For our purposes, perception as a statistic on Arx represents how alert a character typically is and how likely they are to notice anything out of the ordinary or detect anything is amiss. This could be noticing that the masked group of armed men steadily surrounding you is up to no good (low perception), or that the single grain of sand is out of place on a shore so obviously that's the way the ruffians fled. As a scale:
0:Ever been in a sensory deprivation chamber? These guys are less aware of their surroundings.
1: "Was that a bird? Was it a dragon? No seriously I'm asking, I have no idea."
2: Average human, sometimes they won't see the stampede coming at them, and sometimes they'll see that missing needle in the haystack.
3: That smug individual that sees through optical illusions immediately every time.
4: Eyes in the back of their head. Not literally. That'd be creepy.
5: The hero in the story that no matter the circumstances, no ambush will ever work on them.
6: Gets annoyed that Sherlock still hasn't noticed what they saw.