[meindnoch]

>I’m pretty sure they mean perceptible complexity at the level of the human eye

That's precisely what they're wrong about.

Take a look at tree branches. A field of grass. A stone cliff.

Now take a look at human-made decor: drywall, plastic, laminated boards.

Which one has more visual detail?

[kulahan]

Our brains evolved in the former environment, and is very good at filtering it out. I've got pretty extreme ADHD, and if I'm in a room and something on the wall is flittering about, I absolutely must look at it. If I'm in a field and a tree is full of leaves billowing in the wind, it's a nice background thing. I guess my monkey brain is too busy looking for tiger faces to be distracted by flickering leaves, flowing grass, and flying bugs for more than a half second.

I dunno if I agree with their arguments in the paper (there seem to be some pretty big questions unanswered yet, which the authors acknowledge), but there's definitely something to the idea that natural environments aren't as stressful for us, even if they're objectively "busier".