Multiscale Bayesian state-space model for Granger causality analysis of brain signal

Modelling time-varying and frequency-specific relationships between two brain signals is becoming an essential methodological tool to answer theoretical questions in experimental neuroscience. In this article, we propose to estimate a frequency Granger causality statistic that may vary in time in order to evaluate the functional connections between two brain regions during a task. We use for that purpose an adaptive Kalman filter type of estimator of a linear Gaussian vector autoregressive model with coefficients evolving over time. The estimation procedure is achieved through variational Bayesian approximation and is extended for multiple trials. This Bayesian State Space (BSS) model provides a dynamical Granger-causality statistic that is quite natural. We propose to extend the BSS model to include the à trous Haar decomposition. This wavelet-based forecasting method is based on a multiscale resolution decomposition of the signal using the redundant à trous wavelet transform and allows us to capture short- and long-range dependencies between signals. Equally importantly it allows us to derive the desired dynamical and frequency-specific Granger-causality statistic. The application of these models to intracranial local field potential data recorded during a psychological experimental task shows the complex frequency-based cross-talk between amygdala and medial orbito-frontal cortex.     

The proliferation of alternative film exhibition spaces in Istanbul: cultural segregation and urban cinephilia

In the last decade, Istanbul witnessed the rapid proliferation of alternative film exhibition spaces such as museums, cafes, art and cultural centres in specific neighbourhoods. This increase is a result of mostly three forces: the monopoly of dominant distribution companies, authoritarian pressure of the government and urban transformation in Istanbul. These places provide space for censored films and are essentially important for independent and experimental films as well as documentaries and short films which have very limited or no theatrical release. On the other hand, their concentration in specific districts and that they target the audience with certain cultural capital is aggregate hierarchical clusters. Through analysing these alternative exhibition spaces in Istanbul, this study investigates the changing relationship between film exhibition, audience and the city. It discovers how urban transformation, authoritarian cultural policies and economic capital changed cinema-going and urban cinephilia in Istanbul. It suggests that while these alternative film exhibiton venues provide space for independent filmmakers, festivals and censored films, they also articulate to social hierarchy and cultural segregation.