Browsing by Subject "Vision"
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Item Open Access A large video set of natural human actions for visual and cognitive neuroscience studies and its validation with fMRI(MDPI, 2022-12-29) Ürgen, Burcu Ayşen; Nizamoğlu, Hilal; Eroğlu, Aslı; Orban, G. A.The investigation of the perception of others’ actions and underlying neural mechanisms has been hampered by the lack of a comprehensive stimulus set covering the human behavioral repertoire. To fill this void, we present a video set showing 100 human actions recorded in natural settings, covering the human repertoire except for emotion-driven (e.g., sexual) actions and those involving implements (e.g., tools). We validated the set using fMRI and showed that observation of the 100 actions activated the well-established action observation network. We also quantified the videos’ low-level visual features (luminance, optic flow, and edges). Thus, this comprehensive video set is a valuable resource for perceptual and neuronal studies.Item Open Access Beyond Bouma's window: how to explain global aspects of crowding?(Public Library of Science, 2019-05) Doerig, A.; Bornet, A.; Rosenholtz, R.; Francis, G.; Clarke, Aaron M.; Herzog, M. H.In crowding, perception of an object deteriorates in the presence of nearby elements. Although crowding is a ubiquitous phenomenon, since elements are rarely seen in isolation, to date there exists no consensus on how to model it. Previous experiments showed that the global configuration of the entire stimulus must be taken into account. These findings rule out simple pooling or substitution models and favor models sensitive to global spatial aspects. In order to investigate how to incorporate global aspects into models, we tested a large number of models with a database of forty stimuli tailored for the global aspects of crowding. Our results show that incorporating grouping like components strongly improves model performance. Author summary Visual crowding highlights interactions between elements in the visual field. For example, an object is more difficult to recognize if it is presented in clutter. Crowding is one of the most fundamental aspects of vision, playing crucial roles in object recognition, reading and visual perception in general, and is therefore an essential tool to understand how the visual system encodes information based on its retinal input. Hence, classic models of crowding have focused only on local interactions between neighboring visual elements. However, abundant experimental evidence argues against local processing, suggesting that the global configuration of visual elements strongly modulates crowding. Here, we tested all available models of crowding that are able to capture global processing across the entire visual field. We tested 12 models including the Texture Tiling Model, a Deep Convolutional Neural Network and the LAMINART neural network with large scale computer simulations. We found that models incorporating a grouping component are best suited to explain the data. Our results suggest that in order to understand vision in general, mid-level, contextual processing is inevitable.Item Restricted Bir eğitim gönüllüsü: Erol Üçer(Bilkent University, 2024) Demirkaya, Alperen; Kılıç, Aslı; Sıdar, Başar; Gül, Efe Barış; Aydın, MertkanBu makale Türkiye'nin eğitiminin gelişmesinde önemli katkılarda bulunan Erol Üçer'in hayatı, vizyonu ve etkisi üzerine bir inceleme sunmaktadır. Makale, Üçer'in kimliği, eğitim vizyonu ve bu vizyonu nasıl desteklediği konularına odaklanarak başlamaktadır. Ardından, ALEV'in kuruluş süreci ve amacı ele alınmakta, Üçer'in vakıf içinde ve dışında yaptığı eğitim faaliyetleri incelenmektedir. Bununla birlikte ALEV'in kuruluş dönemindeki AAL’in durumu ve vakfın nasıl destek topladığı konuları da ele alınmaktadır. Makalenin son kısımlarında, Erol Üçer'in vefatının ardından ALEV'in geleceği ve bugünkü durumu değerlendirilmektedir. Bu araştırma Erol Üçer'in eğitimdeki önemli katkılarını ve mirasını derinlemesine inceleyerek, onun etkisini ve mirasının günümüzdeki eğitim ortamındaki yansımalarını vurgular.Item Open Access Border ownership selectivity in human early visual cortex and its modulation by attention(Society for Neuroscience, 2009) Fang, F.; Boyacı, Hüseyin; Kersten, D.Natural images are usually cluttered because objects occlude one another. A critical aspect of recognizing these visual objects is to identify the borders between image regions that belong to different objects. However, the neural coding of border ownership in human visual cortex is largely unknown. In this study, we designed two simple but compelling stimuli in which a slight change of contextual information could induce a dramatic change of border ownership. Using functional MRI adaptation, we found that border ownership selectivity in V2 was robust and reliable across subjects, and it was largely dependent on attention. Our study provides the first human evidence that V2 is a critical area for the processing of border ownership and that this processing depends on the modulation from higher-level cortical areas.Item Open Access Cornea engineering on polyester carriers(John Wiley & Sons, Inc., 2006) Zorlutuna, P.; Tezcaner, A.; Kiyat, I.; Aydınlı, Atilla; Hasirci, V.In this study, biodegradable polyester based carriers were designed for tissue engineering of the epithelial and the stromal layers of the cornea, and the final construct was tested in vitro. In the construction of the epithelial layer, micropatterned films were prepared from blends of biodegradable and biocompatible polyesters of natural (PHBV) and synthetic (P(L/DL)LA) origin, and these films were seeded with D407 (retinal pigment epithelial) cells. To improve cell adhesion and growth, the films were coated with fibronectin. To serve as the stromal layer of the cornea, highly porous foams of P(L/DL)LA-PHBV blends were seeded with 3T3 fibroblasts. Cell numbers on the polyester carriers were significantly higher than those on the tissue culture polystyrene control. The cells and the carriers were characterized scanning electron micrographs showed that the foam was highly porous and the pores were interconnected. 3T3 Fibroblasts were distributed quite homogeneously at the seeding site, but probably because of the high thickness of the carrier (∼6 mm); they could not sufficiently populate the core (central parts of the foam) during the test duration. The D407 cells formed multilayers on the micropatterned polyester film. Immunohistochemical studies showed that the cells retained their phenotype during culturing; D407 cells formed tight junctions characteristic of epithelial cells, and 3T3 cells deposited collagen type I into the foams. On the basis of these results, we concluded that the micropatterned films and the foams made of P(L/DL)LA-PHBV blends have a serious potential as tissue engineering carriers for the reconstruction of the epithelial and stromal layers of the cornea.Item Open Access Feedforward and feedback processes in vision(Frontiers Research Foundation, 2015) Kafalıgönül, Hulusi; Breitmeyer, Buruno G.; Öğmen, Haluk[No abstract available]Item Open Access Haptic and visual dimensions of perceived softness(Bilkent University, 2017-09) Üstün, Fatma SeyhunExploring the environment with our senses is a prerequisite to successfully and efficiently interact with it. Our senses provide information about what material objects and surfaces are made of and help us to stay clear of icy patches or using the right grip of force when grasping an oily bottle. Compared to other material properties, the perception of softness has received only limited attention in the haptic and visual perception studies. Moreover, in the haptic domain, softness had been thought of synonymously with compliance. Yet, softness can have many dimensions: the softness of silk and jelly are quite different. Although silk and jelly comply with the force that is applied to them in a similar manner, the perception of softness for these compliant materials are quite different. Using a rating task we investigate here the haptic dimensions of perceived softness and compare it to the haptic dimensions derived from vision only. Results of an exploratory factor analysis suggest that for our set of stimuli, softness has indeed more than one qualitative dimension, i.e. compliance, to it. However, factor loadings were more distinct for the haptic domain. Haptic and visual domains provided rather similar information regarding slipperiness, softness, deformability and roughness. There were, however, differences between the two perceptual domains for granularity, stickiness and hairiness. We discuss these results with respect to the role of haptic and visual information in the perception of softness.Item Open Access The involvement of centralized and distributed processes in sub-second time interval adaptation: an ERP investigation of apparent motion(Blackwell Publishing Ltd, 2017) Kaya, Utku; Yildirim, Fazilet Zeynep; Kafaligonul, HulusiAccumulating evidence suggests that the timing of brief stationary sounds affects visual motion perception. Recent studies have shown that auditory time interval can alter apparent motion perception not only through concurrent stimulation but also through brief adaptation. The adaptation after-effects for auditory time intervals was found to be similar to those for visual time intervals, suggesting the involvement of a central timing mechanism. To understand the nature of cortical processes underlying such after-effects, we adapted observers to different time intervals using either brief sounds or visual flashes and examined the evoked activity to the subsequently presented visual apparent motion. Both auditory and visual time interval adaptation led to significant changes in the ERPs elicited by the apparent motion. However, the changes induced by each modality were in the opposite direction. Also, they mainly occurred in different time windows and clustered over distinct scalp sites. The effects of auditory time interval adaptation were centred over parietal and parieto-central electrodes while the visual adaptation effects were mostly over occipital and parieto-occipital regions. Moreover, the changes were much more salient when sounds were used during the adaptation phase. Taken together, our findings within the context of visual motion point to auditory dominance in the temporal domain and highlight the distinct nature of the sensory processes involved in auditory and visual time interval adaptation. © 2017 Federation of European Neuroscience Societies and John Wiley & Sons LtdItem Restricted İstanbul’dan Bursa’ya: Aykut Hamzagil’in tekstil hikayesi(Bilkent University, 2023) Saraçer,Begüm; Özsu,Defne; Ateşoğlu,Irmak; Özünaldım,Selin; Gürhan,ZeynepBu makalede, Türkiye tekstil sektörünün öncü isimlerinden biri olan Aykut Hamzagil’in, 1970’li yılların başından itibaren tekstil sektöründe yer aldığı konum ele alındı. Bu makale, Türkiye tekstil sektörünün öncü isimlerinden biri olan Aykut Hamzagil’in 1970’li yılların başından itibaren tekstil sektöründe yer aldığı konumu ve getirdiği yenilikleri incelemektedir. Türkiye’de, 1970’li senelerde tekstil sektöründe büyük bir açık vardı. İnsanların, kısıtlı kumaş seçeneklerine erişimi vardı ve insanlar temel ihtiyaçlarını karşılamakta güçlük çekiyordu. Bu güçlüğü bizzat deneyimleyen Aykut Hamzagil, içinde büyüdüğü tekstil sektörüne bu sefer farklı bir amaç ve vizyonla atıldı. Hamzagil’in hedefi, kendisinin de yaşadığı bu açıkları kapatmaktı. Bu doğrultuda kendi markasını kurdu, markalaştı, mağazalaştı, fabrikalaştı ve tekstil sektöründe birçok ilke imza atarak, Türkiye tekstil sektörüne yeni bir soluk kazandırdı.Item Open Access Perceptual averaging in individuals with autism spectrum disorder(Frontiers Research Foundation, 2016) Corbett,, Jennifer Elise; Venuti, P.; Melcher, D.There is mounting evidence that observers rely on statistical summaries of visual information to maintain stable and coherent perception. Sensitivity to the mean (or other prototypical value) of a visual feature (e.g., mean size) appears to be a pervasive process in human visual perception. Previous studies in individuals diagnosed with Autism Spectrum Disorder (ASD) have uncovered characteristic patterns of visual processing that suggest they may rely more on enhanced local representations of individual objects instead of computing such perceptual averages. To further explore the fundamental nature of abstract statistical representation in visual perception, we investigated perceptual averaging of mean size in a group of 12 high-functioning individuals diagnosed with ASD using simplified versions of two identification and adaptation tasks that elicited characteristic perceptual averaging effects in a control group of neurotypical participants. In Experiment 1, participants performed with above chance accuracy in recalling the mean size of a set of circles (mean task) despite poor accuracy in recalling individual circle sizes (member task). In Experiment 2, their judgments of single circle size were biased by mean size adaptation. Overall, these results suggest that individuals with ASD perceptually average information about sets of objects in the surrounding environment. Our results underscore the fundamental nature of perceptual averaging in vision, and further our understanding of how autistic individuals make sense of the external environment. © 2016 Corbett, Venuti and Melcher.Item Open Access Purkinje images: conveying different content for different luminance adaptations in a single image(Blackwell Publishing Ltd, 2015) Arpa, S.; Ritschel, T.; Myszkowski, K.; Çapin, T.; Seidel, Hans-PeterProviding multiple meanings in a single piece of art has always been intriguing to both artists and observers. We present Purkinje images, which have different interpretations depending on the luminance adaptation of the observer. Finding such images is an optimization that minimizes the sum of the distance to one reference image in photopic conditions and the distance to another reference image in scotopic conditions. To model the shift of image perception between day and night vision, we decompose the input images into a Laplacian pyramid. Distances under different observation conditions in this representation are independent between pyramid levels and pixel positions and become matrix multiplications. The optimal pixel colour can be found by inverting a small, per-pixel linear system in real time on a GPU. Finally, two user studies analyze our results in terms of the recognition performance and fidelity with respect to the reference images. Providing multiple meanings in a single piece of art has always been intriguing to both artists and observers. We present Purkinje images, which have different interpretations depending on the luminance adaptation of the observer. Finding such images is an optimization that minimizes the sum of the distance to one reference image in photopic conditions and the distance to another reference image in scotopic conditions. To model the shift of image perception between day and night vision, we decompose the input images into a Laplacian pyramid. © 2014 The Eurographics Association and John Wiley & Sons Ltd.Item Open Access ResViT: residual vision transformers for multimodal medical ımage synthesis(Institute of Electrical and Electronics Engineers Inc., 2022-04-18) Dalmaz, Onat; Yurt, Mahmut; Çukur, TolgaGenerative adversarial models with convolutional neural network (CNN) backbones have recently been established as state-of-the-art in numerous medical image synthesis tasks. However, CNNs are designed to perform local processing with compact filters, and this inductive bias compromises learning of contextual features. Here, we propose a novel generative adversarial approach for medical image synthesis, ResViT, that leverages the contextual sensitivity of vision transformers along with the precision of convolution operators and realism of adversarial learning. ResViT’s generator employs a central bottleneck comprising novel aggregated residual transformer (ART) blocks that synergistically combine residual convolutional and transformer modules. Residual connections in ART blocks promote diversity in captured representations, while a channel compression module distills task-relevant information. A weight sharing strategy is introduced among ART blocks to mitigate computational burden. A unified implementation is introduced to avoid the need to rebuild separate synthesis models for varying source-target modality configurations. Comprehensive demonstrations are performed for synthesizing missing sequences in multi-contrast MRI, and CT images from MRI. Our results indicate superiority of ResViT against competing CNN- and transformer-based methods in terms of qualitative observations and quantitative metrics.Item Open Access Ultrafast on-site selective visual detection of TNT at sub-ppt level using fluorescent gold cluster incorporated single nanofiber(Royal Society of Chemistry, 2015) Senthamizhan, A.; Celebioglu A.; Uyar, TamerIn this communication, a fluorescent gold cluster incorporated electrospun nanofibrous membrane and single nanofiber for selective and sensitive detection of TNT at sub-ppt level are demonstrated.