Learned optical flow for intra-operative tracking of the retinal fundus

Purpose: Sustained delivery of regenerative retinal therapies by robotic systems requires intra-operative tracking of the retinal fundus. We propose a supervised deep convolutional neural network to densely predict semantic segmentation and optical flow of the retina as mutually supportive tasks, implicitly inpainting retinal flow information missing due to occlusion by surgical tools. / Methods: As manual annotation of optical flow is infeasible, we propose a flexible algorithm for generation of large synthetic training datasets on the basis of given intra-operative retinal images. We evaluate optical flow estimation by tracking a grid and sparsely annotated ground truth points on a benchmark of challenging real intra-operative clips obtained from an extensive internally acquired dataset encompassing representative vitreoretinal surgical cases. / Results: The U-Net-based network trained on the synthetic dataset is shown to generalise well to the benchmark of real surgical videos. When used to track retinal points of interest, our flow estimation outperforms variational baseline methods on clips containing tool motions which occlude the points of interest, as is routinely observed in intra-operatively recorded surgery videos. / Conclusions: The results indicate that complex synthetic training datasets can be used to specifically guide optical flow estimation. Our proposed algorithm therefore lays the foundation for a robust system which can assist with intra-operative tracking of moving surgical targets even when occluded

Recognizing Speech in a Novel Accent: The Motor Theory of Speech Perception Reframed

The motor theory of speech perception holds that we perceive the speech of another in terms of a motor representation of that speech. However, when we have learned to recognize a foreign accent, it seems plausible that recognition of a word rarely involves reconstruction of the speech gestures of the speaker rather than the listener. To better assess the motor theory and this observation, we proceed in three stages. Part 1 places the motor theory of speech perception in a larger framework based on our earlier models of the adaptive formation of mirror neurons for grasping, and for viewing extensions of that mirror system as part of a larger system for neuro-linguistic processing, augmented by the present consideration of recognizing speech in a novel accent. Part 2 then offers a novel computational model of how a listener comes to understand the speech of someone speaking the listener's native language with a foreign accent. The core tenet of the model is that the listener uses hypotheses about the word the speaker is currently uttering to update probabilities linking the sound produced by the speaker to phonemes in the native language repertoire of the listener. This, on average, improves the recognition of later words. This model is neutral regarding the nature of the representations it uses (motor vs. auditory). It serve as a reference point for the discussion in Part 3, which proposes a dual-stream neuro-linguistic architecture to revisits claims for and against the motor theory of speech perception and the relevance of mirror neurons, and extracts some implications for the reframing of the motor theory

The get big fast as a business model in e-commerce : a case study of Zalando

The purpose of this thesis is to identify the properties of the internet that help e-commerce companies to growth so much and so fast, along with the analysis of the Get Big Fast strategy. Such strategy exploits online business activities based on first mover advantage, allowing incumbents to preempt competition by gaining market share as fast as possible and generate positive feedbacks. This qualitative research is a case-study of Zalando, an online fashion retailer. Though initially specialized in footwear, the firm quickly broadened its product portfolio, expanded into new markets and acquired millions of clients, becoming the Europe’s market leader. Hence, this study investigates to what extent Zalando has followed the Get Big Fast principles, based on data provenient from five interviews and multiple secondary sources. The findings indicate that certain properties of the internet stimulate the scalability of business operations, such as: 1) Mediating Technology 2) Information Density 3) Universal Standards 4) Distribution Channel 5) Infinite Virtual Capacity and 6) Global Reach. Moreover, it was found that Zalando has actually pursued the Get Big Fast strategy by being an early mover in the market, applying three out of four common tactics to gain market share (capacity expansion, heavy advertising and formation of strategic alliances), following product and market development strategies and generating four positive feedbacks (economies of scale, learning effects, network effects and accumulation of complementary assets). Nevertheless, some limitations exist, including an extensive scope of research, limited amount of interviews conducted via Skype and a generalization problem.O propósito desta tese é indentificar as propriedades da Internet que ajudam as empresas de comércio electrónico a crescer tanto e tão rápido, juntamente com a análise da estratégia Get Big Fast. Esta estratégia explora a actividade económica online baseada em first mover advantage, permindo aos incumbentes antecipar os seus rivais através da rápida conquista de quota de mercado e da produção de feedbacks positivos. Este estudo qualitativo é um caso de estudo sobre a Zalando, uma loja virtual de moda. Apesar de ser inicialmente especializada em calçado, a empresa alargou rapidamente o seu portofolio de produtos, expandiu-se para novos mercados e adquiriu milhões de clientes, tornando-se no líder de mercado Europeu. Portanto, esta tese investiga em que medida a Zalando segiu os princípios Get Big Fast, de acordo com informação recolhida em cinco entrevistas e múltiplas fontes secundárias. Os resultados indicam que certas propriedades da Internet estimulam a expansibilidade do comércio online, tais como: 1) Tecnologia Mediadora 2) Densidade de Informação 3) Normas Universais 4) Canal de Distribuição 5) Capacidade Virtual Infinita 6) Alcance Global. Além disso, verificou-se que a Zalando seguiu efectivamente uma estratégia Get Big Fast por ser pioneira no mercado, aplicar três de quatro tácticas comuns destinadas à conquista de quota de mercado (expansão de capacidade, forte investimento publicitário e formação de alianças estratégicas), seguir estratégias de desenvolvimento de produtos e mercados e gerar quatro feedbacks positivos (economias de escala, efeitos de aprendizagem, efeitos de rede e acumulação de activos complementares). Contudo, existem algumas limitações, tais como o extenso âmbito de investigação, o número limitado de entrevistas realizadas por Skype e um problema de generelização

The role of chromatic texture and 3D shape in colour discrimination, memory colour, and colour constancy of natural objects

The primary goal of this work was to investigate colour perception in a natural environment and to contribute to the understanding of how cues to familiar object identity influence colour appearance. A large number of studies on colour appearance employ 2D uniformly coloured patches, discarding perceptual cues such as binocular disparity, 3D luminance shading, mutual reflection, and glossy highlights are integral part of a natural scene. Moreover, natural objects possess specific cues that help our recognition (shape, surface texture or colour distribution). The aim of the first main experiment presented in this thesis was to understand the effect of shape on (1) memory colour under constant and varying illumination and on (2) colour constancy for uniformly coloured stimuli. The results demonstrated the existence of a range of memory colours associated with a familiar object, the size of which was strongly object-shape-dependent. For all objects, memory retrieval was significantly faster for object-diagnostic shape relative to generic shapes. Based on two successive controls, the author suggests that shape cues to the object identity affect the range of memory colour proportionally to the original object chromatic distribution. The second experiment examined the subject’s accuracy and precision in adjusting a stimulus colour to its typical appearance. Independently on the illuminant, results showed that memory colour accuracy and precision were enhanced by the presence of chromatic textures, diagnostic shapes, or 3D configurations with a strong interaction between diagnosticity and dimensionality of the shape. Hence, more cues to the object identity and more natural stimuli facilitate the observers in accessing their colour information from memory. A direct relationship was demonstrated between chromatic surface representation, object’s physical properties, and identificability and dimensionality of shape on memory colour accuracy, suggesting high-level mechanisms. Chromatic textures facilitated colour constancy. The third and fourth experiments tested the subject’s ability to discriminate between two chromatic stimuli in a simultaneous and successive 2AFC task, respectively. Simultaneous discrimination threshold performances for polychromatic surfaces were only due to low-level mechanism of the stimulus, whereas in the successive discrimination, i.e. when memory is involved, high-level mechanisms were established. The effect of shape was strongly task- dependent and was modulate by the object memory colour. These findings together with the strong interaction between chromatic cues and shape cues to the object identity lead to the conclusion that high level mechanisms linked to object recognition facilitated both tasks. Hence, the current thesis presents new findings on memory colour and colour constancy presented in a natural context and demonstrates the effect of high-level mechanisms in chromatic discrimination as a function of cues to the object identity such as shape and texture. This work contributes to a deeper understanding of colour perception and object recognition in the natural world.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Form and function: assessing the impact of mental representation on behaviour using computational models

This thesis presents three studies examining the methods used by human learners to construct mental representations to reflect external data patterns, and the impact the form of these representations have on subsequent behaviour. This involves three varied tasks in which representations are built and updated from experience: stereotype change, numerical estimation and learning consolidation. Each of these studies uses computational models of these processes to offer potential descriptions of the mechanisms used to construct our representations, and assesses the accuracy of these descriptions using both qualitative and quantitative comparisons with human behaviour. Such contrasts reveal the importance of the form of our mental representations on related actions: stereotypical beliefs are coloured by the organisation of group members, numerical expectations are dependent on the assumed format of numerical information, and stimulus choices are influenced by connections forged through experience. This then provides insight into the mechanisms used by human learners in these tasks, and the specific impacts of such mechanisms on related behaviour. We do however also note questions raised by the use of such methods on the accuracy of what may be highly-complex systems in describing human behaviour, and the algorithms that may be used to implement such systems in real life

How touch and hearing influence visual processing in sensory substitution, synaesthesia and cross-modal correspondences

Sensory substitution devices (SSDs) systematically turn visual dimensions into patterns of tactile or auditory stimulation. After training, a user of these devices learns to translate these audio or tactile sensations back into a mental visual picture. Most previous SSDs translate greyscale images using intuitive cross-sensory mappings to help users learn the devices. However more recent SSDs have started to incorporate additional colour dimensions such as saturation and hue. Chapter two examines how previous SSDs have translated the complexities of colour into hearing or touch. The chapter explores if colour is useful for SSD users, how SSD and veridical colour perception differ and how optimal cross-sensory mappings might be considered. After long-term training, some blind users of SSDs report visual sensations from tactile or auditory stimulation. A related phenomena is that of synaesthesia, a condition where stimulation of one modality (i.e. touch) produces an automatic, consistent and vivid sensation in another modality (i.e. vision). Tactile-visual synaesthesia is an extremely rare variant that can shed light on how the tactile-visual system is altered when touch can elicit visual sensations. Chapter three reports a series of investigations on the tactile discrimination abilities and phenomenology of tactile-vision synaesthetes, alongside questionnaire data from synaesthetes unavailable for testing. Chapter four introduces a new SSD to test if the presentation of colour information in sensory substitution affects object and colour discrimination. Chapter five presents experiments on intuitive auditory-colour mappings across a wide variety of sounds. These findings are used to predict the reported colour hallucinations resulting from LSD use while listening to these sounds. Chapter six uses a new sensory substitution device designed to test the utility of these intuitive sound-colour links for visual processing. These findings are discussed with reference to how cross-sensory links, LSD and synaesthesia can inform optimal SSD design for visual processing

Task-Dependent Masked Priming Effects in Visual Word Recognition

A method used widely to study the first 250 ms of visual word recognition is masked priming: These studies have yielded a rich set of data concerning the processes involved in recognizing letters and words. In these studies, there is an implicit assumption that the early processes in word recognition tapped by masked priming are automatic, and masked priming effects should therefore be invariant across tasks. Contrary to this assumption, masked priming effects are modulated by the task goal: For example, only word targets show priming in the lexical decision task, but both words and non-words do in the same-different task; semantic priming effects are generally weak in the lexical decision task but are robust in the semantic categorization task. We explain how such task dependence arises within the Bayesian Reader account of masked priming (Norris and Kinoshita, 2008), and how the task dissociations can be used to understand the early processes in lexical access