Perceptual organization of auditory streaming-task relies on neural entrainment of the stimulus-presentation rate: MEG evidence

Background: Humans are able to extract regularities from complex auditory scenes in order to form perceptually meaningful elements. It has been shown previously that this process depends critically on both the temporal integration of the sensory input over time and the degree of frequency separation between concurrent sound sources. Our goal was to examine the relationship between these two aspects by means of magnetoencephalography (MEG). To achieve this aim, we combined time-frequency analysis on a sensor space level with source analysis. Our paradigm consisted of asymmetric ABA-tone triplets wherein the B-tones were presented temporally closer to the first A-tones, providing different tempi within the same sequence. Participants attended to the slowest B-rhythm whilst the frequency separation between tones was manipulated (0-, 2-, 4- and 10-semitones). Results: The results revealed that the asymmetric ABA-triplets spontaneously elicited periodic-sustained responses corresponding to the temporal distribution of the A-B and B-A tone intervals in all conditions. Moreover, when attending to the B-tones, the neural representations of the A- and B-streams were both detectable in the scenarios which allow perceptual streaming (2-, 4- and 10-semitones). Alongside this, the steady-state responses tuned to the presentation of the B-tones enhanced significantly with increase of the frequency separation between tones. However, the strength of the B-tones related steady-state responses dominated the strength of the A-tones responses in the 10-semitones condition. Conversely, the representation of the A-tones dominated the B-tones in the cases of 2- and 4-semitones conditions, in which a greater effort was required for completing the task. Additionally, the P1 evoked fields’ component following the B-tones increased in magnitude with the increase of inter-tonal frequency difference. Conclusions: The enhancement of the evoked fields in the source space, along with the B-tones related activity of the time-frequency results, likely reflect the selective enhancement of the attended B-stream. The results also suggested a dissimilar efficiency of the temporal integration of separate streams depending on the degree of frequency separation between the sounds. Overall, the present findings suggest that the neural effects of auditory streaming could be directly captured in the time-frequency spectrum at the sensor-space level.<br

How to improve learning from video, using an eye tracker

The initial trigger of this research about learning from video was the availability of log files from users of video material. Video modality is seen as attractive as it is associated with the relaxed mood of watching TV. The experiments in this research have the goal to gain more insight in viewing patterns of students when viewing video. Students received an awareness instruction about the use of possible alternative viewing behaviors to see whether this would enhance their learning effects. We found that: - the learning effects of students with a narrow viewing repertoire were less than the learning effects of students with a broad viewing repertoire or strategic viewers. - students with some basic knowledge of the topics covered in the videos benefited most from the use of possible alternative viewing behaviors and students with low prior knowledge benefited the least. - the knowledge gain of students with low prior knowledge disappeared after a few weeks; knowledge construction seems worse when doing two things at the same time. - media players could offer more options to help students with their search for the content they want to view again. - there was no correlation between pervasive personality traits and viewing behavior of students. The right use of video in higher education will lead to students and teachers that are more aware of their learning and teaching behavior, to better videos, to enhanced media players, and, finally, to higher learning effects that let users improve their learning from video

Natural scene statistics and the development of the primary visual cortex

Vision is the dominant human sensory modality. Due to the relative ease with which both visual input and visual brain areas can be studied and manipulated, vision has become an important window for enlarging our understanding of the biological sensory processing. Whether artificial or biological, visual processing systems must quickly and efficiently make sense of a large volume of noisy, high-dimensional input. To do this they construct statistical models of the input and utilise these models to efficiently encode visual scenes, detect features and construct a model of the world. In this thesis, we combine the study of natural scene statistics with mathematical models, experimental analysis and visual psychophysics to glean a deeper understanding of the development and function of the mammalian primary visual cortex. We start by considering functional models of receptive field development. We find, in agreement with previous work, that unsupervised learning models trained on natural scenes consistently learn that oriented ``edges'' (Gabor-like filters) are the basic features of natural scenes. The similarity between these filters and primary visual cortex receptive fields is strong evidence that primary visual cortex receptive fields are optimal encoders of visual input. We then significantly extend this work by comparing the prediction of unsupervised learning models with the receptive fields of animals reared in unusual visual environments. We find good agreement, which is evidence that aspects of receptive fields are learned during development, rather than innate. We also show that applying such unsupervised learning models to binocular visual input is not a simple extension of monocular visual input. Inter-ocular correlations change the optimal encoding strategy of binocular input so that it depends on edge orientation. Such functional models intriguingly predict an over-representation of vertically oriented receptive fields. After establishing that oriented edges are the basic feature of natural scenes and the unit of primary visual cortex receptive fields, we consider the statistics of edge arrangements in natural scenes. \citet{Sigman2001} showed that edges in natural scenes over short distances tend to be tangent to a common circle, or co-circular. Edge arrangements which contain a dependence between edge position and orientation may be said to have ``reduced symmetry'' as they lack a symmetry in that the edge position and orientation cannot be rotated independently without modifying the statistics of the arrangement. Co-circularity is one specific type of reduced symmetry. We extend previous work on natural scene co-circularity using a noise-resistant measure of co-circularity we develop and show that natural scenes contain significant co-circularity over extremely large angular distances ($>14\degree$). We also discuss preliminary work into variations in co-circularity statistics by scene type. After establishing that co-circularity is found pervasively in natural scenes, even over large distances, we then return to the structure of the primary visual cortex, but this time at the network level. Previous work has shown that, like edges in natural scenes, V1 orientation preferences maps also have reduced symmetry. However, the details of this dependence between orientation and position have not been examined in detail. We examine cat orientation preference maps from normal, stripe and blind-reared animals and find that, although orientation preference maps do contain reduced symmetry, it is not co-circularity. Moreover, the statistics of reduced symmetry in the maps are not affected by changes to visual input during development. Continuing our examination of V1 network structure, we consider the statistics of lateral connectivity in tree shrew V1. Previous work demonstrated that long-range V1 lateral connections are more common between regions with similar orientation preferences \citep{Bosking1997}. We re-examine this connectivity data using our noise-resistance measure of co-circularity. We find evidence that lateral connections between cells in the primary visual cortex may use two opposite wiring strategies which simultaneously facilitate quick processing of co-circular visual input while increasing the salience of the less expected deviations from co-circularity. Finally, we use the psychophysics of binocular rivalry to test whether co-circularity statistics can affect the functional processing of visual input in humans. We show, using binocular rivalry dominance as an objective measure of salience, that randomly arranged edges are more salient than edge arrangements which contain co-circularity. This is evidence that early visual processing may be functionally utilising edge arrangement statistics. In concurrence with our findings about lateral connections, this may indicate a general strategy of increasing the salience of unexpected visual input. Overall, we demonstrate that early visual coding uses natural scene statistics extensively. We show that oriented edges are a key currency in early visual processing. We find that the arrangement of edges in natural scenes contain rich statistical structure which influences wiring in the primary visual cortex during development and produces measurable changes in the salience of visual stimuli

Exploring the neural entrainment to musical rhythms and meter : a steady-state evoked potential approach

Thèse de doctorat réalisé en cotutelle avec l'Université catholique de Louvain, Belgique (Faculté de médecine, Institut de Neuroscience)Percevoir et synchroniser ses mouvements à une pulsation régulière en musique est une capacité largement répandue chez l’Homme, et fondamentale aux comportements musicaux. La pulsation et la métrique en musique désignent généralement une organisation temporelle périodique perçue à partir de stimuli acoustiques complexes, et cette organisation perceptuelle implique souvent une mise en mouvement périodique spontanée du corps. Cependant, les mécanismes neuraux sous-tendant cette perception sont à l’heure actuelle encore méconnus. Le présent travail a donc eu pour objectif de développer une nouvelle approche expérimentale, inspirée par l’approche électrophysiologique des potentiels évoqués stationnaires, afin d’explorer les corrélats neuraux à la base de notre perception de la pulsation et de la métrique induite à l’écoute de rythmes musicaux. L’activité neurale évoquée en relation avec la perception d’une pulsation a été enregistrée par électroencéphalographie (EEG) chez des individus sains, dans divers contextes : (1) dans un contexte d’imagerie mentale d’une métrique appliquée de manière endogène sur un stimulus auditif, (2) dans un contexte d’induction spontanée d’une pulsation à l’écoute de patterns rythmiques musicaux, (3) dans un contexte d’interaction multisensorielle, et (4) dans un contexte de synchronisation sensorimotrice. Pris dans leur ensemble, les résultats de ces études corroborent l’hypothèse selon laquelle la perception de la pulsation en musique est sous-tendue par des processus de synchronisation et de résonance de l’activité neurale dans le cerveau humain. De plus, ces résultats suggèrent que l’approche développée dans le présent travail pourrait apporter un éclairage significatif pour comprendre les mécanismes neuraux de la perception de la pulsation et des rythmes musicaux, et, dans une perspective plus générale, pour explorer les mécanismes de synchronisation neurale.The ability to perceive a regular beat in music and synchronize to it is a widespread human skill. Fundamental to musical behavior, beat and meter refer to the perception of periodicities while listening to musical rhythms, and usually involve spontaneous entrainment to move on these periodicities. However, the neural mechanisms underlying entrainment to beat and meter in Humans remain unclear. The present work tests a novel experimental approach, inspired by the steady-state evoked potential method, to explore the neural dynamics supporting the perception of rhythmic inputs. Using human electroencephalography (EEG), neural responses to beat and meter were recorded in various contexts: (1) mental imagery of meter, (2) spontaneous induction of a beat from rhythmic patterns, (3) multisensory integration, and (4) sensorimotor synchronization. Our results support the view that entrainment and resonance phenomena subtend the processing of musical rhythms in the human brain. Furthermore, our results suggest that this novel approach could help investigating the link between the phenomenology of musical beat and meter and neurophysiological evidence of a bias towards periodicities arising under certain circumstances in the nervous system. Hence, entrainment to music provides an original framework to explore general entrainment phenomena occurring at various levels, from the inter-neural to the inter-individual level

Kuwaiti Arabic: A Socio-Phonological Perspective

Diglossia manifests itself on various linguistic levels, one of which is phonological. It poses a linguistic ‘struggle’ for speakers in the Arab world through the functional distribution that exists between the Arabic language and its varieties. This is the main drive behind diglossia. These varieties are part of the same language; hence, the term ‘diglossic-switching’ is employed when describing the alternation of speakers from one level to another. The extreme functional dichotomy in treating diglossia, such as that of Ferguson (1959) High Level and Low Level has since been replaced with a more flexible and realistic interpretation, whereby the speech situation is to be seen as one of continuum constituting a gradient of speech levels co-existing between the two extreme poles: Modern Standard Arabic (H or acrolect) and the colloquial (L or basilect). First, this study examines diglossic switching in Kuwaiti Arabic along four main dialectal phonological variables. These are [č], [g], [j], and [y]. The occurrences of each of the four phonological variables are correlated concurrently with four sociolinguistic variables (age, gender, religious affiliation, and area~origin) and six recording groups (Duwāniyya ‘social gathering’ Group Observation, Semi-Structured Interview, Political Show, Kuwait National Assembly, and Xuṭba ‘religious sermon’) to which the respondents belong. A distribution and frequency analysis shows that there is a tight, dependant relation between the production of the dialectal features and sociological/recording groups. Further, a correlational and multivariate analysis shows that only ‘age’ correlates significantly (negatively) with 3 out 4 of the dialectal markers. Following this, the study constructs and defines the mid-levels in the dialect, and identifies Kuwaiti Modern Arabic as the mesolect, being a product of constant admixture between Modern Standard Arabic and Kuwaiti Arabic in a process of diglossic-switching. It is established that that the speech situation in Kuwait is a multiglossic one, where seven overlapping levels exist in a functionally-distributed sociolinguistic relationship

Temporal Processing in the Visual System

Encoding time is one of the most important features of the mammalian brain. The visual system, comprising almost half of the brain is of no exception. Time processing enables us to make goal-directed behavior in the optimum “time window” and launch a ballistic eye movement, reach/grasp an object or direct our processing resources (attention) from one point of interest to another. In addition, encoding time is critical for higher cognitive functions, enabling us to make causal inferences. The limitations of temporal individuation in the visual stream seem to vary across the visual field: the resolution gradually drops as objects become farther away from the center of gaze, where little differences were found in terms of resolution for objects in the upper versus lower visual field. This resolution of temporal individuation is vastly different from the resolution ascribed to spatial individuation. If individuation is mediated through attention, as some researchers have proposed, the general term ”attention” seems to possess different properties, at least regarding temporal and spatial processing. Next we looked at another aspect of encoding time: Temporal Order Judgments (TOJ), where animals had to judge the relative timing onset of two visual events. After training two monkeys on the task, we recorded from neurons in the lateral intraparietal area (LIP), while the animals reported the perceived order of two visual stimuli. We found that LIP neurons show differential activity based on the animal’s perceptual choice: when the animal reports the stimulus inside the receptive field of the neuron as first, the cells show an increased level of activity compared to when the animal reports he same stimulus as second. This differential activity was most reliable in the tonic period of the response $(\sim100 ms$ after stimulus onset). However, no difference in visual response latencies was observed between the different perceptual choices. The parietal cortex has previously been implicated in temporal processing based on patient studies as well as neuroimaging investigations. Physiological studies have also suggested the involvement of parietal area in encoding elapsed time. However, our study is the first to demonstrate parietal neurons encoding relative timing.Psycholog