Perception as Reception

We think perception is reception (of data from the outside world, or impressions), but tell me: How do we know this? Is their an introspective manner for us to establish this fact?
How much of what one perceives comes unsuspected? Not much, does it? Much of what we perceive conforms to our expectations.
How often is a perceiver startled? Not that often, I presume. Only incidentally are our expectations unsupported by reality.
If I am right, we need a theory of perception that explicates, explains this newly acquired insight.

Does it mean that our perceptions are projections of the perceiver and the world is not real? I don’t think so. But we should ask first how it is that we know that the world is real.