Having a really good ability of viewing them, I feel like it relies on two separate skills :

- Fine voluntary control of your eyes' accommodation

- Ability for whatever system is creating your depth perception to be more "flexible", in the sense that it can more easily "lock" onto a depth perspective as well as switching between them.

Thinking about it now, I'm not even sure how much voluntary control people normally have over their eyes' accommodation, if not exposed to experiences that forces them to practice it. I can definitely remember a time where I was not able to focus my eyes at will, which makes me think that it's not something the majority of people can do (granted it was when I was a child, so it might just be something you learn with age).