Introverted Sensation deals primarily with interpreting the present dynamics of the environment according to personal experience and knowledge. Therefore, the dynamics of the environment affect the ego (instead of the inverse with Pe users). An example of this would be, as I've mentioned prior, an Si-using ex-con hearing police sirens and immediately associating polices sirens with his personal experience in prison (perhaps he was arrested after a hot pursuit where sirens blared everywhere), possibly evoking emotions such as fear or anxiety even if the police are not actually after him. Usually, Si measures the dynamics of the environment according to how comfortable they are (or how stable they are, to counterbalance the unpredictability of underdeveloped Ne), and in this specific example, the police sirens make the ex-con nervous (environment affects ego).
Introverted Intuition on the other hand, deals with interpreting the hypothetical dynamics of the environment, or, in a more concise manner, why the environment is the way it is now, and where the environment is probably leading to in the future. Introverted Intuitives don't actively pay attention to the dynamics of the present environment then, and are wholly focused on the causation of the environment and the cause-effect relationships between objects in the environments. Usually, Ni analyzes components of the environment via their static, unchanging qualities (Se, static-dynamic is a dichotomy in another system) and attempts to provide a probable perspective of why an object or the environment has those static qualities. A huge dent on the right side of a car for instance, might tell an Introverted Intuitive that the car was involved in an accident where the driver of the car turned left into oncoming traffic (as all other possible scenarios are unlikely and wishful thinking). Introverted Intuitives have an inferiority complex, however, when it comes to affecting the environment in the immediate present (Se inf.).