By introducing the conflicting effects of dynamic changes in blood flow,volume and blood oxygenation,Balloon model provides a biomechanical compelling interpretation of the BOLD signal.In order to obtain optimal estimates for both the states and parameters involved in this model,a joint filtering (estimate) method has been widely used [1,2].However,it is flawed in several aspects: (i) Correlation or interaction between the states and parameters is incorporated despite its nonexistence in biophysical reality.(ii) A joint representation for states and parameters necessarily means the large dimension of state space and will in turn lead to huge numerical cost in implementation.Given this knowledge,a dual filtering approach is proposed and demonstrated in this paper as a highly competent alternative,which can not only provide more reliable estimates,but also in a more efficient way.The two approaches in our discussion will be based on unscented Kalman filter [3,4],which has become the algorithm of choice in numerous nonlinear estimation and machine learning applications.