Academic literature on the topic 'Visual dorsal stream'

Current evidence supports the view that the visual pulvinar of primates consists of at least five nuclei, with two large nuclei, lateral pulvinar ventrolateral (PLvl) and central lateral nucleus of the inferior pulvinar (PIcl), contributing mainly to the ventral stream of cortical processing for perception, and three smaller nuclei, posterior nucleus of the inferior pulvinar (PIp), medial nucleus of the inferior pulvinar (PIm), and central medial nucleus of the inferior pulvinar (PIcm), projecting to dorsal stream visual areas for visually directed actions. In primates, both cortical streams are highly dependent on visual information distributed from primary visual cortex (V1). This area is so vital to vision that patients with V1 lesions are considered “cortically blind”. When the V1 inputs to dorsal stream area middle temporal visual area (MT) are absent, other dorsal stream areas receive visual information relayed from the superior colliculus via PIp and PIcm, thereby preserving some dorsal stream functions, a phenomenon called “blind sight”. Non-primate mammals do not have a dorsal stream area MT with V1 inputs, but superior colliculus inputs to temporal cortex can be more significant and more visual functions are preserved when V1 input is disrupted. The current review will discuss how the different visual streams, especially the dorsal stream, have changed during primate evolution and we propose which features are retained from the common ancestor of primates and their close relatives.

Object and depth perception from motion cues involves the recruitment of visual dorsal stream brain areas. In 3-D structure-from-motion (SFM) perception, motion and depth information are first extracted in this visual stream to allow object categorization, which is in turn mediated by the ventral visual stream. Such interplay justifies the use of SFM paradigms to understand dorsal–ventral integration of visual information. The nature of such processing is particularly interesting to be investigated in a neurological model of cognitive dissociation between dorsal (impaired) and ventral stream (relatively preserved) processing, Williams syndrome (WS). In the current fMRI study, we assessed dorsal versus ventral stream processing by using a performance-matched 3-D SFM object categorization task. We found evidence for substantial reorganization of the dorsal stream in WS as assessed by whole-brain ANOVA random effects analysis, with subtle differences in ventral activation. Dorsal reorganization was expressed by larger medial recruitment in WS (cuneus, precuneus, and retrosplenial cortex) in contrast with controls, which showed the expected dorsolateral pattern (caudal intraparietal sulcus and lateral occipital cortex). In summary, we found a substantial reorganization of dorsal stream regions in WS in response to simple visual categories and 3-D SFM perception, with less affected ventral stream. Our results corroborate the existence of a medial dorsal pathway that provides the substrate for information rerouting and reorganization in the presence of lateral dorsal stream vulnerability. This interpretation is consistent with recent findings suggesting parallel routing of information in medial and lateral parts of dorsal stream.

Recent reports have documented greater plasticity in the dorsal visual stream as compared with the ventral visual stream. This study sought to test the hypothesis that this greater plasticity may be related to a more protracted period of development in the dorsal as compared with the ventral stream. Age-related effects on event-related potentials (ERPs) elicited by motion and color stimuli, designed to activate the two visual streams, were assessed in healthy individuals aged 6 years through adulthood. Although significant developmental effects were observed in amplitudes of ERPs to both color and motion stimuli, marked latency effects were observed only in response to motion. These results provide support for the hypothesis that the dorsal stream displays a longer developmental time course across the early school years than the ventral stream. Implications for neural and behavioral plasticity are discussed.

Conventional imaging methods could not distinguish processes within the ventral and dorsal streams. The application of Fourier time series analysis was helpful to segregate changes in the ventral and dorsal streams of the visual system in male and female mice. The present study measured the accumulation of [18F]fluorodeoxyglucose ([18F]FDG) in the mouse brain using small animal positron emission tomography and magnetic resonance imaging (PET/MRI) during light stimulation with blue and yellow filters, compared to during conditions of darkness. Fourier analysis was performed using mean standardized uptake values (SUV) of [18F]FDG for each stimulus condition to derive spectral density estimates for each condition. In male mice, luminance opponency occurred by S-peak changes in the sub-cortical retino-geniculate pathways in the dorsal stream supplied by ganglionic arteries in the left visual cortex, while chromatic opponency involved C-peak changes in the cortico-subcortical pathways in the ventral stream perfused by cortical arteries in the left visual cortex. In female mice, there was resonance phenomenon at C-peak in the ventral stream perfused by the cortical arteries in the right visual cortex during luminance processing. Conversely, chromatic opponency caused by S-peak changes in the subcortical retino-geniculate pathways in the dorsal stream supplied by the ganglionic arteries in the right visual cortex. In conclusion, Fourier time series analysis uncovered distinct mechanisms of color processing in the ventral stream in males, while in female mice color processing was in the dorsal stream. It demonstrated that computation of colour processing as a conscious experience could have a wide range of applications in neuroscience, artificial intelligence and quantum mechanics.

Deictic coding offers a useful model for understanding the interactions between the dorsal and ventral streams of visual processing in the cerebral cortex. By extending Ballard et al.'s ideas on teleassistance, I show how dedicated low-level visuomotor processes in the dorsal stream might be engaged for the services of high-level cognitive operations in the ventral stream.

Growing evidence suggests that the functional specialization of the two cortical visual pathways may not be as distinct as originally proposed. Here, we explore possible contributions of the dorsal “where/how” visual stream to shape perception and, conversely, contributions of the ventral “what” visual stream to location perception in human adults. Participants performed a shape detection task and a location detection task while undergoing fMRI. For shape detection, comparable BOLD activation in the ventral and dorsal visual streams was observed, and the magnitude of this activation was correlated with behavioral performance. For location detection, cortical activation was significantly stronger in the dorsal than ventral visual pathway and did not correlate with the behavioral outcome. This asymmetry in cortical profile across tasks is particularly noteworthy given that the visual input was identical and that the tasks were matched for difficulty in performance. We confirmed the asymmetry in a subsequent psychophysical experiment in which participants detected changes in either object location or shape, while ignoring the other, task-irrelevant dimension. Detection of a location change was slowed by an irrelevant shape change matched for difficulty, but the reverse did not hold. We conclude that both ventral and dorsal visual streams contribute to shape perception, but that location processing appears to be essentially a function of the dorsal visual pathway.

Visual processing of complex objects is supported by the ventral visual pathway in the service of object identification and by the dorsal visual pathway in the service of object-directed reaching and grasping. Here, we address how these two streams interact during tool processing, by exploiting the known asymmetry in projections of subcortical magnocellular and parvocellular inputs to the dorsal and ventral streams. The ventral visual pathway receives both parvocellular and magnocellular input, whereas the dorsal visual pathway receives largely magnocellular input. We used fMRI to measure tool preferences in parietal cortex when the images were presented at either high or low temporal frequencies, exploiting the fact that parvocellular channels project principally to the ventral but not dorsal visual pathway. We reason that regions of parietal cortex that exhibit tool preferences for stimuli presented at frequencies characteristic of the parvocellular pathway receive their inputs from the ventral stream. We found that the left inferior parietal lobule, in the vicinity of the supramarginal gyrus, exhibited tool preferences for images presented at low temporal frequencies, whereas superior and posterior parietal regions exhibited tool preferences for images present at high temporal frequencies. These data indicate that object identity, processed within the ventral stream, is communicated to the left inferior parietal lobule and may there combine with inputs from the dorsal visual pathway to allow for functionally appropriate object manipulation.

Action video games foster competitive environments that demand rapid spatial navigation and decision-making. Action video gamers often exhibit faster response times and slightly improved accuracy in vision-based sensorimotor tasks. Background/Objectives: However, the underlying functional and structural changes in the two visual streams of the brain that may be contributing to these cognitive improvements have been unclear. Methods: Using functional and diffusion MRI data, this study investigated the differences in connectivity between gamers who play action video games and nongamers in the dorsal and ventral visual streams. Results: We found that action video gamers have enhanced functional and structural connectivity, especially in the dorsal visual stream. Specifically, there is heightened functional connectivity—both undirected and directed—between the left superior occipital gyrus and the left superior parietal lobule during a moving-dot discrimination decision-making task. This increased connectivity correlates with response time in gamers. The structural connectivity in the dorsal stream, as quantified by diffusion fractional anisotropy and quantitative anisotropy measures of the axonal fiber pathways, was also enhanced for gamers compared to nongamers. Conclusions: These findings provide valuable insights into how action video gaming can induce targeted improvements in structural and functional connectivity between specific brain regions in the visual processing pathways. These connectivity changes in the dorsal visual stream underpin the superior performance of action video gamers compared to nongamers in tasks requiring rapid and accurate vision-based decision-making.

Due to various shortcomings of the visual system, some visual stimuli can only be identified with 100% accuracy if they are shown for a certain amount of time. This time can be measured using the Inspection Time (IT) paradigm. In an IT task, a “pi” figure with differing leg lengths is typically presented briefly (e.g., 20-200 ms) and is then immediately masked to prevent retinal afterimages. Participants are subsequently required to choose which of the two legs was longer. The objective of this task is to determine the shortest amount of time the pi figure needs to be shown for it to be perceived with 80% accuracy. Given that visual processing has been shown to be altered during and /or prior to a movement, the present experiment sought to test how the requirement to perform a motor task affected IT. Twenty-eight participants took part in the experiment, which was comprised of three conditions: no-movement (NM), peak velocity (PV), and foreperiod (FP). In the NM condition, participants grasped a manipulandum and engaged in the IT paradigm. At the end of every trial, participants verbally stated which leg they believed was longest. In the PV condition participants made a rapid movement to a target, and the IT stimulus was presented when their limb reached peak velocity. Finally in the FP condition the IT stimulus was presented during foreperiod (FP). In all three conditions the IT stimulus was randomly presented from between 15-105 ms (in 15 ms increments) and masked for 400 ms. Results showed no significant differences on the IT task between the NM and FP conditions, suggesting no visual upregulation during foreperiod. However, IT performance was significantly poorer in the PV condition in comparison to both the NM and FP condition, suggesting a visual downregulation at that particular movement kinematic.

Il a été établi que les troubles de la perception visuo-spatiale étaient fréquents dans la population d’enfants présentant des troubles des apprentissages et que 60% des enfants avec un trouble du neuro-développement ont un déficit de perception visuo-spatiale élémentaire (PVSE). Notre objectif en réalisant ce travail était double. D’une part un objectif de recherche fondamentale : mieux comprendre le rôle que joue la vision dans la cognition spatiale. Et d’autre part, un objectif clinique : mieux comprendre les déficits du développement de la PVSE et leurs conséquences fonctionnelles dans des contextes dans lesquels ils ne sont pas suffisamment pris en considération. Ainsi, nous avons évalué la prévalence des troubles de la PVSE chez des enfants présentant un déficit moteur dans le contexte d’une Paralysie cérébrale. Nous avons constaté que le développement de la PVSE était plus déficitaire avec une lésion cérébrale dans le contexte de la prématurité que dans le cas d’une lésion néonatale. Pour une meilleure compréhension de ce phénomène, nous nous sommes intéressés aux enfants nés prématurés sans lésion cérébrale qui consultent pour des troubles des apprentissages. Nous avons constaté que même en l’absence de trouble du neuro-développement, la prématurité était un facteur de risque supplémentaire de développer des troubles de la PVSE et notamment de la perception des grandeurs. Ces deux études laissent penser qu’un déficit de la PVSE serait lié au développement cérébral intra-utérin et serait indépendant de l’environnement dans lequel se réalise la maturation post-natale du cortex. Mais quel est le rôle que jouent les entrées sensorielles dans la perception et la cognition spatiale ? La littérature s’est principalement intéressée aux cécités congénitales et leur impact sur la cognition spatiale soulignant que la vision ne serait pas juste une modalité d’entrée comme une autre mais qu’elle interviendrait de façon cruciale dans le développement de la cognition spatiale. Peu de travaux ont évalué l’impact d’un déficit visuel partiel et progressif sur la perception spatiale, sur entrée visuelle ou non-visuelle, et sur la cognition spatiale et numérique. Nous avons montré une prévalence importante des troubles de la PVSE chez les personnes déficientes visuelles mais pas aveugles, et davantage en l’absence de champ visuel périphérique qu’en situation de baisse d’acuité visuelle. Ce constat est d’autant plus surprenant que nous avons démontré une absence de déficit de PVSE lors d’une étude évaluant le rôle de la vision périphérique chez des sujets sains. Ce déficit n’est donc pas lié à la saisie de l’information visuelle (qui peut être simulée expérimentalement chez le sujet sain) mais lié à un processus de plasticité maladaptative chez les patients, associé à l’atteinte chronique du champ visuel périphérique (une réorganisation corticale des aires visuelles ayant été démontrée en cas de rétinite pigmentaire). Nous avons constaté par ailleurs que ces patients développent moins de compensations haptiques et qu’ils sont en difficulté sur des tâches d’imagerie mentale. L’ensemble des déficients visuels montraient des difficultés en arithmétique mais pas à nos tâches de cognition numérique non-visuelle (sauf en cas de cécité congénitale), ce qui souligne l’importance d’utiliser des supports non-visuels pour apprendre et évaluer les compétences mathématiques chez les déficients visuels. La prise en compte des déficits de la PVSE est d’autant plus importante que les populations que nous avons étudiées sont plus à risque d’avoir des troubles dans les apprentissages et des échecs scolaires. À partir de ces travaux, nous pourrons envisager des prises en charges préventives adaptées et ne pas attendre l’échec scolaire pour agir
It was established that visuo-spatial perception troubles were frequent in children with learning disabilities and that 60% of children with neuro-developmental disabilities have a deficit of elementary visuo-spatial perception (EVSP). We had a double objective in this phD. The first one was for fundamental research: to understand more clearly the role that the vision plays in spatial cognition. The second objective was clinical: to understand more clearly the EVSP developmental deficit and its functional consequences in contexts where it is not taken into consideration enough. So, we evaluated the prevalence of EVSP troubles in children with a motor deficit in the context of cerebral palsy. Our results showed that the development of the EVSP was more problematic with brain damage in the context of prematurity than in the context of neonatal lesion. To better understand this phenomenon, we also tested EVSP in children born prematurely without cerebral lesion but with scholar complaints. We found that even without neuro-developmental disabilities, prematurity upgrades the risk of developing EVSP deficit, and particularly hinders length perception. These two studies made us think that EVSP deficit would be linked to cerebral intra-utero development and would be independent of the environment of postnatal maturation of the cortex. But what about the role of the sensory inputs in the development of spatial abilities? The literature has mainly been focused on congenital blindness and its impact on spatial cognition, highlighting that vision appears as a privileged modality in the development of spatial cognition. Few studies have evaluated the impact of partial and progressive visual impairment on spatial perception, tested in the visual or non-visual modality, and on spatial and numerical cognition. We demonstrated an important prevalence of EVSP troubles in visually impaired people with residual vision, more in the population with reduced peripheral visual field than in the population with decreased visual acuity. This finding contrasts with the demonstration that simulating a deficit of peripheral vision with gaze-contingent masking in healthy controls did not impact the EVSP accuracy. Altogether, this put forward that the EVSP deficit in patients with peripheral vision deficit is not linked to the restricted capture of visual information (that can be experimentally stimulated in healthy subjects) but is rather linked to a process of maladaptive plasticity, associated to the chronic lack of sensory input from peripheral vision (a reorganization of cortical visual areas has been demonstrated in neuroimaging for patients with retinitis pigmentosa). We have also found that these patients tend to develop less haptic compensations and to have more difficulties in mental imagery task. While all groups of visually impairment had difficulties in arithmetic, none, except people with congenital blindness, struggled in our non-visual numerical cognition tasks involving pointing toward a mental number line or bimanual magnitude estimation. This highlights the importance of using non-visual media to learn and evaluate the mathematical skills in visually impaired people. Accounting for EVSP deficits is important in the populations studied in this phD because they are at greater risk of learning disabilities and academic failure. Based on these studies, we can think at adapted preventive care and should not wait for academic failure to react

L'objectif de ces travaux a été d'étudier, à partir des potentiels évoqués, l'implication des voies ventrale (qui sous-tend le traitement expert de l'écrit) et dorsale (qui sous-tend des processus phonologiques et attentionnels) lors de la reconnaissance visuelle des mots chez des adultes dyslexiques. Les spécificités des sujets dyslexiques ont été isolées en les comparant à deux groupes contrôles, appariés sur : l'âge (i.e., des lecteurs experts) et sur le niveau de lecture (i.e., des mauvais lecteurs). Les résultats montrent des déficits du traitement expert de l'écrit, phonologiques et de la détection du conflit spécifiques aux sujets dyslexiques. Nos données montrent aussi des déficits du traitement expert des mots familiers et d'orientation de l'attention communs aux sujets dyslexiques et mauvais lecteurs. Les résultats sont discutés dans le cadre du modèle LCD, de la théorie du mapping phonologique et d'une implication précoce de l'orientation attentionnelle dans la lecture.

Tese de doutoramento em Ciências da Saúde, Ramo de Ciências Biomédicas, apresentada à Faculdade de Medicina da Universidade de Coimbra
O Síndrome de Williams (SW) é uma perturbação genética rara do neurodesenvolvimento caracterizada por alterações sensoriais, cognitivas e neuroanatómicas. Esta patologia constitui, por isso, um modelo ímpar para investigar a natureza modular (ou não) dos processos cognitivos, dado que proporciona uma oportunidade rara de estudo das relações entre genes, cérebro e comportamento. O SW tem suscitado interesse no domínio das neurociências cognitivas, devido ao seu perfil cognitivo peculiar, caracterizado por funções preservadas no domínio da linguagem e do reconhecimento facial em oposição a consideráveis défices de coerência visual e de perceção visuo-espacial. No SW verifica-se um viés a favor do processamento visual local, falhando ao mesmo tempo na integração desta informação local que é determinante para a perceção de coerência global. Estas dissociações funcionais no domínio cognitivo têm sido estudadas a par com dissociações ao nível do funcionamento neuronal particularmente no que diz respeito às vias de processamento visual dorsal e ventral. Contudo, o debate persiste e os correlatos neuroanatómicos e neurofisiológicos destes défices não estão ainda estabelecidos. O foco desta tese prende-se com a investigação de múltiplos níveis de processamento visual associados às vias dorsal e ventral no SW, com especial enfoque nas dissociações funcionais encontradas nesta patologia. Nestas incluem-se as dicotomias funcionais entre as vias dorsal vs. ventral, o processamento local vs. global e as representações egocêntricas vs. alocêntricas, bem como as relações entre eles. O estudo destas dicotomias é relevante no SW pois este é um modelo neurobiológico de dissociação entre as vias visuais ventral e dorsal, caracterizada por um défice acentuado desta última. Nesta tese foram usadas de forma complementar múltiplos métodos tais como a psicofísica, eletrofisiologia bem como neuroimagem funcional com vista a melhor caracterizar os défices visuo-espaciais no SW e elucidar em que medida os seus correlatos neuronais se prendem com o funcionamento das vias dorsal e ventral. Neste trabalho, a coerência visual foi extensivamente investigada no SW através da avaliação do processamento visual local e global sob várias condições experimentais (perceção, memória e capacidade visuo-construtiva) comparando com as perturbações do espectro do autismo (PEA), que têm sido associadas a défices de coerência visual, do processamento local vs. global e do funcionamento da via dorsal. O nosso primeiro estudo confirmou o SW como um modelo clínico de coerência visual diminuída, mostrando que estes défices são mais severos nesta patologia do que nas PEA sugerindo o envolvimento da via dorsal (mais afectada no SW) neste tipo de processamento. O estudo da dissociação entre as vias dorsal e ventral no SW foi aprofundado, no segundo estudo, usando um novo paradigma experimental no qual investigámos representações espaciais egocêntricas (associadas à via dorsal) e alocêntricas (associadas à via ventral) no SW. Desenvolvemos uma tarefa experimental em computador e outra utilizando um tabuleiro (com maior validade ecológica). Ambos os tipos de representação espacial se mostraram alteradas no grupo de SW. Para além de confirmarem défices na via visual dorsal no SW (representações egocêntricas), os nossos resultados revelaram alterações inesperadas nas representações espaciais alocêntricas sugerindo que a via ventral pode também estar afetada nesta condição. Uma vez confirmado que o grupo de SW constitui um modelo clínico de coerência visual diminuída e alterações da via dorsal, realizámos dois estudos adicionais, com vista a estabelecer os correlatos neuronais dos défices de coerência visual no SW. Devido ao seu carácter complementar, estes estudos usaram respetivamente eletroencefalografia (EEG) e ressonância magnética funcional (RMF). A perceção de coerência foi avaliada com uma tarefa de perceção de estrutura tridimensional através do movimento na qual modulámos a informação de profundidade. Os dados de EEG revelaram padrões distintos entre os grupos, sugerindo uma organização neuronal alternativa no SW. Um novo componente, o P200, foi observado somente para este grupo e foram observadas diferentes fontes neuronais, sobretudo localizadas no lobo occipital por contraste às fontes parietais encontradas nos controlos. A elevada resolução espacial da RMF permitiu ao estudo subsequente uma melhor localização dos correlatos neuronais desta reorganização. Verificou-se que, enquanto os controlos ativam as áreas dorso-laterais esperadas (sulco intraparietal caudal e córtex occipital lateral/hMT+), os indivíduos com SW recrutam áreas mais mediais (cuneus, precuneus e córtex retrosplenial) em resposta aos estímulos coerentes em 3D, mas também a imagens estáticas de várias categorias visuais e movimento coerente simples (2D). A ativação em zonas mais mediais do cérebro observada no grupo de SW sugere uma reorganização substancial das regiões da via dorsal, com o processamento de movimento a ocorrer na parte medial desta via. Não encontrámos diferenças entre os grupos no que respeita à via ventral, não obstante ligeiras alterações nos padrões de ativação entre os grupos que poderão indicar que esta via não está tão preservada quanto o esperado. O trabalho aqui apresentado demonstra défices de coerência visual no SW que estão associados à disfunção da via dorsal, avaliada em múltiplos níveis visuais. A reorganização substancial da via dorsal observada no SW pode levar a alterações na via visual ventral, como sugerido pelos nossos estudos. Estes resultados contribuem para o conhecimento relativo à natureza das dissociações funcionais (dorsal/ventral, ego/alo e local/global) no SW e proporcionam um avanço no nosso entendimento dos mecanismos de processamento visual que ocorrem na via dorsal.
Williams syndrome (WS) is a rare genetically based neurodevelopmental condition associated with a unique combination of sensory, cognitive and neuroanatomical characteristics. This condition is, therefore, an outstanding model to understand cognition because it provides a rare opportunity to investigate genes, brain and behaviour relationships. WS has captured the interest of cognitive neuroscientists in the last decades, mainly because of its intriguing cognitive profile characterized by surprising spared language and face abilities contrasting with severe deficits in visuospatial skills and visual coherence. These patients tend to exhibit a visual bias towards local processing while failing to achieve global coherence from the integration of local cues. Functional dissociations in the cognitive domain have been concomitantly investigated at the neural level in particular in which concerns both dorsal and ventral visual processing pathways. However, the existing literature on this topic has not yet settled this issue and the neurophysiological and neuroanatomical correlates of such impairments remain unclear. The main focus of this thesis is the investigation of multiple levels of visual processing along dorsal and ventral visual pathways in WS, from the point of view of functional dissociations. These include dorsal vs. ventral, local vs. global, ego vs. allocentric processing dichotomies and their relationships. This is particularly relevant, since this condition is a neurobiological model of a split between ventral and dorsal visual processing pathways with a generalized deficit in dorsal pathway. The combination of multiple methodological modalities such as psychophysics, electrophysiology and neuroimaging tools is conducted in this thesis to allow a better characterization of the visuospatial impairments in WS and elucidate on how the neural correlates of such vulnerabilities relate to dorsal and ventral functioning. In the first study of this thesis, visual coherence perception in WS was comprehensively investigated by probing the local-global visual processing under different task conditions (Navon hierarchical figures under perception, memory and visuoconstructive conditions) and performing a direct comparison to autism spectrum disorders (ASD) in which visual coherence weakness was also suggested, along with local vs. global and dorsal stream deficits. We confirmed the WS group as a clinical model of impaired visual coherence. These impairments were shown in WS to a larger extent than in ASD which may suggest the involvement of the dorsal visual stream (more impaired in WS than in ASD) in such perceptual mechanisms. We further investigated the dorsal vs. ventral stream dissociation in WS by employing a novel paradigm in which dichotomic egocentric (associated with dorsal stream) and allocentric (associated with ventral stream) spatial frames of reference were investigated. A computer judgment task as well as a more ecological 3D judgment task (using a board) was used. Our findings confirmed dorsal stream vulnerability in the WS group as assessed by egocentric spatial judgments. We also found unexpected impaired allocentric spatial judgments in WS suggesting that ventral visual stream may also be compromised. Given that the aforementioned findings confirm WS as a suitable clinical model of coherence impairment and dorsal stream vulnerability (alongside with possible slightly affected ventral stream function), we conducted two additional studies to investigate neural correlates of visual coherence impairment in WS. These studies were accomplished using electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI). We used a three-dimensional (3D) structure-from-motion (SFM) task in order to assess coherent perception in which we parametrically modulated depth information. EEG data revealed distinct patterns across groups, suggesting functional reorganization in WS. We observed a novel component P200 present only in the clinical group as well as differential neural sources in occipital sites in contrast to parietal sources in controls. The fMRI study, due to its higher spatial resolution, allowed us to pinpoint the neural correlates of such reorganization. Individuals with WS recruited more medial areas (cuneus, precuneus and retrosplenial cortex) in response to 3D coherent stimuli, high-level visual object categories and simple coherent motion in contrast with typically developing controls who showed, as expected, more lateral areas (caudal intraparietal sulcus and lateral occipital cortex/hMT+). This shift to the midline we observed in the WS group pattern of activation suggests a substantial reorganization of dorsal stream regions with predominant motion processing occurring in the medial part of this visual pathway. We did not identify significant group differences regarding the ventral visual modulation. However, subtle alterations in the pattern of activation across groups were found indicating that ventral visual stream may not be as preserved as traditionally defined. In sum, the work presented in this thesis demonstrate visual coherence impairments in WS which are associated with dorsal stream dysfunction as was assessed by multiple visual levels. The substantial reorganization of dorsal stream observed in our EEG and fMRI studies may contribute to alterations in the ventral visual stream which already demonstrated slight vulnerabilities. These findings improve our knowledge concerning the nature of functional dissociations (dorsal/ventral, ego/allo and local/global) in WS and provide insight on the mechanisms of visual processing within the dorsal stream.

Congenital hypothyroidism (CH), a pediatric endocrine condition that results in early thyroid hormone (TH) insufficiency, is associated with visuospatial dysfunction suggestive of selective dorsal visual stream impairment. However, the ventral visual stream has not been adequately investigated in this population and so the effect of early TH insufficiency on development of the two streams had not been clearly established. This thesis used a comprehensive set of neuropsychological and experimental tests to assess higher-order visual functions in children and adolescents with CH compared with typically developing individuals. The results show that while CH is associated with poorer performance on tasks tapping into dorsal stream functions such as judgment of line orientation, spatial localization, three-dimensional block and two-dimensional mental construction, judgment of object location, and mental rotation, performance on typical ventral stream tasks such as identity discrimination, including abstract shapes, faces, and buildings, is relatively unimpaired. Thus this thesis establishes that the dorsal visual stream is selectively vulnerable to TH insufficiency. In addition to the investigating the nature of the higher-order visual problems in CH, this thesis explores the mechanism underlying these problems and assesses whether they result from organizational effects by early TH or activational effects by current TH levels. The data support the organizational mechanism and suggest that prenatal TH insufficiency results in irreversible changes to the dorsal visual stream due to the timing of dorsal stream development, which occurs earlier than ventral stream development and is thus more vulnerable to insult.

abstract: The present study explores the role of motion in the perception of form from dynamic occlusion, employing color to help isolate the contributions of both visual pathways. Although the cells that respond to color cues in the environment usually feed into the ventral stream, humans can perceive motion based on chromatic cues. The current study was designed to use grey, green, and red stimuli to successively limit the amount of information available to the dorsal stream pathway, while providing roughly equal information to the ventral system. Twenty-one participants identified shapes that were presented in grey, green, and red and were defined by dynamic occlusion. The shapes were then presented again in a static condition where the maximum occlusions were presented as before, but without motion. Results showed an interaction between the motion and static conditions in that when the speed of presentation increased, performance in the motion conditions became significantly less accurate than in the static conditions. The grey and green motion conditions crossed static performance at the same point, whereas the red motion condition crossed at a much slower speed. These data are consistent with a model of neural processing in which the main visual systems share information. Moreover, they support the notion that presenting stimuli in specific colors may help isolate perceptual pathways for scientific investigation. Given the potential for chromatic cues to target specific visual systems in the performance of dynamic object recognition, exploring these perceptual parameters may help our understanding of human visual processing.
Dissertation/Thesis
M.A. Psychology 2011

En raison de l’utilisation d’un mode de communication totalement différent de celui des entendants, le langage des signes, et de l’absence quasi-totale d’afférences en provenance du système auditif, il y a de fortes chances que d’importantes modifications fonctionnelles et structurales s’effectuent dans le cerveau des individus sourds profonds. Les études antérieures suggèrent que cette réorganisation risque d’avoir des répercussions plus importantes sur les structures corticales situées le long de la voie visuelle dorsale qu’à l’intérieur de celles situées à l’intérieur de la voie ventrale. L’hypothèse proposée par Ungerleider et Mishkin (1982) quant à la présence de deux voies visuelles dans les régions occipitales, même si elle demeure largement acceptée dans la communauté scientifique, s’en trouve aussi relativement contestée. Une voie se projetant du cortex strié vers les régions pariétales postérieures, est impliquée dans la vision spatiale, et l’autre se projetant vers les régions du cortex temporal inférieur, est responsable de la reconnaissance de la forme. Goodale et Milner (1992) ont par la suite proposé que la voie dorsale, en plus de son implication dans le traitement de l’information visuo-spatiale, joue un rôle dans les ajustements sensori-moteurs nécessaires afin de guider les actions. Dans ce contexte, il est tout à fait plausible de considérer qu’un groupe de personne utilisant un langage sensori-moteur comme le langage des signes dans la vie de tous les jours, s’expose à une réorganisation cérébrale ciblant effectivement la voie dorsale. L’objectif de la première étude est d’explorer ces deux voies visuelles et plus particulièrement, la voie dorsale, chez des individus entendants par l’utilisation de deux stimuli de mouvement dont les caractéristiques physiques sont très similaires, mais qui évoquent un traitement relativement différent dans les régions corticales visuelles. Pour ce faire, un stimulus de forme définie par le mouvement et un stimulus de mouvement global ont été utilisés. Nos résultats indiquent que les voies dorsale et ventrale procèdent au traitement d’une forme définie par le mouvement, tandis que seule la voie dorsale est activée lors d’une tâche de mouvement global dont les caractéristiques psychophysiques sont relativement semblables. Nous avons utilisé, subséquemment, ces mêmes stimulations activant les voies dorsales et ventrales afin de vérifier quels pourraient être les différences fonctionnelles dans les régions visuelles et auditives chez des individus sourds profonds. Plusieurs études présentent la réorganisation corticale dans les régions visuelles et auditives en réponse à l’absence d’une modalité sensorielle. Cependant, l’implication spécifique des voies visuelles dorsale et ventrale demeure peu étudiée à ce jour, malgré plusieurs résultats proposant une implication plus importante de la voie dorsale dans la réorganisation visuelle chez les sourds. Suite à l’utilisation de l’imagerie cérébrale fonctionnelle pour investiguer ces questions, nos résultats ont été à l’encontre de cette hypothèse suggérant une réorganisation ciblant particulièrement la voie dorsale. Nos résultats indiquent plutôt une réorganisation non-spécifique au type de stimulation utilisé. En effet, le gyrus temporal supérieur est activé chez les sourds suite à la présentation de toutes nos stimulations visuelles, peu importe leur degré de complexité. Le groupe de participants sourds montre aussi une activation du cortex associatif postérieur, possiblement recruté pour traiter l’information visuelle en raison de l’absence de compétition en provenance des régions temporales auditives. Ces résultats ajoutent aux données déjà recueillies sur les modifications fonctionnelles qui peuvent survenir dans tout le cerveau des personnes sourdes, cependant les corrélats anatomiques de la surdité demeurent méconnus chez cette population. Une troisième étude se propose donc d’examiner les modifications structurales pouvant survenir dans le cerveau des personnes sourdes profondes congénitales ou prélinguales. Nos résultats montrent que plusieurs régions cérébrales semblent être différentes entre le groupe de participants sourds et celui des entendants. Nos analyses ont montré des augmentations de volume, allant jusqu’à 20%, dans les lobes frontaux, incluant l’aire de Broca et d’autres régions adjacentes impliqués dans le contrôle moteur et la production du langage. Les lobes temporaux semblent aussi présenter des différences morphométriques même si ces dernières ne sont pas significatives. Enfin, des différences de volume sont également recensées dans les parties du corps calleux contenant les axones permettant la communication entre les régions temporales et occipitales des deux hémisphères.
Due to the use of a mode of communication completely different from hearing people, Due to [the use of] a communication mode completely different from hearing people, the sign language and the absence of afferences from the auditory system, it is likely that significant functional and structural changes take place in the brains of profoundly deaf individuals. Previous studies suggest this reorganization may have greater impact on cortical structures located along the dorsal visual pathway than within the regions located inside the ventral pathway. The hypothesis, widely accepted by the scientific community, proposed by Ungerleider and Mishkin (1982) for the presence of two visual pathways in the occipital regions is also fairly contested. According to this hypothesis, one stream projecting from the striate cortex to the posterior parietal regions is involved in spatial vision and a second stream projecting to regions of the inferior temporal cortex underlying form recognition. Goodale and Milner (1992) subsequently proposed that the dorsal pathway, in addition to its involvement in the processing of visuospatial information, takes part in the necessary sensorymotor adjustments to guide actions. In this context, it is plausible to consider that a group of people using sensorimotor language (e.g., sign language) in their everyday life, the cerebral reorganization is more suited to target the dorsal pathway. The first objective of the study is to explore both visual pathways, especially the dorsal pathway, in hearing subjects by the use of two similar motion stimuli that evoke different types of processing. This was done with a form-from-motion stimuli and a global motion stimuli. Our results indicate that both dorsal and ventral pathways process forms defined by motion, while only the dorsal pathway is activated during a task of global motion whose psychophysical characteristics are relatively similar. Subsequently, we used these stimuli to activate the dorsal and ventral stream to investigate functional differences in the visual and auditory brain regions in profoundly deaf individuals. Several studies show cortical reorganization in the visual and auditory areas in response to the absence of a sensory modality. However, few studies have explored the specific involvement of dorsal and ventral visual streams, despite several results suggesting greater involvement of the dorsal pathway in visual reorganization with the deaf population. Following the use of functional brain imaging to investigate these issues, our results differed from the hypothesis suggesting a reorganization specifically targeting the dorsal pathway. Rather, our results indicate a non-specific reorganization to the different types of stimulations used. Indeed, the superior temporal gyrus was activated with the deaf following the presentation of our visual stimuli, regardless of their complexity. The group of deaf participants also showed activation of the posterior association cortex, possibly recruited to process visual information in the absence of competition from the temporal auditory regions. These results add to data already collected on the functional changes that may occur throughout the brains of deaf people, however, the anatomical correlates of deafness remains unknown in this population. A third study aimed to explore the structural changes occurring in the brains of prelingual and congenital profoundly deaf. Our results show that several brain regions appear to be different between the groups of participants composed of the deaf and hearing. Our analysis showed volume increases of up to 20% in the frontal lobe, including Broca's area and adjacent regions involved in motor control and language production. The temporal lobes also presented some morphometric differences even if they are not significant. Though not significant, the temporal lobes also presented some morphometric differences. Finally, differences in volume were also found in parts of the corpus callosum considered to carry fibers connecting the temporal and occipital lobes of both hemispheres.

Modern life is highly dependent on high-acuity vision, and this chapter emphasizes the mechanisms and pathways that support high-acuity or form vision. Because the most common visual impairment is refractive error, the refractive power of the cornea and lens is described at some length. The processes of emmetropization, accommodation, and far viewing are considered. The participation of the outer retina in phototransduction and the visual cycle are detailed, and relevant diseases, including retinitis pigmentosa and age-related macular degeneration, are introduced. The neural processes that transform different wavelengths of light into color perception and common forms of color blindness are explained. Visual processing within cortex, including processing through the dorsal and visual streams, are presented. The process through which babies learn to interpret the firing in their brains as representing visual objects and the importance of the initial years of life to this process are described.

The seventh chapter shows how the empirical premise can accommodate evidence for the dual visual systems in cognitive neuroscience. The main claim of this chapter is that the crucial difference between the two cortical streams is in their spatiotemporal processing, rather than their functional output: the dorsal stream processes peripheral retinal input with a high temporal resolution, and the ventral stream specializes in foveal input with less temporal resolution.

Event-based cameras have attracted increasing attention due to their advantages of biologically inspired paradigm and low power consumption. Since event-based cameras record the visual input as asynchronous discrete events, they are inherently suitable to cooperate with the spiking neural network (SNN). Existing works of SNNs for processing events mainly focus on the task of object recognition. However, events from the event-based camera are triggered by dynamic changes, which makes it an ideal choice to capture actions in the visual scene. Inspired by the dorsal stream in visual cortex, we propose a hierarchical SNN architecture for event-based action recognition using motion information. Motion features are extracted and utilized from events to local and finally to global perception for action recognition. To the best of the authors’ knowledge, it is the first attempt of SNN to apply motion information to event-based action recognition. We evaluate our proposed SNN on three event-based action recognition datasets, including our newly published DailyAction-DVS dataset comprising 12 actions collected under diverse recording conditions. Extensive experimental results show the effectiveness of motion information and our proposed SNN architecture for event-based action recognition.

Introduction: Cannabis is widely popular recreational drug of choice in the US. The drug is known to alter the subjective experience of time. However, its effects on time estimation at a brain level are still largely unexplored. Our goal was to investigate acute effects of cannabis on an fMRI time estimation task by evaluating brain activation differences between cannabis and placebo conditions. We hypothesized that participants’ time estimation accuracy and corresponding BOLD response would be altered during the cannabis condition in a dose-related manner, compared to placebo. Methods: In this placebo-controlled, double-blind randomized trial, a total of N=44 participants had 3 dose visits, at each of which they received either high-dose cannabis (0.5 gm of ~12.5% THC flower), low dose cannabis (0.5 gm of ~5.7% flower) or 0.5 gm placebo, using paced inhalation from a volcano via vaporizer. Drug material was supplied by NIDA/RTI. For the current study we analyzed fMRI data from the first of placebo and high dose fMRI sessions throughout each dosing day in which participants performed a time estimation task. Participants were asked to respond with a mouse click as to which box of two boxes displayed for different intervals was displayed on the screen longer. Both sub-second and supra-second temporal intervals were tested, with a range of easy to hard discriminations. We used the Human Connectome Project processing pipeline to prepare fMRI data for GLM modeling of activation using the FSL FEAT toolbox. This model estimated the unique effect sub-second (short) and supra-second (long) interval discrimination, their average effect, and their difference. From these contrasts, the mean activation amplitudes within 387 brain parcels from the Human Connectome cortical atlas were extracted. Robust statistics in R software estimated a paired t test equivalent using the bootdpci function to assess the difference between placebo and the high dose drug conditions for each contrast. Results: Only premotor cortex survived False Discovery Rate corrections for searching all 387 parcels across the entire brain for the average of short and long temporal estimation conditions. Numerous other brain regions differed between placebo and high doses at p<.05 uncorrected for various task contrasts: Short duration stimuli: Premotor cortex, posterior cingulate cortex, medial temporal cortex, visual area, somatosensory cortex, anterior cingulate and medial prefrontal cortex, paracentral and mid-cingular cortex, inferior frontal cortex. Long duration stimuli: Premotor cortex, visual areas, somatosensory motor cortex, paracentral and mid- cingulate cortex, the tempo-parieto-occipital junction, dorsolateral-prefrontal cortex, posterior opercular cortex, medial temporal cortex, posterior cingulate cortex, orbito-frontal cortex. Average of short and long duration stimuli: Premotor cortex, somatosensory and motor cortex, posterior cingulate cortex, visual are, medial temporal cortex, paracentral and midcingulate cortex, anterior cingulate and medial prefrontal cortex, inferior frontal cortex, tempo-parieto-occipital junction, premotor cortex, somatosensory motor cortex, posterior cingulate cortex, medial temporal cortex, orbital and polar frontal cortex, hippocampus. Difference of short and long duration stimuli: Anterior cingulate and medial prefrontal cortex, ventral stream visual cortex, dorsal stream visual cortex, early visual cortex. Conclusions: The current study elicited multiple brain activation differences for the initial, acute high-dose cannabis vs. placebo condition, but only premotor cortex region survived as significant following multiple comparison correction for short and long duration stimuli contrast. A post hoc power analysis showed that adding 10 additional subjects to this sample would achieve significance with multiple comparison correction for medium effect sizes at alpha=0.05. Future studies on a larger sample can help identify such significant activation differences, and examining all doses and tasks would elucidate unfolding of effects longitudinally post-dose, and dose-dependence of effects.

Abstract: The article presents the results of a psychophysiological examination of drivers of passenger and export traffic, working in the day and night shifts, respectively. The dynamics of performing psychophysiological tests (changes in the reaction rate, the number of errors, perception of time intervals, etc.) after day and night shifts was revealed, and differences in the subjective perception of the specifics of work in the daytime and at night were also noted. Working the night shift requires the driver to mobilize psychophysiological resources aimed at maintaining active wakefulness and fighting monotony. Day trips are perceived to be more stressful due to more input and traffic. Target: The study of the functional state dynamics of train drivers working without an assistant during day and night trips with an increase in the duration of working hours up to 8 hours in passenger traffic and up to 12 - in export traffic. Methods: 1. Express test of the functional state; 2. «Sense of time» test; 3. Stress resistance test; 4. Survey «Well-being. Activity, mood (SAN)»; 5. Survey «Diagnostics of states of reduced performance (DORS)». Results: The dynamics of the speed and stability of the visual-motor reaction, the accuracy of the perception of time intervals, as well as the subjective perception of the features of day and night shifts by train drivers themselves, makes it possible to distinguish differences in the specifics of shift work: in the daytime it is distinguished by greater intensity, tension, which is reflected in the number of erroneous actions during testing after a day's ride on the simulator, and in the subjective experience of stress noted by the drivers. The need to work at night requires considerable efforts from train drivers to mobilize, which is manifested during a psychophysiological examination before the night shift, however, forced wakefulness during night work leads to a state of monotony among train drivers.

In modern workplaces with rapidly changing skill requirements, suitable training and learning environments play a key role for companies to remain competitive, effective and ensure job satisfaction. To provide an immersive, interactive, and engaging learning experience, Virtual Reality (VR) has emerged as a revolutionary technology. Especially when erroneous behaviour is associated with severe consequences or great resources, VR offers the opportunity to explore actions and visualize consequences in safely and at affordable costs. In addition, it provides an easy way to personalize educational content, learning speed, and/or format to the individual to guarantee a good fit with skills and needs. This is decisive, since insufficient or excessive workload during training sessions results in demotivation and reduced performance. In the latter case, persistent professional exhaustion, pressure to succeed and stress can lead to long-term psychological consequences for employees. Besides skill and ability, current physical conditions (e.g., illness or fatigue) and psychological states (e.g., motivation) also affect the learning performance. To identify and monitor individual mental states, Brain-Computer Interfaces (BCI) measuring neurophysiological activation patterns, e.g., with an electroencephalography (EEG), or functional near-infrared spectroscopy (fNIRS) can be integrated in a VR-learning environment. Recently, fNIRS, a mobile optical brain imaging technique, has become popular for real-world applications due to its good usability, portability, and ease of use. For the reliable online decoding of mental states, informative neuronal patterns, suitable methods for pre-processing and artefact removal, as well as efficient machine learning algorithms for the classification need to be explored. We, therefore, investigated and decoded different working memory states in a free moving fNIRS experiment presented in VR. different working memory states in a free moving fNIRS VR experiment and the possibility of decoding these states properly. 11 volunteers (four female, right-handed, mean age of 23.73, SD = 1.42, range = 21−26 years) participated in the study. The experimental task was a colour-based visuo-spatial n-back paradigm adapted from Lühmann and colleagues (2019) with a low (1-back) and high working memory load condition (3-back) and a 0-back condition as active baseline. Brain activity was recorded using the mobile NIRx NIRSport2. To capture brain activation patterns associated with working memory load, optode montage was designed to optimally cover the prefrontal cortex (PFC; in particular, dorso- and ventrolateral parts of the PFC) with some lateral restriction by the VR head-mounted display (HMD). fNIRS signals were processed using the python-toolbox mne and mne-nirs. For the decoding of working memory load, we extracted statistical features, that are peak, minimum, average, slope, peak-to-peak, and time-to-peak, from epochs of oxygenated (HbO) and deoxygenated (HbR) hemoglobin concentration per channel. A Linear Discriminant Analysis (LDA), Support Vector Machine (SVM) and Gradient Boosting classifier (XGBoost) were explored and compared to a Dummy classifier (empirical chance level). We also investigated which cortical regions contributed to the decoding when choosing single features and which feature combination was suggested to optimize performance. With this study, we aim to provide empirically supported decision recommendations to reach the next step towards future online decoding pipelines in real-world VR-based learning applications.