Perception is the way we interpret the information we sense. The way we interpret the world in many ways dictates our sense of reality. Even if our senses are keen if our perception is skewed we will not understand the information we sense. Lets first go over some basic definitions and rules of sensation and perception.
Thresholds are the idea that our senses have limits. First there is the absolute threshold, which is the smallest amount you can just sense something about half of the time. What that means is that if the guy sitting next to you in class farts, and you take a whiff and smell it, but the next whiff do not smell it, then kind of smell it again- the fart is at your absolute threshold for smell.