The role of the left ventral occipitotemporal cortex in speech processing—The influence of visual deprivation

The role of the left ventral occipitotemporal cortex (vOT) in reading is well-established in both sighted and blind readers. Its role in speech processing remains only partially understood. Here, we test the involvement of the left vOT in phonological processing of spoken language in the blind (N = 50, age: 6.76–60.32) and in the sighted (N = 54, age: 6.79–59.83) by means of whole-brain and region-of-interest (including individually identified) fMRI analyses. We confirm that the left vOT is sensitive to phonological processing (shows greater involvement in rhyming compared to control spoken language task) in both blind and sighted participants. However, in the sighted, the activation was observed only during the rhyming task and in the speech-specific region of the left vOT, pointing to task and modality specificity. In contrast, in the blind group, the left vOT was active during speech processing irrespective of task and in both speech and reading-specific vOT regions. Only in the blind, the left vOT presented a higher degree of sensitivity to phonological processing than other language nodes in the left inferior frontal and superior temporal cortex. Our results suggest a changed development of the left vOT sensitivity to spoken language, resulting from visual deprivation

Preservation and plasticity in the neural basis of numerical thinking in blindness

Numerical reasoning pervades modern human culture and depends on a fronto-parietal network, a key node of which is the intraparietal sulcus (IPS). In this dissertation I investigate how visual experience shapes the cognitive and neural basis of numerical thinking by studying numerical cognition in congenitally blind individuals. In Chapter 2, I ask how the cognitive basis of numerical thinking is shaped by visual experience. I test whether the precision of approximate number representations develops normally in the absence of vision and test whether the relationship between numerical approximation and math abilities is preserved in congenital blindness. In Chapter 3, I ask how the neural basis of symbolic number reasoning is modified by visual experience by studying neural responses to symbolic math in congenitally blind individuals. This initial investigation revealed that the fronto-parietal number system is preserved in blindness but that some “visual” cortices are recruited for symbolic number processing in blindness. The following chapters unpack these two patterns preservation and plasticity. In Chapter 4, I use resting-state data to ask whether functional connectivity with higher-cognitive networks is a potential mechanism by which “visual” cortices are reorganized in blindness. In Chapter 5, I work with individuals who became blind as adults to determine whether visual cortex plasticity for numerical functions is possible in the adult cortex or whether it is restricted to sensitive periods in development. In Chapter 6, I investigated whether the IPS and newly identified number-responsive “visual” area of congenitally blind individuals possess population codes that distinguish between different quantities. I find that the behavioral signatures of numerical reasoning are indistinguishable across congenitally blind and sighted groups and that the fronto-parietal number network, in particular the IPS, is preserved in the absence of vision. A dorsal occipital region showed the same functional profile as the IPS number system in congenitally blind individuals. Number-related plasticity was restricted to a sensitive period in development as it was not observed in adult-onset blind individuals. Furthermore, in congenital blindness, sub-specialization of the “visual” cortex for math and language processing followed the functional connectivity patterns of “visual” cortex

Brain connectivity and sensory stimulation in patients with disorders of consciousness

This thesis explores brain connectivity and sensory stimulation in patients with disorders of consciousness (DOC). These are serious conditions where massive brain damage can lead to a dissociation between arousal and awareness (e.g., UWS and MCS). Part I explores brain connectivity. We highlight that brain function and structure are intimately related to each other, and to consciousness. The decrease in brain function can be used to distinguish between the clinically indicated states of consciousness. Part II evaluates passive sensory stimulations. Preferred stimuli may have the power to momentarily enhance brain function, and behavioral responses

Visuospatial coding as ubiquitous scaffolding for human cognition

For more than 100 years we have known that the visual field is mapped onto the surface of visual cortex, imposing an inherently spatial reference frame on visual information processing. Recent studies highlight visuospatial coding not only throughout visual cortex, but also brain areas not typically considered visual. Such widespread access to visuospatial coding raises important questions about its role in wider cognitive functioning. Here, we synthesise these recent developments and propose that visuospatial coding scaffolds human cognition by providing a reference frame through which neural computations interface with environmental statistics and task demands via perception–action loops

Coming of age: a review of embodiment and the neuroscience of semantics

Over the last decade, there has been an increasing body of work that explores whether sensory and motor information is a necessary part of semantic representation and processing. This is the embodiment hypothesis. This paper presents a theoretical review of this work that is intended to be useful for researchers in the neurosciences and neuropsychology. Beginning with a historical perspective, relevant theories are placed on a continuum from strongly embodied to completely unembodied representations. Predictions are derived and neuroscientific and neuropsychological evidence that could support different theories is reviewed; finally, criticisms of embodiment are discussed. We conclude that strongly embodied and completely disembodied theories are not supported, and that the remaining theories agree that semantic representation involves some form of Convergence Zones (Damasio, 1989) and the activation of modal content. For the future, research must carefully define the boundaries of semantic processing and tackle the representation of abstract entities

A Neurobiologically Constrained Model

Understanding the meaning of words and its relationship with the outside world involves higher cognitive processes unique of the human brain. Despite many decades of research on the neural substrates of semantic processing, a consensus about the functions and components of the semantic system has not been reached among cognitive neuroscientists. This issue is mainly influenced by two sets of neurocognitive empirical findings that have shown (i) the existence of several regions acting as ’semantic hubs’, where the meaning of all types of words is processed and (ii) the presence of other cortical regions specialised for the processing of specific semantic word categories, such as animals, tools, or actions. Further evidence on semantic meaning processing comes from neuroimaging and transcranial magnetic stimulation studies in visually deprived population that acquires semantic knowledge through non-sensory modalities. These studies have documented massive neural changes in the visual system that is in turn recruited for linguistic and semantic processing. On this basis, this dissertation investigates the neurobiological mechanism that enables humans to acquire, store and processes linguistics meaning by means of a neurobiologically constrained neural network and offers an answer to the following hotly debated questions: Why both semantic hubs and modality-specific regions are involved in semantic meaning processing in the brain? Which biological principles are critical for the emergence of semantics at the microstructural neural level and how is the semantic system implemented under deprived conditions, in particular in congenitally blind people? First, a neural network model closely replicating the anatomical and physiological features of the human cortex was designed. At the micro level, the network was composed of 15,000 artificial neurons; at the large-scale level, there were 12 areas representing the frontal, temporal, and occipital lobes relevant for linguistic and semantic processing. The connectivity structure linking the different cortical areas was purely based on neuroanatomical evidence. Two models were used, each simulating the same set of cortical regions but at different level of details: one adopted a simple connectivity structure with a mean-field approach (i.e. graded-response neurons), and the other used a fully connected model with adaptation-based spiking cells. Second, the networks were used to simulate the process of learning semantic relationships between word-forms, specific object perceptions, and motor movements of the own body in deprived and undeprived visual condition. As a result of Hebbian correlated learning, distributed word-related cell assembly circuits spontaneously emerged across the different cortical semantic areas exhibiting different topographical distribution. Third, the network was reactivated with the learned auditory patterns (simulating word recognition processes) to investigate the temporal dynamics of cortical semantic activation and compare them with real brain responses. In summary, the findings of the present work demonstrate that meaningful linguistic units are represented in the brain in the form of cell assemblies that are distributed over both semantic hubs and category-specific regions spontaneously emerged through the mutual interaction of a single set of biological mechanisms acting within specific neuroanatomical structures. These biological principles acting together also offer an explanation of the mechanisms underlying massive neural changes in the visual cortex for language processing caused by blindness. The present work is a first step in better understanding the building blocks of language and semantic processing in sighted and blind populations by translating biological principles that govern human cognition into precise mathematical neural networks of the human brain.Um die Bedeutung von Wörtern und ihre Beziehung zur Außenwelt zu verstehen, müssen die kognitiven Prozesse betrachtet werden, die einzigartig für das menschliche Gehirn sind. Trotz jahrzehntelanger Forschungen an den neuronalen Substraten der semantischen Verarbeitung im menschlichen Gehirn wurde bisher kein Konsens über die Funktionen und Komponenten des semantischen Systems in den kognitiven Neurowissenschaftlern erreicht. Dieses Problem gründet darin, dass neurokognitive empirische Studien zumeist zu zwei Endergebnissen kamen: (i) der Existenz von mehrere Regionen, die als ‘semantische Hubs’ fungieren, in denen die Bedeutung aller Wortarten verarbeitet wird, und (ii) dem Vorhandensein weiterer kortikaler Regionen, die auf die Verarbeitung spezifischer semantischer Kategorien wie Tiere, Werkzeuge oder Aktionswörtern spezialisiert sind. Ein weiterer Beweis für die Verarbeitung semantischer Bedeutungen lässt sich aus Bildgebungsstudien und Studien mit transkranialer Magnetstimulation an visuell benachteiligten Probanden entnehmen, die die linguistische Bedeutung nicht durch sensorische Modalitäten erwerben. Diese Studien konnten massive neuronale Veränderungen im visuellen System dokumentieren, die wiederum für die sprachliche und semantische Verarbeitung verwendet werden. Die vorliegende Dissertation untersucht mittels eines biologischen neuronalen Netzwerkes jene kognitiven Prozesse, die es Menschen ermöglichen, linguistische Bedeutungen in der täglichen Kommunikation zu erfassen, zu speichern und zu verarbeiten. Sie schlägt Antworten auf die folgenden neurowissenschaftlich heiß diskutierten Fragen vor: Warum sind sowohl semantische Hubs als auch modalitätsspezifische Regionen relevant für die sprachliche und semantische Informationsverarbeitung im Gehirn? Welche biologischen Prinzipien sind von entscheidender Bedeutung für die Entstehung von Semantik auf mikrostruktureller neuronaler Ebene? Und Wie ist das semantische System unter benachteiligten Bedingungen repräsentiert? Zunächst wurde ein neuronales Netzwerkmodell implementiert, das die anatomischen und physiologischen Merkmale des menschlichen Kortex präzise widerspiegelt. Auf der Mikroebene besteht das Netzwerkmodel aus 15.000 künstlichen Neuronen, auf der Großebene aus 12 Arealen der Frontal-, Temporal- und Okzipitallappen, die für die sprachliche und semantische Verarbeitung relevant sind. Die Verbindungsstruktur zwischen den verschiedenen kortikalen Arealen wurde rein auf Grundlage von neuroanatomischen Befunden implementiert. Zwei Modelle wurden verwendet, die jeweils die gleichen kortikalen Regionen simulierten, allerdings in verschiedenen Varianten: Das erste Modell ging von einer einfachen Konnektivitätsstruktur mit einem Mean-field Ansatz (graded-response neurons) aus, während das zweite einen vollständig verbundenen Aufbau mit adaptionsbasierten Spiking-Zellen (Aktionspotential) verwendete. Anschließend dienten die neuronalen Netzwerke dazu, den Lernprozess der semantischen Verlinkung zwischen Wortformen, bestimmten Objektwahrnehmungen und motorischen Bewegungen des eigenen Körpers zu simulieren, sowohl in gesundem als auch in benachteiligtem Sehzustand. Als Ergebnis des Hebbschen Korrelationslernens traten spontan verteilte Neuronenverbindungen (cell assemblies) in den verschiedenen kortikalen semantischen Bereichen auf, die unterschiedliche topografische Verteilungen zeigten. Zuletzt wurde das Netzwerkmodell mit den erlernten auditorischen Mustern reaktiviert (Worterkennungsprozesse), um die zeitliche Dynamik kortikaler semantischer Aktivierung zu untersuchen und sie mit realen Gehirnantworten zu vergleichen. Die vorliegende Arbeit kam zu folgenden Ergebnissen: Die neuronale Repräsentation linguistischer Bedeutung wird im Gehirn in Form von cell assemblies dargestellt, welche über semantische Hubs und modalitätsspezifische Regionen verteilt sind. Diese entstehen spontan durch die Interaktion einer Reihe von biologischen Mechanismen, die innerhalb spezifischer neuroanatomischer Strukturen wirken. Das Zusammenwirken dieser biologischen Prinzipien bietet zusätzlich eine Erklärung für jene Faktoren, die für die massiven neuronalen Veränderungen in der sprachlichen und semantischen Netzwerke bei Blindheit verantwortlich sind. Die in dieser Dissertation dokumentierten Studien sind ein erster Schritt in Richtung eines besseren Verständnisses der sprachlichen und semantischen Informationsverarbeitung bei sehenden und blinden Menschen, basierend auf einer Übersetzung der biologischen Prinzipien der menschlichen Kognition in präzise mathematische neuronale Netzwerke des menschlichen Gehirns

Neural and socio-cognitive sequelae of congenital visual impairment during midchildhood

Previous studies identified cognitive difficulties in individuals with congenital visual impairment that significantly impacted on wellbeing and educational attainment. However, factors leading to adverse outcome remained unclear. The current study aimed to identify associations and mechanisms of specific cognitive deficits associated with visual impairment from a neurodevelopmental perspective. Based on recent theoretical advances (Johnson, 2011), it was assumed that visual impairment leads to differences in cognition by influencing experience-driven brain maturational processes, which support the integration between cortical areas to support cognitive processes. In order to explore this hypothesis, children with visual impairment due to disorders that were thought to only affect peripheral sensory parts of the visual system were assessed on neuropsychological instruments covering a range of functional domains. Further, structural and functional neurophysiological methods were employed to establish the impact of visual impairment on brain organisation. The results of the present work confirm earlier reports of specific deficits in spatial memory, social understanding, and aspects of executive function, despite typical performance in other domains. In addition, the current study is the first study to indicate dosage-dependence with some aspects of social communication being even impaired in children with only mild to moderate visual impairment, while aspects of executive function and spatial memory were only found to be deficient in children with more severe forms of visual impairment. Further, neurophysiological investigations indicated differences in structural and functional brain organisation in children with VI that related to differences in behavioural performance. In general, the results of the present study suggest that visual sensory impairment impacts on brain and cognitive development with important implications for education and clinical treatment of children with visual impairment

Towards a model of human body perception

Item does not contain fulltextFrom just a glimpse of another person, we make inferences about their current states and longstanding traits. These inferences are normally spontaneous and effortless, yet they are crucial in shaping our impressions and behaviours towards other people. What are the perceptual operations involved in the rapid extraction of socially relevant information? To answer this question, over the last decade the visual and cognitive neuroscience of social stimuli has received new inputs through emerging proposals of social vision approaches. Perhaps by function of these contributions, researchers have reached a certain degree of consensus over a standard model of face perception. This thesis aims to extend social vision approaches to the case of human body perception. In doing so, it establishes the building blocks for a perceptual model of the human body which integrates the extraction of socially relevant information from the appearance of the body. Using visual tasks, the data show that perceptual representations of the human body are sensitive to socially relevant information (e.g. sex, weight, emotional expression). Specifically, in the first empirical chapter I dissect the perceptual representations of body sex. Using a visual search paradigm, I demonstrate a differential and asymmetrical representation of sex from human body shape. In the second empirical chapter, using the Garner selective attention task, I show that the dimension of body sex is independent from the information of emotional body postures. Finally, in the third empirical chapter, I provide evidence that category selective visual brain regions, including the body selective region EBA, are directly involved in forming perceptual expectations towards incoming visual stimuli. Socially relevant information of the body might shape visual representations of the body by acting as a set of expectancies available to the observer during perceptual operations. In the general discussion I address how the findings of the empirical chapters inform us about the perceptual encoding of human body shape. Further, I propose how these results provide the initial steps for a unified social vision model of human body perception. Finally, I advance the hypothesis that rapid social categorisation during perception is explained by mechanisms generally affecting the perceptual analysis of objects under naturalistic conditions (e.g. expectations-expertise) operating within the social domain.Bangor University, 17 februari 2020Promotor : Downing, P.E. Co-promotor : Koldewyn, K.182 p