Slow-Motion Video Makes People Look More Guilty, Study Shows

A series of studies showed watching videos in slow motion made viewers more likely to think the action was premeditated. Image Source/Getty Images
A series of studies showed watching videos in slow motion made viewers more likely to think the action was premeditated. Image Source/Getty Images

Imagine watching the 2016 Olympics: When shown in slow-motion, a tennis player wiping the sweat off her brow can look like a grand motion, and a gymnast's aerial move appears larger than life. Slowed video can make the boring seem exciting and the mundane seem extraordinary. But it turns out that slowing videos not only amps up the drama of a scene, but also creates bias in viewers — specifically when it comes to jury members in court cases.

Video footage of crimes often plays an important role in determining a perpetrator's punishment. In some trials, jurors may watch a slow-motion video of the criminal act in question, supposedly to better analyze the events that took place. But researchers, writing that "any benefits of video replay should be weighed against its potentially biasing effects," conducted a study that suggests slo-mo video doesn't always help jurors make well-informed decisions. Instead, the elongated time of the video makes it seem like the crime took longer to unfold, so jurors are more likely to perceive the action as intentional.


Whether a jury thinks a crime was premeditated can be the difference between a second- and first-degree murder charge, so it's a matter of life and death. This was the case in the 2009 murder trial of John Lewis, which the researchers used as the basis for the study. In the trial, the prosecution showed a slow-motion video of Lewis shooting a Philadelphia police officer, and the defense argued that the stretched time made the act seem premeditated. The prosecution rebutted by pointing out that the jurors saw the video at regular speed, too. 

To test whether slo-mo video actually increases perception of time and intent, the researchers conducted four studies.

Study one: Participants (acting as jurors) either saw the video of Lewis slowed down or at normal speed

Study two: Tested perceived intention in an NFL video of a prohibited helmet-to-helmet tackle, as well as the effect of video duration by pausing the video instead of slowing it

Study three: Tested whether displaying and mentioning video speed decreased bias

Study four: Required participants to watch the slo-mo, followed by the regular video 

Confirming the researchers' guess, showing slowed video quadrupled the odds that jurors would believe the shooter guilty of intentional murder before deliberation, assisted by the increased amount of time that jurors felt the defendant had to act. Also, viewers who watched the slow-motion tackle (the second study) were more likely to think it was premeditated — and pausing the video didn't change that. For the third study, even though viewers were repeatedly reminded it was a slow-motion video, that didn't change the results — they were the same as the first study.

And the final study showed that the viewers who saw only the slo-mo version of events were 3.4 times more likely to convict that viewers who only saw the regular version. Viewers who saw both speeds were 1.5 times more likely to convict. This demonstrates that showing both speeds lessens bias but doesn't completely eliminate it.

The authors admit that the study doesn't determine the effect of slowed video on the accuracy of viewers' judgment. But considering the fact that the Supreme Court of Pennsylvania ruled the slo-mo in Lewis' case admissible and that Lewis is on death row despite his appeals, the results of this study could change how we view the role of videos in determining criminals' sentences. And with the explosion of police body cameras, surveillance cameras and smartphone video, the effect of video replay speed on jurors could have even more importance in the coming years.