We are working on brain and perception at this time. My question is regarding the Gestalt theory.

Why is it some people who look at a 3 dimensional optical illusion, CAN easily distinguish the “decided” pattern(s)?
And

Why is it some people who look at an optical illusion, CANNOT distinguish the “decided” pattern(s)?

What part of the brain is affected?

Is there anything else that is different between these people?