The Problem With Slow Motion in Watching Surveillance Footage of Crimes
Watching slow-motion footage of an event can certainly improve our judgment of what happened. But can it also impair judgment?
This question arose in the 2009 murder trial of a man named John Lewis, who killed a police officer during an armed robbery of a Dunkin’ Donuts in Philadelphia. Mr. Lewis pleaded guilty; the only question for the jury was whether the murder resulted from a “willful, deliberate and premeditated” intent to kill or — as Mr. Lewis argued — from a spontaneous, panicked reaction to seeing the officer enter the store unexpectedly.
The key piece of evidence was a surveillance video of the shooting, which the jury saw both in real time and in slow motion. The jury found that Mr. Lewis had acted with premeditation, and he was sentenced to death.
Mr. Lewis appealed the decision, arguing that the slow-motion video was prejudicial. Specifically, he claimed that watching the video in slow motion artificially stretched the relevant time period and created a “false impression of premeditation.” Did it?
We recently conducted a series of experiments whose results are strikingly consistent with that claim. Our studies, published this week in the Proceedings of the National Academy of Sciences, show that seeing replays of an action in slow motion leads viewers to believe that the actor had more time to think before acting than he actually did. The result is that slow motion makes actions seem more intentional, more premeditated.
In one of our studies, . . .
Read the whole thing. And it makes no difference if you tell the viewers the elapsed time, or if you also show the footage at normal speeds: the slow-motion view overrides everything.
It’s also an interesting example in which experience/evidence contradicts expectations, since the judge strongly felt that if the jurors knew the actual elapsed time and saw the regular video, the slow-motion video would not have an effect. As the experiments showed, the judge’s expectations were flat-out wrong.