DTF

The determination of the biological signals propagation and in particular directions of flow of the brain activity are crucial for the understanding of information processing in organisms. Several methods have been proposed for estimation of the directionality, however they were defined for two channels only. When larger set of interacting channels is involved bivariate estimates lead to erroneous results. DTF -- Directed Transfer Function (Kamiński and Blinowska 1991 [1]) takes into account all channels of process simultaneously and makes possible estimation of activity flow in given direction as a function of frequency. It is based on the concept of Granger causality [13] extended for arbitrary number of channels (Kamiński et al. 2001 [3]). DTF is robust in respect to noise and constant phase disturbances, in particular it discriminates against volume conduction, which propagates with zero phase. Short-time Directed Transfer Function (SDTF) makes possible calculation of activity flow as a function of time and frequency, when multiple realizations of the process are available (e. g. event related responses).