I tend to use Perception as the act of Investigation, as Aservan mentions above.
Yes, it is the act of 'seeing' something, but its more the act of picking out that core detail.
A vigilant individual can see a dude looking sketchy in a crowd, and prepare for it. A perceptive individual realises the guy wasn't eyeballing the party, but the rich looking nobleman walking past them.
The difference between seeing action, and seeing detail.