M. Night Shyamalan is in the midst of a comeback. The writer-director of the blockbuster films Signs and The Sixth Sense has found new life in the world of low budget horror. “The biggest advantage of working with smaller budgets is that I have total creative freedom,” says Shyamalan. “There’s no financial pressure, compared to my previous films, and I can pursue ideas that might be considered offensive if I was making a one hundred million dollar film.”

Shyamalan’s last film, 2015’s The Visit, brought the writer-director his best reviews in more than a decade. The Visit was also a big commercial success, especially compared to its five million dollar production budget. Now Shyamalan has reteamed with The Visit’s producer, low budget maven Jason Blum, on Split, a psychological horror film inspired by Shyamalan’s long fascination with the concept of multiple personalities. “I’ve always been interested in how the brain works, and I’ve always been intrigued by DID [Dissociative identity disorder],” says Shyamalan. “I’ve always been fascinated with the elements of psychology and why we believe what we believe.”

In Split, James McAvoy plays Kevin, a man whose mind houses more than twenty different personalities, twenty-four to be exact. “It was a difficult role, and I needed an actor with an incredible skill set,” says Shyamalan. “I first met James when he was promoting the last X-Men film at the 2015 Comic-Con, and when I saw him he had approximately half an inch of hair on his head. This gave him an appearance that was easily adaptable to various characters, personalities. He looked like he could become anyone he wanted to, which was perfect, in terms of what I was looking for.”

In September, I had the chance to talk to Shyamalan by phone about the diverse cinematic influences and techniques he brought to Split, his long fascination with human psychology, and the surprising career shift he’s experienced in recent years.

DG: Where did the idea for Split come from?

M. Night Shyamalan: I’d had the idea for several years. I keep journals, which are filled with ideas for possible films, and one of those journals was full of ideas about split personality disorders. I’ve always been intrigued by DID, multiple personality disorder, and how the brain works. I’d say that my biggest genre influence was The Silence of the Lambs, which is one of my favorite films.

DG: Where do Kevin’s multiple personalities come from?

M. Night Shyamalan: Kevin’s childhood was full of abuse and trauma, and the different personalities entered him at different points in his life to help him cope with what was happening to him. Kevin, the real Kevin, is a very kind man. The personalities inside of him cover a wide range of emotions. Some of them are very entertaining, fun people, and some of them aren’t much fun to be around.

DG: Why did you pick James to play the role of Kevin?

M. Night Shyamalan: I knew this was a daunting role, and I knew that I needed an actor who possessed a vast range of skills. I needed an actor who could have a squeaky voice in one scene, be a woman in another scene. I needed someone who could change not only their voice throughout the film but also their physicality.

DG: How does Kevin’s physicality change in the film?

M. Night Shyamalan: DID patients have demonstrated an ability to change their body chemistry, change physically. It’s about believing you’re someone else, first of all, and then pretending that you have extraordinary abilities. For example, DID patients might believe that they possess great strength, which will make them lift heavy weights they ordinarily wouldn’t be able to lift. With Split, I wanted to explore what would happen if a DID patient like Kevin believed that they possessed supernatural powers. What would happen then? Is it possible? This was the foundation for the script.

DG: How would you describe Kevin’s relationship with his psychologist, Dr. Fletcher, played by Betty Buckley?

M. Night Shyamalan: She tries to help Kevin compact all of his personalities into one being. She’s done extensive research into DID, and she recognizes that Kevin is an extraordinary case. She believes that some DID patients can change their body chemistry, an idea that is dismissed by her colleagues. Different personalities visit her at different times. Some aren’t allowed to see Dr. Fletcher.

DG: Is there a supernatural explanation for what happens to Kevin in the film?

M. Night Shyamalan: Maybe. These patients with DID can change their body chemistry. They believe this. A patient who believes they’re a 250 pound weightlifter will exhibit incredible feats of strength, which defies belief. That’s what happens with DID patients. What if someone with DID thought they had supernatural powers? That’s the approach I took.

Split opens in theaters on January 20.