From pulling a trigger to swinging a fist, a lot can happen in a split second. And gauging what goes through the minds of those involved during such dramatic stretches of time can be incredibly difficult, if not impossible. That’s why law enforcement and prosecutors are increasingly using video. Not only do those digital plates depict fast-moving, life-changing events, they can also be slowed down so that the tiniest of movements can be dissected. This, the logic goes, doesn’t just clarify What happened, but helps explain what an alleged criminal is meant to happen. But according to a new study, slow motion could be blurring our vision.
Viewers who watch videos in slow motion — as opposed to normal speed — are more likely to feel that the people filmed are acting with deliberate, deliberate and premeditated intent, researchers report. The prolongation of events, it turns out, gives viewers the impression that people in video clips have more time to think and plan what they’re going to do. The findings, published this week in the Proceedings of the National Academy of Sciencessuggest that jurors viewing slow-motion footage of an alleged crime may place more responsibility on the accused than would otherwise have been the case.
“In legal proceedings, these letters of intent can mean the difference between life and death,” the authors conclude. “So all the benefits of video replay need to be weighed against the potential biasing effects.”
The authors, Eugene Caruso of the University of Chicago, Zachary Burns of the University of San Francisco, and Benjamin Converse of the University of Virginia, point to the 2009 murder trial of John Lewis. During the trial, prosecutors showed slow-motion surveillance video of Lewis fatally shooting a Philadelphia police officer during an armed robbery. The stretched footage was key to convincing the jury that the shooting was premeditated — counting as first-degree murder, which is punishable by death — rather than a reflexive first-degree murder with the possibility of life in prison. Lewis is currently on death row.
To see if artificially extended footage could change perceptions, the researchers showed 489 volunteers a similar five-second video clip of an armed robbery that ended with a robber shooting a sales associate. Participants watched the clip at normal or slow speed. Those who watched the delayed version were significantly more likely to believe the shooter intended to kill. When the researchers plugged their data into a simulation of 1,000 12-person juries, they estimated that if all 1,000 juries watched the regular speed video, 39 would return a unanimous guilty verdict. But if the juries looked at the slow-motion version, 150 of them would unanimously declare guilty.
These results held up in three additional experiments. In the second experiment, the researchers wanted to see if the extra time it takes to watch a slow-motion clip gave the audience more time to think about the events. Perhaps that extra time was the reason viewers changed their perception of intent. So the researchers got 580 volunteers to watch a video of a football tackle using a prohibited helmet-to-helmet hit. Viewers watched a slow motion version of the clip or a normal speed version with a single frame frozen. The frame was frozen long enough to equalize the duration of the two clips. Volunteers watching the slow-motion version were still more likely to believe the player was planning to knock helmets.
Then the researchers gathered another 410 volunteers to repeat the first experiment, but this time those watching the slow motion clip were repeatedly reminded that it was slow motion. Researchers wondered if verbal correction for the time distortion on the video would reverse the perception bias. Volunteers were instructed to watch the timestamp during the delayed clip and were told repeatedly how much actual time had elapsed in the clip. This did not change the results.
Finally, the researchers wondered whether viewing both the slow-speed and normal-speed versions of a clip — as is often the case with trials — would erase or lessen any bias that results from watching the slowed-down version. Another 905 volunteers watched a clip at normal, slow, or both speeds. Looking at both speeds, the researchers found, could reduce, but not eliminate, the bias.
“Current research cannot determine whether slow-motion replay makes viewers more or less accurate in judging premeditation in these situations,” the authors note. “But it does show that slow motion can systematically magnify the perception of premeditation itself.”
Proceedings of the National Academy of Sciences2016. DOI: 10.1073/pnas.1603865113 (About DOIs).