In January of 2008, Peter Paton and two other actors from the Midcoast went to Boston University for an open casting call for a film adaptation of Dennis Lehane’s 2004 thriller “Shutter Island,” to be directed by Martin Scorsese.

There were 3,000 people there, by Paton’s count. He and his friends dropped off headshots and resumes and had their picture taken by the auditioners and went home.

Of the three who went to Boston, only Paton got a call back.

Paton, 60-something and gnomish in stature, with wide-set eyes and an intent, slightly cockeyed gaze, has a look that says character actor. He has been cast as a gravedigger and a butcher shop worker, and numerous times under the catchall descriptor “old man.”

In conversation, he notes that directors often like actors that look nondescript, because their appearance can be shaped to the role. “I don’t have that look,” he said.

His role in “Shutter Island,” a walk-on part with no lines, required spending seven days of shooting, off and on, in the summer of 2008. The location was the 115-year-old Medfield State Hospital, a mental hospital in Medfield, Mass. that shut its doors in 2001.

To fit the period of the film, which takes place in the mid-1950s, the hospital was dressed as a working facility and given the name Ashecliffe Mental Hospital from Lahane’s novel.

Paton was among a group of extras cast as hospital patients, or inmates as they would have been regarded at the time. Paton said an underlying theme of the film is the difference between treatments of the mentally ill, then and now.

Hospitalization for mental illness peaked in the United States in the 1950s. Lobotomies were the go-to treatment for schizophrenia, and electroshock therapy was common for a variety of conditions. Patients often spent their days sedated. The image of a mental hospital in which berobed patients wander aimlessly, mindlessly, through echoing, tiled corridors dates to these post-war hospitals.

As such, Paton appears in several scenes, maybe sedated or lobotomized, always in the background, never for more than a moment or two.

On his first day of shooting Paton was stationed in a room that he described as half the size of the space where he was sitting when he made the comparison — the Belfast Co-op. For the scene, he sat at a table playing Solitaire, while the principals acted in the foreground. “I have to admit, I was a little starstruck that day, being in a room that size with [Leonardo] DiCaprio, Scorsese and Ben Kingsley,” he said. Whether Paton appears in the final cut is hard to tell.

The shots of the room as Ben Kingsley’s character describes the disappearance of a patient to DiCaprio’s U.S. Marshal’s character are quick, incidental. The only line from an extra comes when the camera jumps away from the dialogue just long enough for a trembling, middle-aged man in a robe to moan the nonsequitur, “Why?”

Over the course of the week, Paton watched Scorsese and company in action and became less star struck, more respectful of the cast and crew’s dedication to the project. Of Scorsese, DiCaprio, Kingsley, and Mark Ruffalo, who plays DiCaprio’s partner in investigation, Paton said, “They’re all hard workers. It’s very intense. It takes a lot of patience on the part of everyone.”

Paton claims to have never acted before he was 50. He began with parts in Belfast Maskers productions and has gone on to log credits in 30 stage productions and 100 student films, the latter mostly through Maine Media Workshops in Rockport. “Seeing as how the cast is very young down there [in Rockport], I often get cast as … old guy,” he said with a chuckle.

For most of his life, Paton was a farmer. As he describes it, he was born into farming, first in western Massachusetts, and later in Troy where his family bought a 700-acre farm in the 1950s. Paton worked that piece of land until he and his wife split several years ago. He still lives on a portion of the land but no longer farms.

“Now I’m working at Hannaford,” he said. “Trying to become a legend.”

Beyond his stage credits, Paton has appeared in programs aired on the History Channel, including a piece about Bucksport founder Jonathan Buck, and one about the Salem witch trials. His image appears in a family photograph in the film adaptation of Richard Russo’s novel “Empire Falls.”

Beyond acting, Paton has written a number of his own productions. The latest of these, a variety act called “The Peter Paton Show,” is slated to run in June at the Unity Centre for the Performing Arts.

Paton’s longest exposure in “Shutter Island” — though still brief enough to pass during the time it takes to see how much popcorn is left in the bag — comes in the closing moments of the film. The scene is set outside the mental hospital. He and a half-dozen other inmates are being kept busy trimming shrubs and raking the front lawn, while DiCaprio shares a cigarette with Ruffalo on the steps of the hospital.

“I spent several days trimming the same hedge,” Paton said. “I probably pretty much killed it.” The hedge was rented for the film, as was the lawn, to make the hospital look as it might have in the years after World War II.

When Shutter Island opened at the Colonial Theatre in Belfast, owner Mike Hurley invited Paton to appear as a guest of honor. His admission was free and he gave a short talk before the show.

Paton had planned to engage the stopwatch function on his cell phone when the film started but decided it would be in poor taste to be using a cell phone during a movie. Given the scale of the film and the renown of the director and cast, Paton could be forgiven for wanting to note the exact time of his association with those forces — his brush with the zeitgeist. But as a writer and actor, what he really wanted was to study the development of the story on-screen.

“I wanted to time when things happen,” he said. “Most films do follow the same pattern.”

Paton elaborated. At the beginning of a film, the director has a certain number of minutes to include all factions. Typically, at the halfway point, he said, something significant happens. And near the end, some sort of stumbling block presents itself. “It’s pretty standard in films,” he said, with the exception to art house films, which he described as more likely to disregard the rules.

Paton liked “Shutter Island” and he hasn’t been entirely alone. The film opened at No. 1 at the box office, and has achieved a fair amount of buzz based on a late plot twist.

“It was cast well,” Paton said, reflecting on the marquee names. Paton is soft spoken and his sense of humor is dry enough that the subtle jests he drops could easily go unnoticed. “I did my part well,” he said with the slightest hint of irony.

Since the “Shutter Island” shoot, there have been fewer casting calls for blockbuster films, a trend that Paton chalks up to the economic downturn. But he has had some work.

Last October, he went to Cambridge for a scene in a film starring Ben Affleck. “A bunch of us are milling around on the street,” he said. “He [Affleck] and a few others are robbing a bank.”