The world we experience isn't just given to us.
The brain is actively generating our experienced worlds every moment of every day.
If I'm sitting on the beach, and I open my eyes, I suddenly see before me the sea, the waves, I can feel the breeze on my face, I can hear the seagulls in the distance.
It seems like there's this objective world out there, and it's just pouring itself into my mind through the senses.
Yet, I know that's not what's going on.
The signals that arrive at our eyes and our ears, the light waves that hit our retinas, the pressure waves that come into our eardrums, they don't come with labels on them, like "I'm from a seagull", or "I'm from the sea", or "I'm blue".
They're just ambiguous signals.
The brain has to make sense of all these sensory signals and figure out where they came from and what they mean.
That's the process of perception.
So perception isn't just a reading out of the world around us, it's always a creative act of interpretation in which the brain is utilising its knowledge about the way the world is, to make its best guess of what causes the sensory signals, and that - that's what we consciously perceive.
