PLAQUE-TYPE BLUE NEVUS – A SINGULAR VARIANT OF BLUE NEVUS

Introdução: O nevo azul em placa é uma variante rara de nevo azul, surgindo como uma placa azul- -acinzentada de grandes dimensões, frequentemente com aspecto multinodular, habitualmente de evolução congénita ou iniciando-se durante a infância. O seu aspecto clínico e histológico pode confundir-se com o do nevo azul maligno mas o seu prognóstico é geralmente favorável.Caso Clínico: Apresentamos um doente do sexo masculino de 48 anos com lesão em placa azul-acinzentada a negra com cerca de 4x6cm, evoluindo desde o nascimento, com aquisição progressiva de nodularidade até à puberdade e estabilização posterior. À dermatoscopia apresentava uma lesão central de maiores dimensões com padrão sem estrutura, policromático (coloração azul, cinzenta, negra e castanha) e extensas áreas com véu azul-acinzentado, adjacente à qual se observavam pequenos glóbulos-satélite azulados. Realizou biópsia incisional que demonstrou presença de nevo azul comum e posteriormente excisão completa da lesão com demonstração de nevo azul predominantemente comum mas com áreas focalmente celulares, mais profundas. Mantem-se até à data sem evidência de recorrência.Conclusão: Existem múltiplas variantes de nevo azul, sendo o nevo azul em placa uma entidade rara. Recentemente, relatos na literatura apontam para um comportamento biológico incerto com possível recorrência local e ganglionar. Com este caso pretendemos alertar para o reconhecimento desta entidade e para o seu seguimento apropriado.Introduction: Plaque-type blue nevus is a rare variant of blue nevus, presenting usually as blue-gray plaque with superimposed nodules, beginning at birth or in early childhood and becoming stable during puberty. Its clinical, dermoscopic and even histopathological features may be worrisome and distinction from malignant blue nevus can be difficult, although its prognosis is generally favourable.Case Report: We present a 48 year-old male who had a blue-gray plaque with multinodularity arising in the left scapular region. The lesion had been present since birth, becoming stable during adolescence. Dermoscopy revealed a central structureless polychromatic plaque (blue, gray, black and brown areas) and extensive areas of blue-whitish veil. Adjacent to the central lesion, small blue satellite globules could be seen. Incisional biopsy showed a common blue nevus, and complete excision of the lesion confirmed the presence of a blue nevus predominantly of the common type, and focal cellular areas in its deeper portion. The patient is so far free of recurrence.Conclusion: There are many variants of blue nevus, and plaque-type blue nevus is one of the rarest. Classically regarded as having good prognosis, recent case-reports have shown a tendency towards local and lymph-node recurrence, the reason why recognition of this entity and appropriate follow-up are important

Spatial Information in Natural Viewing Behavior and Overt Visual Attention

The ability to visually explore the world is a substantial and crucial factor for humans to interact and navigate in their environment. Given the importance of the visual system, it is no wonder that vision research has become one of the major fields in cognitive science. Eye tracking studies hereby revealed three main factors, that guide our visual perception and attention. These factors can be described as bottom-up and top-down features, as well as spatial properties. Whereas previous research has put a lot of effort in investigating each of these factors in detail, the combined interaction of the factors - especially regarding spatial properties and biases - is less well understood. This thesis deals with the different aspects of several features influencing visual behavior. I present four studies that examine different aspects of images with respect to their spatial properties. Hereby, I elaborate the global salience of images as spatial factor, which can be impacted by top-down features, such as emotions. Further, I describe how the effect of image sizes as a spatial property is linked with visual exploration and exploitation. In study 1 (Chapter 2) we investigated the global salience of images and its properties. While recording of eye movements, participants freely observed several image pairs, where one image has been shown on the left, and one image on the right side of the screen. Based on results of the eye tracking recordings, we trained a logistic regression model to calculate a global salience coefficient for each image that can be ranked in order to predict the location - left or right image - of the first fixations in an image pair. Our trained model was able to accurately predict the first fixation of an image pair, indicating that images indeed provide a unique global salience score. Hereby, we showed that the global salience of an image is independent of local salience and further that a given task or familiarity of the images affected the respective global salience. In study 2 (Chapter 3) we investigated the influence of emotions as top-down factor on natural visual behavior. Participants had been emotionally primed either by a sequence of positive or negative laden images. Afterwards, we recorded participants' eye movements while being confronted with image pairs, were one positive and one negative image - left and right respectively - was presented simultaneously. Results showed that positively primed participants tended to shift overt attention towards negative images in the stimulus pairs. In a later memory request, we further showed that such participants had better recall performance of negative image content. Thus, we concluded that positive priming increases attention and memory towards negative content. In study 3 (Chapter 4) we investigated the trade-off between the exploration (i.e. initiate fixations to unseen image areas) and exploitation (i.e. stay and process the currently fixated information in depth) of natural images with varying sizes. Participants freely observed images of different sizes and categories while eye movements have been recorded. For exploration we tested the distribution of fixations measured by the central tendency and entropy, as well as number of fixations and saccade amplitudes. The exploitation was derivated from the fixation duration. In our results, we found that larger image sizes led to a shift from exploitation towards exploration. That is, images have been explored more broaden while in-depth processing reduced accordingly. In study 4 (Chapter 5) we investigated the effect of image sizes in natural viewing behavior within patients suffering from retinitis pigmentosa (RP); an inherited disease that causes progressive peripheral visual-field loss. The purpose of this study was to examine whether visual behavior differed when the scene content was shown in various extents of the perceived visual field. For this, participants with varying degrees of visual-field loss and healthy control participants freely observed images of different sizes while eye movements were recorded. For healthy control participants we could replicate the effects already described in Chapter 4. That is, larger images lead to a shift from exploitation to exploration. Surprisingly, on group level RP patients scanned the images similar to the healthy control participants. However, on individual level RP patients also showed individual idiosyncratic explorative strategies when the observed scene exceeded their visible field. We thus concluded, that although retinitis pigmentosa leads to a severe loss of the visual field, there seems to be no general adaptive mechanism adapting visual exploration accordingly. Instead, individuals rely on individual strategies, leading to high heterogeneity in the RP group. In a nutshell, our results showed that images provide unique global salience coefficients that can predict attraction of visual attention. However, emotions as top-down factor affect these global salience coefficients as shown by a shift of attention towards negative image content. The size of an image as spatial property affects natural viewing behavior in such way that in-depth processing (exploitation) shifts towards broader exploration in large images. These results remain remarkably stable, even when the image size extends the visual field (in RP patients). Summarized, the studies in this thesis were motivated to gain and deepen knowledge in the interplay between distinct factors - with an emphasis on spatial properties - that impact visual behavior and attention

Global visual salience of competing stimuli

Current computational models of visual salience accurately predict the distribution of fixations on isolated visual stimuli. It is not known, however, whether the global salience of a stimulus, that is its effectiveness in the competition for attention with other stimuli, is a function of the local salience or an independent measure. Further, do task and familiarity with the competing images influence eye movements? Here, we investigated the direction of the first saccade to characterize and analyze the global visual salience of competing stimuli. Participants freely observed pairs of images while eye movements were recorded. The pairs balanced the combinations of new and already seen images, as well as task and task-free trials. Then, we trained a logistic regression model that accurately predicted the location---left or right image---of the first fixation for each stimulus pair, accounting too for the influence of task, familiarity and lateral bias. The coefficients of the model provided a reliable measure of global salience, which we contrasted with two distinct local salience models, GBVS and Deep Gaze. The lack of correlation of the behavioral data with the former and the small correlation with the latter indicate that global salience cannot be explained by the feature-driven local salience of images. Further, the influence of task and familiarity was rather small and we reproduced the previously reported left-sided bias. Summarized, we showed that natural stimuli have an intrinsic global salience related to the human initial gaze direction, independent of the local salience and little influenced by task and familiarity

Global visual salience of competing stimuli

Current computational models of visual salience accurately predict the distribution of fixations on isolated visual stimuli. It is not known, however, whether the global salience of a stimulus, that is, its effectiveness in the competition for attention with other stimuli, is a function of the local salience or an independent measure. Further, do task and familiarity with the competing images influence eye movements? Here, we investigated the direction of the first saccade to characterize and analyze the global visual salience of competing stimuli. Participants freely observed pairs of images while eye movements were recorded. The pairs balanced the combinations of new and already seen images, as well as task and task-free trials. Then, we trained a logistic regression model that accurately predicted the location—left or right image—of the first fixation for each stimulus pair, accounting too for the influence of task, familiarity, and lateral bias. The coefficients of the model provided a reliable measure of global salience, which we contrasted with two distinct local salience models, GBVS and Deep Gaze. The lack of correlation of the behavioral data with the former and the small correlation with the latter indicate that global salience cannot be explained by the feature-driven local salience of images. Further, the influence of task and familiarity was rather small, and we reproduced the previously reported left-sided bias. Summarized, we showed that natural stimuli have an intrinsic global salience related to the human initial gaze direction, independent of the local salience and little influenced by task and familiarity