Kolmogorov-sinai causality in chaotically intertwined dynamics: A heart rate variability case study

When a system with a traditional u/y input/output pair is embedded in a complex environment, the relative role of the input and the output becomes interchangeable. Here we devise a Kolmogorov-Sinai mutual information approach to determine whether u or y is the "cause" and the other the "effect." It turns out that in some complex environments the information flow goes both ways, a phenomenon that can be abstracted as a feedback structure. The concept is illustrated on the RR/QT coupled dynamics of the heart.