In the 1940s during WWII, the US Department of War wanted to know if their propaganda films were really working. So they carried out a series of experimental studies into how they affected soldier’s attitudes.
The complacent assumption was that the films should easily influence the average GI. Producers and psychologists alike expected to see a huge shift in attitudes towards the war after they were viewed. What they found was nothing of the sort and the results came as a bitter blow to propagandists everywhere.
While the films were informative and did strengthen some existing attitudes, experiments showed they were extremely unlikely to make soldiers more optimistic about the war in general (Hovland et al, 1949).
In retrospect this should have come as little surprise since the soldiers knew these were propaganda films designed to change their attitudes, so their defenses were up.
What they did discover, though, was that some of the films did have an effect on soldiers after months had passed. While attitudes didn’t change immediately, subtle shifts were picked up nine weeks later. US soldiers who watched one film about The Battle of Britain showed little extra sympathy towards the British five days later, but, after nine weeks, they had softened. Yale University’s Carl Hovland and colleagues called this the ‘sleeper effect’.
Since then the sleeper effect has had a rockier history than the average soap opera character. It has gone up and down in the esteem of psychologists over the years as some experiments have confirmed the effect and others have found nothing.
Quite naturally many people wondered whether the sleeper effect really exists, especially as it goes against common sense. Persuasion should really be strongest just after a message is delivered. Over time the persuasive effect should weaken as people’s attitudes return to how they were before—and this is what many other studies have shown.
Nevertheless when researchers have weighed up all these studies, it seems likely the effect does exist (Kumkale & Albarracin, 2004). It’s just it only appears under two circumstances:
- Big initial impact: the sleeper effect only emerges if the persuasive message has a major initial impact. If it isn’t powerful enough, it won’t hunker down in our minds, biding its time before it boomerangs back.
- Message discounting: it should be obvious that the source of the message can’t be trusted so that we discredit it; like when the soldiers were watching the propaganda film.
What seems to be going on is this: people are convinced by the arguments until they see that the source of the message can’t be trusted. But people don’t tend to process the discounting cue very thoroughly. So, over time, people forget they discounted the information and the content of the persuasive message, which was processed thoroughly, does its devilish work.
Know the source before the message
The sleeper effect isn’t the great news for advertisers (and advertising agencies) you might imagine. The effect is strongest when the message is discounted afterwards. When we watch adverts, we usually know beforehand that they can’t be trusted, so our minds are already on alert for the distinctive smell of half-truths.
There are all kinds of everyday situations where the sleeper effect occurs. Like when the travel supplement recommends a great resort, then we read at the bottom the trip’s cost was covered by the resort. Or there’s an article telling us about the health benefits of milk and then we read at the bottom that the author is the head of the Milk Marketing Board. Any time we receive a persuasive message before we find out who the source is, the sleeper effect can come into play.
Naturally, then, canny information consumers will want to know the source of a message before they read it.
About the author
Psychologist, Jeremy Dean, PhD is the founder and author of PsyBlog. He holds a doctorate in psychology from University College London and two other advanced degrees in psychology.
He has been writing about scientific research on PsyBlog since 2004. He is also the author of the book “Making Habits, Breaking Habits” (Da Capo, 2003) and several ebooks:
- Accept Yourself: How to feel a profound sense of warmth and self-compassion
- The Anxiety Plan: 42 Strategies For Worry, Phobias, OCD and Panic
- Spark: 17 Steps That Will Boost Your Motivation For Anything
- Activate: How To Find Joy Again By Changing What You Do
Image credit: Thomas Lieser
Psychology of Persuasion
→ This post is part of a series on persuasion techniques:
- How to Influence People
- The Persuasive Power of Swearing
- Loudest Voice = Majority Opinion
- Don’t Take No For An Answer
- The Influence of Fleeting Attraction
- Caffeine Makes Us Easier to Persuade
- Persuasion: The Right-Ear Advantage
- Balanced Arguments Are More Persuasive
- The Battle Between Thoughts and Emotions in Persuasion
- Are Fast Talkers More Persuasive?
- Persuasion: The Sleeper Effect
- Communicating Persuasively: Email or Face-to-Face?
- The Influence of Positive Framing
- The Illusion of Truth
- 9 Propaganda Techniques in Michael Moore’s Fahrenheit 9/11
- Persuasion: The Third-Person Effect
- 20 Simple Steps to the Perfect Persuasive Message
- Why Stories Sell: Transportation Leads to Persuasion
- How To Encourage People To Change Their Own Minds
- When Does Reverse Psychology Work?
- The One (Really Easy) Persuasion Technique Everyone Should Know
- The Single Most Effective Method for Influencing People Fast
- 9 Ways The Mind Resists Persuasion and How To Sustain or Overcome Them
- How To Make Persuasive Eye Contact