Reduced 2D form coherence and 3D structure from motion sensitivity in developmental dyscalculia

Developmental dyscalculia (DD) is a specific learning disability affecting the development of numerical and arithmetical skills. The origin of DD is typically attributed to the suboptimal functioning of key regions within the dorsal visual stream (parietal cortex) which support numerical cognition. While DD individuals are often impaired in visual numerosity perception, the extent to which they also show a wider range of visual dysfunctions is poorly documented. In the current study we measured sensitivity to global motion (translational and flow), 2D static form (Glass patterns) and 3D structure from motion in adults with DD and control subjects. While sensitivity to global motion was comparable across groups, thresholds for static form and structure from motion were higher in the DD compared to the control group, irrespective of associated reading impairments. Glass pattern sensitivity predicted numerical abilities, and this relation could not be explained by recently reported differences in visual crowding. Since global form sensitivity has often been considered an index of ventral stream function, our findings could indicate a cortical dysfunction extending beyond the dorsal visual stream. Alternatively, they would fit with a role of parietal cortex in form perception under challenging conditions requiring multiple element integration

The neural coding of properties shared by faces, bodies and objects

Previous studies have identified relatively separated regions of the brain that respond strongly when participants view images of either faces, bodies or objects. The aim of this thesis was to investigate how and where in the brain shared properties of faces, bodies and objects are processed. We selected three properties that are shared by faces and bodies, shared categories (sex and weight), shared identity and shared orientation (i.e. facing direction). We also investigated one property shared by faces and objects, the tendency to process a face or object as a whole rather than by its parts, which is known as holistic processing. We hypothesized that these shared properties might be encoded separately for faces, bodies and objects in the previously defined domain-specific regions, or alternatively that they might be encoded in an overlapping or shared code in those or other regions. In all of studies in this thesis, we used fMRI to record the brain activity of participants viewing images of faces and bodies or objects that showed differences in the shared properties of interest. We then investigated the neural responses these stimuli elicited in a variety of specifically localized brain regions responsive to faces, bodies or objects, as well as across the whole-brain. Our results showed evidence for a mix of overlapping coding, shared coding and domain-specific coding, depending on the particular property and the level of abstraction of its neural coding. We found we could decode face and body categories, identities and orientations from both face- and body-responsive regions showing that these properties are encoded in overlapping brain regions. We also found that non-domain specific brain regions are involved in holistic face processing. We identified shared coding of orientation and weight in the occipital cortex and shared coding of identity in the early visual cortex, right inferior occipital cortex, right parahippocampal cortex and right superior parietal cortex, demonstrating that a variety of brain regions combine face and body information into a common code. In contrast to these findings, we found evidence that high-level visual transformations may be predominantly processed in domain-specific regions, as we could most consistently decode body categories across image-size and body identity across viewpoint from body-responsive regions. In conclusion, this thesis furthers our understanding of the neural coding of face, body and object properties and gives new insights into the functional organisation of occipitotemporal cortex

Dysfunctions of visual and auditory Gestalt perception (amusia) after stroke : Behavioral correlates and functional magnetic resonance imaging

Music is a special and unique part of human nature. Not only actively playing (making music in a group or alone) but also passive listening to music involves a richness of processes to make music the ideal tool to investigate how the human brain works. Acquired amusia denotes the impaired perception of melodies, rhythms, and the associated disability to enjoy music which can occur after a stroke. Many amusia patients also show deficits in visual perception, language, memory, and attention. Hence, the question arises whether amusia actually describes an independent clinical picture or is better described by a general perceptual deficit for auditory, as well as visual, and speech-related material. Additionally, the question in what way impaired abilities in attention and working memory influence the performance in the music perception task remains to be investigated. Behavioral investigations, lesion analysis, and functional magnetic resonance imaging were performed to assess the anatomical and functional correlates of these deficits. A better and more detailed understanding of amusia and connected cognitive deficits is not only relevant in terms of fundamental neuroscience but also from a clinical point of view: symptoms of amusia are rare, mostly undiscovered, and the underlying mechanisms are hitherto insufficiently understood

The role of the parietal cortex in salience-based selection using a cognitive neuropsychological approach

It has been known that the parietal cortex is important for directing attention in order to fulfil search task goals, although how exactly this is done is unclear. Saliency has been identified as important in parietal selection of targets and suppression of distractors. This thesis attempted to explore the factors underlying salience-based selection in the parietal cortex using a cognitive neuropsychological approach. Chapter 1 explored the literature underlying saliency and the parietal cortex. Chapter 2 addressed the question of salience-based selection in a global-local task using a voxel-based morphometric approach in a wide range of patients, finding parietal and occipital regions as important regions for congruency interference and suppressing salient distractors. Chapter 3 inhibited the right precuneus using repetitive transcranial magnetic stimulation in neurotypical adults on the same task finding reduced congruency interference. Chapter 4 revealed the importance of saliency in mediating level selection in simultanagnosia. Chapters 5 and 6 examined in a bilateral parietal patient using spatial and non-spatial paradigms the importance of stimulus relevance as a means of guiding salience-based selection. The thesis concluded in Chapter 7 that the parietal cortex is important for salience-based selection and suppression mediated by the relevance of the stimulus being made salient