HOLLYWOOD, California—As filmmaking technology has advanced, films have changed to take advantage of it. The 2005 version of King Kong looks and feels nothing like the 1933 version. The newer Kong appears in vivid color, and thanks to CGI he’s a convincingly lifelike beast. The original soundtrack is tinny and shrill; in the newer one, the great ape’s snorts and growls are deep and realistic.

Movies have changed in less obvious ways too, says James Cutting, a psychologist at Cornell University who’s been studying the evolution of cinema. Cutting presented some of his findings at a recent event here sponsored by the Academy of Motion Picture Arts and Sciences. “All these things are working to hold our attention better,” Cutting said.

Here are a few of the most important ways in which movies have changed in the past century, according to Cutting.

Shorter shots

The average shot length of English language films has declined from about 12 seconds in 1930 to about 2.5 seconds today, Cutting said. At the Academy event he showed a scatter plot with data from the British film scholar Barry Salt, who’s calculated the average shot duration in more than 15,000 movies made between 1910 and 2010. That's a lot of shots. In a 2010 study, Cutting found an average of 1,132 shots per film in a smaller sample of 150 movies made between 1935 and 2010; the King Kong remake, incidentally, had the most: A whopping 3,099 shots packed into 187 minutes.

The average shot length in English language films has been declining, according to research by James Cutting. The graph in top right shows the same trend reflected in a larger dataset compiled by the British film scholar Barry Salt. James Cutting

Cutting says some people have tried to pin declining shot lengths on MTV, by invoking a sort of video-killed-the-attention-span hypothesis. He doesn’t buy it. For one thing, Salt’s graph of declining shot durations has no obvious inflection point in or after 1982, the year MTV was born. Shot durations were declining before that, and they kept declining at a similar rate after.

Cutting isn’t sure what's driving the change. One factor could be that older films tended to pack more characters into a shot. As a result, film makers had to allow more time for viewers to look around to see who was there. In one recent study Cutting found that each additional character added 1.5 seconds to the length of a shot on average.

Different patterns of shots

A short attention span is part of the human condition, Cutting says. The American psychologist William James knew this more than a century ago. "There is no such thing as voluntary attention sustained for more than a few seconds at a time,” James wrote in 1890.

What that means, Cutting says, is that no matter how hard we try to focus, our attention has a natural tendency to waver. “People flake out every few seconds,” he said. “You fluctuate in and out, and there’s a natural pattern to this.”

In a 2010 paper, Cutting argued that the pattern of shot durations over the course of a movie has changed over the years in a way that makes movies mesh better with the natural fluctuations in human attention. Every new shot requires the viewer to re-orient their attention, Cutting says. A movie with only short takes would demand too much of viewers’ attention. A movie with only long cuts might cause people’s minds to wander. The right mix makes it more likely that an audience will stay engaged and lose themselves in the movie, Cutting says. (The Empire Strikes Back, for example, accomplished this with its rhythm of short-take action sequences separated by periods of relative calm). Not everyone agrees with Cutting's analysis, and the paper has provoked a lively discussion among film scholars.

Film noir is an example of an older style that doesn’t match well with natural fluctuations in human attention, Cutting says. Many of these movies were made on a low budget in the 40s and 50s, and the filmmakers relied more on long takes. Modern filmmakers have more footage to work with, including archival video and other stock footage, allowing them to put a movie together in more different ways. Cutting thinks this could be one reason for the shift: Modern movies may mesh better with natural fluctuations in attention simply because it’s gotten easier to create movies that do this.

More motion

It probably comes as no surprise, but modern movies have more action than older films. Cutting has quantified this trend by calculating how many pixels change from one frame to the next across the entire movie.

This change also helps maintain viewers’ attention, Cutting says. “Our response to motion is physiological,” he said. When people watch action sequences their heart rate increases, and so does their galvanic skin response, an indicator of physiological arousal. Tying the motion to shot changes is an especially effective way to engage the attention of viewers, he says.

But filmmakers risk irritating audiences if they bombard them with frenetic motion for too long. The graph below shows what Cutting calls the "triangle of tolerability,” a sweet spot (shown in grey) where the shot duration and amount of motion are well suited to keep viewers’ attention. The black dots in the lower right corner represent the average shot length and motion index for entire films. The white and gray dots to the left represent sequences, and fragments of sequences from within movies. The point is that when film makers use lots of motion, they usually only keep it up for short periods of time.

Too much motion for too long can make movie audiences queasy. James Cutting

Audiences sometimes revolt against movies that buck this trend. For example, the incessant, jerky handheld camera work in the 2008 film Cloverfield nauseated some people. Cloverfield/em> sequences are represented by the c’s on Cutting's graph, above the triangle. The graph includes two other movies that were criticized for too much queasy cam: Quantum of Solace (a), and The Bourne Ultimatum (b).

Director Darren Aronofsky was on stage with Cutting as he presented this work, and Cutting highlighted two sequences from Aronofsky’s films: an intense and hallucinatory night club scene from Black Swan, and the sequence from Noah that depicts the entire history of human violence in about 10 seconds. Both fall inside Cutting’s triangle of tolerability, but just barely.

“If you go into madness with the camera choices it just becomes chaos that doesn’t represent what the characters are feeling,” Aronofsky said. “For me it’s about trying to capture where the character is and to try to give that subjective experience to the audience.”

For the nightclub sequence, Aronofsky worked with a Photoshop artist who manipulated each frame and added some subliminal imagery. He seemed slightly disappointed that the sequence fell within Cutting’s triangle of tolerability. “I actually wish that had gone over the edge,” he said. "I’m a little disturbed we didn’t push that far enough.”

Changing light

Modern movies are also darker than their predecessors, Cutting has found. “What’s happening is that the brights are staying just as bright, but the darks are getting darker,” he said. "The quality of the film stock has gotten better. The move into digital has given us better control over the dynamic range.”

As an example, he showed a still from Harry Potter and the Deathly Hallows: Part 1 in which a menacing Lord Voldemort looks like he's just about to unleash some wickedness. The frame is almost entirely black, except for a glow at the tip of his wand that lights up his face and hands. It’s one way film makers control where the audience looks and what they see, Cutting said. “When you make the darks dark, you remove the possibility that people will look at them."

Cutting is also investigating the use of color in films, using a Matlab script to analyze the palette of colors in movies frame by frame. So far he's found some interesting uses of color in individual movies, such as different color schemes corresponding to different dream levels in Inception (see image below). But he says it's not yet clear whether there are any consistent trends in movie color schemes over the decades since color was introduced.

This story is part of a series about how scientists are studying cinema for clues about the nature of perception, and how the science might aid film makers as they pursue their art.