Browsing by Subject "Normalization"

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Open Access
Behavioral and neural investigation on the effect of spatial attention on surround suppression
(2023-09) Kınıklıoğlu, Merve
When a visual stimulus is presented together with other stimuli surrounding it, behavioral sensitivity and neural responses may change, often reduce, compared to when the same stimulus is presented alone. This is commonly referred to as center-surround interaction or surround suppression, and it is one of the most fundamental mechanisms in biological vision. It is well documented that in motion perception, center-surround interaction is affected by the size and contrast of the stimulus. As the size of a drifting grating increases, motion direction discrimination performance, as well as neural activity in one of the main cortical motion processing areas, medial temporal complex (MT+), decreases if the grating has high contrast (surround suppression). Whereas, when the size increases within certain limits, both the discrimination performance and the neural activity in MT+ may increase if the grating has low contrast (surround facilitation). On the other hand, spatial attention is known to modulate surround suppression both in humans and non-human animals with static stimuli. No previous study, how-ever, has directly and systematically investigated the effect of the spatial extent of attention on surround suppression in human motion perception. The studies presented in this dissertation aim to investigate the effect of the extent of spatial attention on center-surround interaction in visual motion processing. In our experiments, we used two attention conditions and a novel stimulus design, where a ‘center’ and a ‘surround’ drifting grating were presented to the participants. Under one of the attention conditions, which we call the ‘narrow-attention’ condition, participants performed a task that limited their attention to the central part of the stimulus. Under the other attention condition, which we call the ‘wide-attention’ condition, participants performed tasks that required them to extend their attention to both the center and surround gratings. Using this experimental paradigm, we measured motion direction discrimination thresholds behaviorally and cortical activity with fMRI. Behaviorally, we found increased thresholds, that is, stronger surround suppression, under the wide attention condition. In the hu-man homolog of MT+ (hMT+), we found that increasing the spatial extent of attention leads to reduced cortical responses, that is, to stronger neural suppression. This was not the case for the activity in the primary visual cortex (V1). Finally, we show that a parsimonious computational model that incorporates spatial attention and response normalization can successfully predict the response patterns in hMT+ and V1. Furthermore, the model could provide a link between cortical responses and behavioral thresholds. Overall, our findings and analyses showed that the behavioral effect can be successfully predicted by hMT+ activity. These results reveal the critical role of spatial attention on surround suppression, namely that surround suppression in motion perception becomes stronger with a wider attention field, and reveal possible cortical mechanisms underpinning the effect.
Open Access
Identification of Novel Reference Genes Based on MeSH Categories
(PLoS ONE, 2014) Ersahin, T.; Carkacioglu, L.; Can, T.; Konu, O.; Atalay, V.; Cetin Atalay, R.
Transcriptome experiments are performed to assess protein abundance through mRNA expression analysis. Expression levels of genes vary depending on the experimental conditions and the cell response. Transcriptome data must be diverse and yet comparable in reference to stably expressed genes, even if they are generated from different experiments on the same biological context from various laboratories. In this study, expression patterns of 9090 microarray samples grouped into 381 NCBI-GEO datasets were investigated to identify novel candidate reference genes using randomizations and Receiver Operating Characteristic (ROC) curves. The analysis demonstrated that cell type specific reference gene sets display less variability than a united set for all tissues. Therefore, constitutively and stably expressed, origin specific novel reference gene sets were identified based on their coefficient of variation and percentage of occurrence in all GEO datasets, which were classified using Medical Subject Headings (MeSH). A large number of MeSH grouped reference gene lists are presented as novel tissue specific reference gene lists. The most commonly observed 17 genes in these sets were compared for their expression in 8 hepatocellular, 5 breast and 3 colon carcinoma cells by RT-qPCR to verify tissue specificity. Indeed, commonly used housekeeping genes GAPDH, Actin and EEF2 had tissue specific variations, whereas several ribosomal genes were among the most stably expressed genes in vitro. Our results confirm that two or more reference genes should be used in combination for differential expression analysis of large-scale data obtained from microarray or next generation sequencing studies. Therefore context dependent reference gene sets, as presented in this study, are required for normalization of expression data from diverse technological backgrounds. © 2014 Ersahin et al.
Open Access
The portrayal of marijuana on vice.com documentaries
(2017-09) Özsu, Gökçe
This thesis aims to examine the representational attitude of vice.com (or VICE) documentaries covering marijuana, in the context of normalization. In this respect, this thesis mainly descriptively analyses three VICE documentaries covering marijuana in the setting of recreation, medicine and industry. VICE is a United States based media outlet which uses hybrid form of journalism combining conventional form of media operations and new media techniques. Normalization is a sociological concept for describing the the scale of social acceptance as a norm which was disseminated from the margins of the society towards mainstream scale. To implement descriptive analysis on vice.com documentaries, normalization and drug representation in the United States media has been evaluated in the socio-historical setting, and examined. As a major finding, even though vice.com documentaries represent marijuana as normal, the normative references of normalization of marijuana is not clear. In this respect, in the conclusion, the determiners and normative background of normalization of marijuana are tried to be discussed.
Open Access
Rape discourses in Turkey : the case of Turkish television series Fatmagül'ün Suçu Ne?
(2012) Yener, Yasemin
The television series Fatmagül’ün Suçu Ne?, which first aired in September 2010, turned in to a phenomenon. The rape scene in the first episode was anticipated for months and after it aired, scene was talked about for very long time. In mass media, series was addressed widely. There were many different criticisms regarding the rape scene. Mainly, it was blamed for vividly representing the act of rape, thus encouraging and rape and humiliating women in various newspaper articles. However, while doing so, newspapers employed a number of rhetoric that may be elucidated as normalization of rape discourse through concealing by deceiving and trivializing rape. In this study, newspaper articles related to Fatmagül’ün Suçu Ne? published in Zaman, Hürriyet, Posta, Radikal and Cumhuriyet newspapers are studied and evaluated in terms of discourse they employ in order to determine rape discourses in Turkish newspapers.
Open Access
Use of DCR-optimized natural switching surfaces in the second-order sliding mode control of DC/DC buck and boost converters and current limiting methods
(2024-08) Altunsoy, Mert
Second-order sliding mode control utilizing natural switching surfaces has demon-strated robust dynamic performance in the control of switching buck and boost converters for start-up, load changes, and large signal disturbances. However, practical implementation often encounters challenges such as the chattering phenomenon and large inductor currents during start-up or loading transients. The primary focus of this research is proposing potential solutions for these practical issues. Assuming the parasitic resistances, such as the on-state resistances of switches and the equivalent series resistances of output capacitors, are relatively low, the direct current resistance (DCR) of the inductor becomes the primary parasitic resistance that causes chattering due to its damping effect. For this reason, the DCR of the inductor is taken into account in the system dynamics from which natural switching surfaces are derived. By incorporating these surfaces into the control laws, the chattering effect caused by losses is mitigated while maintaining effective control. Furthermore, current limiting techniques are proposed for converter protection and reliability. These techniques are integrated into the control laws to manage large inductor currents effectively during transients, thereby pre-venting potential damage and enhancing the overall performance of the converter. Through theoretical analysis, geometrical representations, and simulation studies, a comprehensive framework for minimizing chattering and managing large inductor currents in the second-order sliding mode control of buck and converters integrating natural switching surfaces is established.
Open Access
Use of natural switching in the boundary control of DC/DC buck and boost converters
(2021-08) Koç, Yunus Emre
DC-DC converters are extensively used in many power electronics applications such as photovoltaic systems, wind energy systems, DC motor drives, mobile devices, electric vehicles, etc. Fundamental performance criteria in these appli-cations include tight line and load regulation, low output voltage ripple, high eﬃciency and fast response to load uncertainties. Also, the trade-oﬀ between high performance and component sizes must be considered. In order to meet these requirements, a boundary control method is developed for the resistive loaded buck and boost DC-DC converters. First, normalized plant models are obtained for both converters. The normalization generalizes the controller design by making it independent of the circuit parameters. Then, natural phase plane trajectories of the systems are derived in the normalized domain. Using the nat-ural trajectories of the converters as switching surfaces, special boundary control laws are deﬁned. Switches in the systems are driven by control inputs generated according to the control laws. Via this boundary control method, the fast dy-namic response is provided by utilizing passive components that take up the most space, namely inductor and capacitor, at their theoretical limits. This allows the overall circuit size to be kept small. Finally, the control laws are altered by a small factor so that in steady state, ﬁnite and controlled frequency operation and known ripple magnitudes of system states are obtained. In this way, a common problem in boundary control applications called chattering is eliminated. It is shown via simulations that the proposed controllers manage to recover from load and start-up transients by single switching action for both converters.