Acting is often rooted in details. For Paul Dano’s performance as a movie star named Jimmy Tree in “Youth,” so much depended on a pair of sunglasses.

“You kind of know those people who wear sunglasses all the time,” Dano says. “I could never sit here, if we were doing this in a hotel room, and wear sunglasses and do an interview. It’s something as simple as that: What would that be like?”

To get a feel for his character, Dano latched on to Jimmy’s shades — a detail included in the script by writer-director Paolo Sorrentino. Though Dano (“Love & Mercy”) and Jimmy share the same job, Dano says it’s not necessarily the case that they have anything in common.

“The attraction of the role was, what would it be like if I lived in Los Angeles and had sort of an early start in some ginormous film,” Dano says. (Jimmy is best known for playing a robot, to his clear chagrin.) “His struggle, to me, was [that of] somebody who doesn’t feel quite seen for who they are. He’s still another human being; I don’t think I was able to take any shortcuts in my own preparation just because he’s an actor and I’m an actor.”

Much of Jimmy’s time in “Youth” (opening wide Friday) is spent watching a variety of characters rotate around him at the luxurious Swiss resort where they’re all staying. Harvey Keitel plays a director working on his next movie, Michael Caine plays a retired composer on an extended vacation and Rachel Weisz plays the composer’s daughter, attempting to heal after the collapse of her marriage. Jimmy is preparing for a radically new role, and part of his work is studying the other guests’ behavior.

For Dano, Jimmy’s time spent in quiet observation was a huge bonus. “That was part of the gift of the role,” Dano says. “To watch Harvey and Michael and Rachel and Paolo … and not just study them on behalf of Jimmy, but to just be there and soak up the energy and the craft around me. As Jimmy, but also as Paul.”

More interviews from Kristen Page-Kirby