Kontrast algısının bağlama göre değişiminin araştırılması.

The present study has employed psychophysics and functional magnetic resonance imaging (fMRI) methodologies. The aim of the study is to investigate the role of bottom-up and top-down processing of luminance in contrast perception. In particular, since it is thought that visual illusions occur as a result of top-down processing by means of visual context, the present study investigates how luminance in context affects contrast perception by using brightness illusion. In other words, the purpose of the study is to understand whether physical or perceived properties of luminance dictate contrast perception. An illusory stimulus which was especially created for the present study was used in the experiments. Two psychophysical experiment series and one fMRI experiment series was conducted. In the first experimental series, brightness value of the illusory stimulus was measured with several methods and experimental designs to be sure that illusion is strong enough. In the second experiment series, contrast perception was measured by locating a rectified square-wave grating on the illusory stimulus. In the fMRI experiment series, neuronal correlates of psychophysical results were investigated. Results show that perceived properties of luminance has an effect on contrast perception. Furthermore, fMRI findings showed complicated results both favouring physical and perceptual properties in different conditions.M.S. - Master of Scienc

Bağlama dayalı açıklığın kontrast saptama ve tanımlama üzrindeki etkisi ve bu etkinin nöral korelasyonları

Cataloged from PDF version of article.Thesis (Ph.D.): Bilkent University, Department of Neuroscience, İhsan Doğramacı Bilkent University, 2017.Includes bibliographical references (leaves 92-100).Perceived contrast of a grating varies with its background (or mean) luminance: of the two gratings with the same photometric contrast the one on higher luminance background appears to have higher contrast. On the other hand, context often causes a large perceived difference between equiluminant regions (e.g., simultaneous brightness contrast). Does perceived contrast also vary with contextdependent background lightness even when the luminance remains constant? In this study, the effect of context-dependent lightness on contrast perception was investigated using psychophysical and functional magnetic resonance imaging (fMRI) methods. First, we measured appearance judgments of participants and demonstrated that context-dependent lightness of background in uences the perceived contrast of rectified gratings. Perceived contrast of gratings superimposed on equiluminant but perceptually lighter background is higher compared to ones on perceptually darker backgrounds. However, this pattern is valid only for incremental, not for decremental contrast. Literature indicates a significant difference between visual processing near and above threshold. Also, behaviorally it has been shown that appearance and threshold tasks are mediated by different mechanisms. Therefore, here, we also measured the effect of context-dependent lightness on contrast detection and discrimination thresholds using a 2-IFC procedure. Results indicate that both detection and discrimination thresholds are lower for the gratings superimposed on perceptually lighter backgrounds. Differently from the appearance results, the effect was observed both for incremental and decremental contrast. In an fMRI study, we investigated whether activity in any brain region correlates with background-lightness-dependent contrast perception. Although our stimulus was physically identical, we observed difference in BOLD response within pre-defined region of interests (ROIs) in different visual areas. Both for incremental and decremental contrast, activation, especially in V1, was greater when the grating was superimposed on lighter background for all the contrast levels tested. Variation in V1 activity with varying contrast links better with the detection and discrimination thresholds than the appearance results. Therefore, this study might offer a neural evidence for dissociation between the mechanisms underlying detection (threshold) and identification (appearance) measures. However, the relationship between the threshold and fMRI data does not really agree with the previous findings in literature. These results indicate that the neural activation caused by the detection mechanism may change depending on the absolute or perceived value of the contrast.by Zahide Pamir Karatok.Ph. D

Picturing asthma in Turkey: results from the Turkish adult asthma registry

Introduction: National data on asthma characteristics and the factors associated with uncontrolled asthma seem to be necessary for every country. For this purpose, we developed the Turkish Adult Asthma Registry for patients with asthma aiming to take a snapshot of our patients, thereby assigning the unmet needs and niche areas of intervention. Methods: Case entries were performed between March 2018 and March 2022. A web-based application was used to record data. Study outcomes were demographic features, disease characteristics, asthma control levels, and phenotypes. Results: The registry included 2053 patients from 36 study centers in Turkey. Female subjects dominated the group (n = 1535, 74.8%). The majority of the patients had allergic (n = 1158, 65.3%) and eosinophilic (n = 1174, 57.2%) asthma. Six hundred nineteen (32.2%) of the patients had obese asthma. Severe asthma existed in 670 (32.6%) patients. Majority of cases were on step 3–5 treatment (n: 1525; 88.1%). Uncontrolled asthma was associated with low educational level, severe asthma attacks in the last year, low FEV1, existence of chronic rhinosinusitis and living in particular regions. Conclusion: The picture of this registry showed a dominancy of middle-aged obese women with moderate-to-severe asthma. We also determined particular strategic targets such as low educational level, severe asthma attacks, low FEV1, and chronic rhinosinusitis to decrease uncontrolled asthma in our country. Moreover, some regional strategies may also be needed as uncontrolled asthma is higher in certain regions. We believe that these data will guide authorities to reestablish national asthma programs to improve asthma service delivery

Characteristics of asthma in an older adult population according to sex and control level: why are asthma symptoms in older women not well-controlled?

ObjectiveThe older adult population in Turkey has increased by 22.6% in the last 5 years, and the characteristics of such patients with asthma remain uninvestigated. Therefore, we aimed to evaluate the characteristics of older adults with asthma according to sex and asthma control status to provide an in-depth overview of asthma in this population in Turkey.MethodsThe data of older adults (age 65 years and over) with asthma were obtained from a multicenter, cross-sectional asthma database registry (Turkish Adult Asthma Registry, TAAR) funded by the Turkish Thoracic Society. Comparisons were made based on sex and asthma control levels using the Global Initiative for Asthma (GINA) Asthma Symptom Control Questionnaire.ResultsOf the 2053 (11.5%) patients registered with the TAAR, 227 were older adults (median age, 69 (8), women, 75.8% (n = 172)). Of these, 46.5% (n = 101) had obesity to some degree. Compared with men, women had lower education, income levels, and employment rates. Additionally, women exhibited a higher prevalence of obesity, hypertension, and thyroid gland disease than men. Being female (OR: 2.99; 95% CI: 1.307-6.880), the presence of gastroesophageal reflux disease (OR: 2.855; 95% CI: 1.330-6.130), and a predicted forced expiratory volume in the first-second value lower than 80% (OR: 2.938; 95% CI: 1.451-5.948) were associated with poorly controlled asthma.ConclusionsHerein, older adults comprised 11.5% of adult patients with asthma. Being female poses a disadvantage in terms of both asthma prevalence and control in the older adult asthmatic population owing to the prevalence of comorbidities and socioeconomic sex-related distinguishing factors