oggetti unitari. Utilizzando un sistema per la registrazione dei movimenti oculari (i.e., eye tracker), è stato verificato se una figura di Kanizsa catturava l’attenzione di bambini di 6 mesi di vita in un compito di preferenza visiva in cui la figura illusoria era presentata assieme ad una figura di controllo. L’eye tracker ha permesso di registrare la latenza della prima saccade verso i due stimoli, una variabile standard per misurare l’orientamento attentivo nei primi mesi di vita (Cohen, 1972). I risultati hanno dimostrato che i bambini hanno selezionato più velocemente la figura di Kanizsa rispetto allo stimolo di controllo, dimostrando che l’attenzione è stata catturata dalla figura di Kanizsa. Complessivamente, i risultati di questo primo studio hanno dimostrato che, nei primi mesi di vita, sia i processi di binding percettivo (Esperimenti 1, 2 e 3), che i processi di attenzione selettiva (Esperimento 4) supportano la percezione di un oggetto illusorio. Nel secondo studio è stata indagata la relazione tra i processi di binding percettivo e i processi di attenzione selettiva nell’integrare le singole caratteristiche di un oggetto. Utilizzando l’eye tracker, adulti e bambini di 6 mesi di vita sono stati testati in un compito di ricerca visiva di una figura illusoria. Tale procedura è comunemente utilizzata negli adulti per indagare se il binding percettivo degli elementi induttori di una figura illusoria sono indipendenti dall’attenzione selettiva spaziale o se, al contrario, il binding percettivo richiede l’intervento dell’attenzione (Davis & Driver, 1994). L’utilizzo di un eye tracker permette di utilizzare gli stessi stimoli e la stessa procedura per gli adulti e i bambini e, di conseguenza, di confrontare direttamente il comportamento visivo nelle due diverse età. Ai partecipanti sono state presentate una figura illusoria e una figura reale inserite in un display di elementi distrattori (Esperimenti 5-9). La percezione della figura illusoria era possibile solamente grazie al binding degli elementi induttori. L’analisi dei movimenti oculari ha permesso di evidenziare che sia la figura illusoria che la reale catturavano automaticamente l’attenzione degli adulti (i.e. effetto pop out), dimostrando così che il binding percettivo degli elementi induttori di una figura illusoria non richiede attenzione selettiva spaziale. Al contrario, i bambini hanno mostrato un effetto pop out solo quando un target reale percettivamente saliente è stato presentato all’interno del display (Esperimento 7). Invece, quando la ricerca visiva ha implicato la selezione di un target illusorio (Esperimenti 7 e 9), o quando è stato presentato un display in cui il target reale era percettivamente più simile ai distrattori, i bambini hanno orientato l’attenzione all’interno del display in maniera casuale, dimostrando che nei primi mesi di vita il binding percettivo di una figura illusoria non opera in modo analogo agli adulti. Complessivamente, i dati dimostrano che, sebbene i processi di binding percettivo (Espermenti 1-3) e di attenzione selettiva (Esperimento 4) supportino la percezione di una figura illusoria molto precocemente nel corso dello sviluppo, nei bambini di pochi mesi di vita il binding percettivo non opera in modo automatico come avviene negli adulti (Esperimenti 5-9). Questo risultato suggerisce che, nella prima infanzia, l’attenzione selettiva è un processo fondamentale per il binding percettivo delle caratteristiche di un oggetto, e che il modo in cui tale processo opera influisce sulla capacità del sistema visivo di raggruppare gli elementi di un oggetto in modo automatico, come dimostrato negli adulti

Professional actions of novice teachers in the context of teaching and learning geometry

International audienceThis paper aims to describe the professional actions of beginning teachers in the context of teaching and learning geometry. Using different theoretical tools, our research is based on the observation of lessons (with students aged between 6 and 11) delivered by beginning teachers in France. The paper seeks to show how the specific context of geometry impacts on professional actions especially among beginning teachers

Quels gestes professionnels d’enseignement au service d’une communauté discursive géométrique scolaire ?

Our work seeks to describe professional teaching actions in geometry classes. We rely on the analysis of a collection of observations of sessions in a 6th grade class (pupil ages 11–12 years) conducted by the same teacher during the same school year, based on a progression designed collectively and collaboratively within an IREM group. In our work, the study of the links between teaching and learning in the geometry class is examined through the relations between professional action and the School Mathematical Discursive Community.Notre travail cherche à décrire des gestes professionnels d’enseignement en classe de géométrie. Nous nous appuyons sur l’analyse d’un recueil d’observations de séances de classe de 6e menées par un même enseignant au cours d’une même année scolaire prenant appui sur une progression pensée collectivement et collaborativement au sein d’un groupe IREM. Dans notre travail, l’étude des liens entre enseignement et apprentissage en classe de géométrie est examinée à travers les relations entre gestes professionnels et Communauté Discursive Disciplinaire Scolaire

Étude des effets de la symétrie axiale sur la conceptualisation des isométries planes et sur la nature du travail géométrique au collège

Our study focuses on didactical effects of symmetry on teaching and learning of the others transformations of the plan at secondary school. We refer to Vergnaud's theory, the conceptual field theory and to the Houdement and Kuzniak's theoretical framework of geometrical paradigms and Geometrical Working Space (GWS) in order to describe the nature of geometrical work in student's activity. The main research question deals with the symmetry's play in the figural treatment, according to Duval meaning, in students' personal GWS. We propose a common test to the students at two different levels: at the second year (students are 12-13 years old), and at the fourth year of secondary school (students are 14-15 y. o.). This research points out that the personal GWS is more stabilized for a student at the end of secondary school than for a student at the beginning of secondary school. The schemes of the concept of symmetry are more flexible and can be adapted to the task. These symmetry's schemes contrast to the rotation's ones and reveal a different figural treatment according to the transformation at stake. Several analysis classrooms' practices from the same teacher at different levels at secondary school explain a part of these results from student's productions. Some schemes built in classroom reveal shift in meaning which seem negligible in classroom but crystallize students' practices. Our research concerns the nature of geometrical work in a vocational context too, through an investigation with craftsmen. This study describes how symmetry is a “naturalized” concept and how symmetry organizes craftsman's behaviour through geometry in action.Notre étude porte sur les effets didactiques de la symétrie axiale dans l'enseignement et l'apprentissage des transformations du plan au collège. Nous référons à la théorie des champs conceptuels de Vergnaud mais aussi au cadre des paradigmes géométriques et des Espaces de Travail Géométriques (ETG) de Houdement & Kuzniak afin de décrire la nature du travail géométrique en jeu dans l'activité de l'élève. Nous souhaitons déterminer le rôle de la symétrie axiale dans le type de déconstruction des figures, au sens de Duval, au cœur de l'ETG personnel des élèves. A partir de l'analyse d'un questionnaire commun en 5e et en 3e, il apparaît que la stabilité des ETG personnels des élèves de 3e est due à la souplesse d'adaptation des schèmes de la symétrie axiale selon la tâche. Cependant, ces schèmes semblent s'opposer à ceux liés à la rotation, et révèlent ainsi une appréhension des figures différentes selon la transformation en jeu. L'instabilité des ETG personnels des élèves de 5e se manifeste elle par de nombreux amalgames dus à la symétrie axiale. De nombreuses observations de classes en 6e, 5e et 3e d'un même professeur ont permis d'expliciter en partie ces résultats. Certains schèmes construits en classe révèlent des glissements qui semblent négligeables en classe mais se cristallisent ensuite dans les pratiques des élèves. Cette thèse rend également compte de la nature du travail géométrique dans une problématique pratique à travers une enquête auprès de tailleurs de pierre et ébénistes. Cette étude décrit comment la symétrie se révèle un concept « naturalisé » et organisateur de la conduite de l'artisan, dans le cadre d'une géométrie en acte organisée mais figée