Browsing by Subject "RSA"
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Item Open Access Perception of built environments and its neural modulation by the behavioral goals of the perceiver(Bilkent University, 2023-07) Koç, Aysu NurA scene is a view of an environment with a spatial layout one can act within. Scene perception has been studied extensively in the neuroscience literature, examining changes in neural activity across the brain and scene-selective regions (PPA, RSC, OPA), in response to various low and high-level features and tasks. The focus of the field has been mostly on outdoor scenes based on broad categorical differences (e.g. natural/man-made) or basic differences between otherwise similar indoor environments (e.g. ceiling height) and behavioral components regarding scene perception have been overlooked. Interactions with fields such as environ-mental psychology or neuroarchitecture, which could inspire a more ecologically valid study of scenes, are rare. Hereby, we investigated the perception of built environments where we spend most of our time, drew our categorization method from the architecture literature, and employed multiple tasks. The categories were elements that (i) allow our access to and circulation within environments (entrances, exits, corridors, stairs); and that (ii) do not directly aid locomotion but rather serve human needs (restrooms, eating and seating areas). FMRI scans were obtained from 23 participants as they viewed scenes from built environments and performed two tasks: a categorization task based on the main afforded action differences between the defined categories, and an approach-avoidance task where participants decided to enter the scene or not, measuring the initial action regarding an environment. Scene-selective ROIs were defined with a localizer session. Univariate analyses did not reveal strong differences between the tasks. Searchlight MVPA revealed categories, but not tasks, are classified at the whole-brain level, at the lingual and parahippocampal gyri, the SMA, and the occipital cortex. Model-based RSA at the ROI level revealed that tasks modulate activation patterns to built environments in all three ROIs, but do not entirely explain them, whereas categorical and visual models did not correlate with the activation patterns in any of these regions. We utilize an interdisciplinary perspective to scene perception to expand the ecological validity of the stimuli and task con-tent, showing that neural responses to built environments are modulated by the behavioral goals of the observer at the ROI level, and stimulus category at the whole-brain level.Item Open Access Robust threshold schemes based on the Chinese remainder theorem(Springer, 2008-06) Kaya, Kamer; Selçuk, Ali AydınRecently, Chinese Remainder Theorem (CRT) based function sharing schemes are proposed in the literature. In this paper, we investigate how a CRT-based threshold scheme can be enhanced with the robustness property. To the best of our knowledge, these are the first robust threshold cryptosystems based on a CRT-based secret sharing. © 2008 Springer-Verlag Berlin Heidelberg.Item Open Access The interplay of prior information and motion cues in resolving visual ambiguity in agent perception(Bilkent University, 2023-08-06) Elmas, Sena ErAgent perception, a complex cognitive task that involves interpreting an agent’s actions to infer their internal states and adjust our behavior accordingly, is a fundamental aspect of human cognition. Despite its importance, a significant gap persists in our understanding of how low-level factors, such as motion and form information, interact with top-down factors, such as prior information about the agents. To address this gap, we conducted two electroencephalogram (EEG) experiments investigating the interplay of prior knowledge and motion information on the temporal dynamics of agent perception in the human brain. We used human, android and robot agents engaged in various actions. The chosen agents were designed to form a set wherein form information alone could not easily resolve the ambiguity in agent identities. In the first experiment, participants were informed about agent identities be-fore the experiment (Prior Experiment), while in the second experiment, participants remained uninformed (Naive Experiment). We controlled the availability of motion information by presenting stimuli in either video and image formats. We recorded scalp EEG and utilized event-related potential (ERP) analysis and model-based representational similarity analysis (RSA) to uncover the temporal course of agent representation in the human brain. Our results revealed that the processing of agents in EEG depends on the availability of motion information and prior information. Specifically, in the Naive Experiment, agent information was available longer during the still condition than in the moving condition. In contrast, agent information was present for similar durations in still and moving conditions of the Prior Experiment. These findings suggest that prior knowledge and motion information interactively modulate the duration of the processing of agent information. Our results underscore the critical role of prior knowledge and motion cues in shaping the processing of agent information, highlighting the complex interplay between top-down modulation and bottom-up cues in driving the perception of agents and their actions. This study contributes to our understanding of the temporal dynamics of agent perception and the role of top-down and bottom-up processes in this complex cognitive task.Item Open Access Threshold cryptography based on Asmuth–Bloom secret sharing(Elsevier Inc., 2007-10-01) Kaya, K.; Selçuk, A. A.In this paper, we investigate how threshold cryptography can be conducted with the Asmuth-Bloom secret sharing scheme and present three novel function sharing schemes for RSA, ElGamal and Paillier cryptosysterns. To the best of our knowledge, these are the first provably secure threshold cryptosystems realized using the Asmuth-Bloom secret sharing. Proposed schemes are comparable in performance to earlier proposals in threshold cryptography. (c) 2007 Elsevier Inc. All rights reserved.