Browsing by Subject "Motion"

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Ankara Uluslararası Protestan Kilisesi
(Bilkent University, 2020) Kadım, Cankat Anday; Koçak, Doğa; Çelik, Enes; Kaboğlu, Melisa; Ayan, Rüzgar
Şu an bulunduğu binasına 1998 yılında taşınan Ankara Uluslararası Protestan Kilisesi, bu taşınmadan önceki 8 yılda birçok farklı yerde faaliyet göstermiştir. Ankara‟da bulunan yabancılar tarafından 1990 yılında Ankara‟da bir ev topluluğu olarak başlayan ve 1998 yılına kadar bir otel ve bir depo da dahil olmak üzere birkaç farklı yere taşınmak zorunda kalmıştır. 20 Eylül 1998 tarihinde Çiğdem Mahallesi‟nde bulunan kendi binalarına taşınarak Ankara‟da resmi anlamda Türk Hükümeti‟nden izin alınarak kurulan ilk kilise olmuşlardır. Topluluk, bu tarihten beri kendi binasında düzenli olarak olarak ibadete açık haldedir.
Open Access
Attentional modulations of audiovisual interactions in apparent motion: Temporal ventriloquism effects on perceived visual speed
(Springer New York LLC, 2022-08-22) Duyar, Aysun; Pavan, Andrea
The timing of brief stationary sounds has been shown to alter different aspects of visual motion, such as speed estimation. These effects of auditory timing have been explained by temporal ventriloquism and auditory dominance over visual information in the temporal domain. Although previous studies provide unprecedented evidence for the multisensory nature of speed estimation, how attention is involved in these audiovisual interactions remains unclear. Here, we aimed to understand the effects of spatial attention on these audiovisual interactions in time. We utilized a set of audiovisual stimuli that elicit temporal ventriloquism in visual apparent motion and asked participants to perform a speed comparison task. We manipulated attention either in the visual or auditory domain and systematically changed the number of moving objects in the visual field. When attention was diverted to a stationary object in the visual field via a secondary task, the temporal ventriloquism effects on perceived speed decreased. On the other hand, focusing attention on the auditory stimuli facilitated these effects consistently across different difficulty levels of secondary auditory task. Moreover, the effects of auditory timing on perceived speed did not change with the number of moving objects and existed in all the experimental conditions. Taken together, our findings revealed differential effects of allocating attentional resources in the visual and auditory domains. These behavioral results also demonstrate that reliable temporal ventriloquism effects on visual motion can be induced even in the presence of multiple moving objects in the visual field and under different perceptual load conditions.
Open Access
A decision theoretic approach to motion saliency in computer animations
(Springer, Berlin, Heidelberg, 2011) Arpa, Sami; Bülbül, Abdullah; Çapın, Tolga
We describe a model to calculate saliency of objects due to their motions. In a decision-theoretic fashion, perceptually significant objects inside a scene are detected. The work is based on psychological studies and findings on motion perception. By considering motion cues and attributes, we define six motion states. For each object in a scene, an individual saliency value is calculated considering its current motion state and the inhibition of return principle. Furthermore, a global saliency value is considered for each object by covering their relationships with each other and equivalence of their saliency value. The position of the object with highest attention value is predicted as a possible gaze point for each frame in the animation. We conducted several eye-tracking experiments to practically observe the motion-attention related principles in psychology literature. We also performed some final user studies to evaluate our model and its effectiveness. © 2011 Springer-Verlag.
Open Access
Dynamic dot displays reveal material motion network in the human brain
(Elsevier BV, 2021-03) Schmid, A. C.; Boyacı, Hüseyin; Doerschner,Katja
There is growing research interest in the neural mechanisms underlying the recognition of material categories and properties. This research field, however, is relatively more recent and limited compared to investigations of the neural mechanisms underlying object and scene category recognition. Motion is particularly important for the perception of non-rigid materials, but the neural basis of non-rigid material motion remains unexplored. Using fMRI, we investigated which brain regions respond preferentially to material motion versus other types of motion. We introduce a new database of stimuli – dynamic dot materials – that are animations of moving dots that induce vivid percepts of various materials in motion, e.g. flapping cloth, liquid waves, wobbling jelly. Control stimuli were scrambled versions of these same animations and rigid three-dimensional rotating dots. Results showed that isolating material motion properties with dynamic dots (in contrast with other kinds of motion) activates a network of cortical regions in both ventral and dorsal visual pathways, including areas normally associated with the processing of surface properties and shape, and extending to somatosensory and premotor cortices. We suggest that such a widespread preference for material motion is due to strong associations between stimulus properties. For example viewing dots moving in a specific pattern not only elicits percepts of material motion; one perceives a flexible, non-rigid shape, identifies the object as a cloth flapping in the wind, infers the object's weight under gravity, and anticipates how it would feel to reach out and touch the material. These results are a first important step in mapping out the cortical architecture and dynamics in material-related motion processing.
Open Access
Gloss and speed judgments yield different fine tuning of saccadic sampling in dynamic scenes
(Sage Publications, 2019-12) Toscani, M.; Yücel, Ezgi I.; Doerschner, Katja
Image motion contains potential cues about the material properties of objects. In earlier work, we proposed motion cues that could predict whether a moving object would be perceived as shiny or matte. However, whether the visual system uses these cues is still uncertain. Herein, we use the tracking of eye movements as a tool to understand what visual information observers use when engaged in material perception. Observers judged either the gloss or the speed of moving blobby shapes in an eye tracking experiment. Results indicate that during glossiness judgments, participants tend to look at gloss-diagnostic dynamic features more than during speed judgments. This suggests a fine tuning of the visual system to properties of moving stimuli: Task relevant information is actively singled out and processed in a dynamically changing environment.
Open Access
An index structure for moving objects in video databases
(1999) Yavuz, Tuba
Modeling moving objects and Iiandling various types of motion queries are interesting topics to investigate in the area of video databases. In one type of motion queries, motion of multiple objects is specified by the changes in relative spatial positions of objects. Answering such kind of queries, that involve motion of multiple objects whose identifications cire not specified, requires some type of indexing because the time complexity of processing such a query in the absence of an index structure is 0{N \l{N — n)!), where N is the number of objects in the database and n is the number of objects in the query. In this work, we propose a spatio-temporal index structure, which we call ,S'M/A7-index, and compare its performance against a similar scheme proposed in [18]. The scheme presented in [18] consists of a constraint satisfaction algorithm, which is called Join Window Reduction (JW R ), combined with a spatial index structure (R*- tree). Experimental results indicate thcit SMIST-'mdex outperforms the JW R algorithm. Also, SMIST-'mdex is shown to be scalable to increasing number of frames and objects.
Open Access
Leg motion classification with artificial neural networks using wavelet-based features of gyroscope signals
(2011) Ayrulu-Erdem, B.; Barshan, B.
We extract the informative features of gyroscope signals using the discrete wavelet transform (DWT) decomposition and provide them as input to multi-layer feed-forward artificial neural networks (ANNs) for leg motion classification. Since the DWT is based on correlating the analyzed signal with a prototype wavelet function, selection of the wavelet type can influence the performance of wavelet-based applications significantly. We also investigate the effect of selecting different wavelet families on classification accuracy and ANN complexity and provide a comparison between them. The maximum classification accuracy of 97.7% is achieved with the Daubechies wavelet of order 16 and the reverse bi-orthogonal (RBO) wavelet of order 3.1, both with similar ANN complexity. However, the RBO 3.1 wavelet is preferable because of its lower computational complexity in the DWT decomposition and reconstruction. © 2011 by the authors; licensee MDPI, Basel, Switzerland.
Open Access
Monitor: re-imagining the clock tower an artist research on form, chain reaction and duration
(2020-06) Çelebi, Sena
Monitor is a re-imagination of a clock tower, which re-conceptualizes the passing of time in a way that all moving elements inside the city outdoors become the units of the timekeeping activity. Abandoning the conventional approaches that frame time as a homogeneous entity, I make use of Bergson’s description of dura, and rethink the socalled homogeneity rather as a heterogeneous structure composed of distinct durations that are constantly intersecting with each other, and, produce infinite amount of arbitrary arrangements. This thesis offers a concept of an urban media sculpture that mirrors the movement of the people in outdoor settings, by collecting the real-time data from public monitoring systems. In doing so, the theory and the practice became intricate which makes the main focus of this thesis principally to celebrate the process of artistic research.
Open Access
Phase-correcting non-local means filtering for diffusion-weighted imaging of the spinal cord
(John Wiley, 2018) Kafalı, Sevgi Gökçe; Çukur, Tolga; Sarıtaş, Emine Ülkü
Purpose: DWI suffers from low SNR when compared to anatomical MRI. To maintain reasonable SNR at relatively high spatial resolution, multiple acquisitions must be averaged. However, subject motion or involuntary physiological motion during diffusion-sensitizing gradients cause phase offsets among acquisitions. When the motion is localized to a small region, these phase offsets become particularly problematic. Complex averaging of acquisitions lead to cancellations from these phase offsets, whereas magnitude averaging results in noise amplification. Here, we propose an improved reconstruction for multi-acquisition DWI that effectively corrects for phase offsets while reducing noise. Theory and Methods: Each acquisition is processed with a refocusing reconstruction for global phase correction and a partial k-space reconstruction via projection-onto-convex-sets (POCS). The proposed reconstruction then embodies a new phase-correcting non-local means (PC-NLM) filter. PC-NLM is performed on the complex-valued outputs of the POCS algorithm aggregated across acquisitions. The PC-NLM filter leverages the shared structure among multiple acquisitions to simultaneously alleviate nuisance factors including phase offsets and noise. Results: Extensive simulations and in vivo DWI experiments of the cervical spinal cord are presented. The results demonstrate that the proposed reconstruction improves image quality by mitigating signal loss because of phase offsets and reducing noise. Importantly, these improvements are achieved while preserving the accuracy of apparent diffusion coefficient maps. Conclusion: An improved reconstruction incorporating a PC-NLM filter for multi-acquisition DWI is presented. This reconstruction can be particularly beneficial for high-resolution or high-b-value DWI acquisitions that suffer from low SNR and phase offsets from local motion.
Open Access
The Smoluchowski-Kramers limit of stochastic differential equations with arbitrary state-dependent friction
(Springer, 2015) Hottovy, S.; McDaniel, A.; Wehr, J.; Volpe, G.
We study a class of systems of stochastic differential equations describing diffusive phenomena. The Smoluchowski-Kramers approximation is used to describe their dynamics in the small mass limit. Our systems have arbitrary state-dependent friction and noise coefficients. We identify the limiting equation and, in particular, the additional drift term that appears in the limit is expressed in terms of the solution to a Lyapunov matrix equation. The proof uses a theory of convergence of stochastic integrals developed by Kurtz and Protter. The result is sufficiently general to include systems driven by both white and Ornstein-Uhlenbeck colored noises. We discuss applications of the main theorem to several physical phenomena, including the experimental study of Brownian motion in a diffusion gradient.
Open Access
Speckle optical tweezers: micromanipulation with random light fields
(Optical Society of America, 2014-07-18) Volpe, G.; Kurtz, L.; Callegari, A.; Volpe, G.; Gigan, S.
Current optical manipulation techniques rely on carefully engineered setups and samples. Although similar conditions are routinely met in research laboratories, it is still a challenge to manipulate microparticles when the environment is not well controlled and known a priori, since optical imperfections and scattering limit the applicability of this technique to real-life situations, such as in biomedical or microfluidic applications. Nonetheless, scattering of coherent light by disordered structures gives rise to speckles, random diffraction patterns with well-defined statistical properties. Here, we experimentally demonstrate how speckle fields can become a versatile tool to efficiently perform fundamental optical manipulation tasks such as trapping, guiding and sorting. We anticipate that the simplicity of these "speckle optical tweezers" will greatly broaden the perspectives of optical manipulation for real-life applications. (C) 2014 Optical Society of America