Here it is important to understand sanna. Through grasping there is the idea/ thought/feeling, that there is I ,a firm belief. When one opens the mind without nimiitta to infinity, one observes I manifestation and the firmness of belief of I. As one continues to observe this way, one sees ,as cause and effect, the pahana sanna, with anitta/ anatta sanna. Slowly one realises what has arisen, what is perceived through the senses is already dead, what is grasped and identified as I, ever so Important. Then slowly one realises emptiness devoid of self.