The Art of Thinking Clearly: Better Thinking, Better Decisions

See also Hedonic Treadmill (ch. 46)

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70
WHY PROPAGANDA WORKS
Sleeper Effect
During World War II, every nation produced propaganda movies. These were
devised to fill the population, especially soldiers, with enthusiasm for their country
and, if necessary, to bolster them to lay down their lives. The U.S. spent so much
money on propaganda that the war department decided to find out whether the
expense was really worth it. A number of studies were carried out to investigate
how the movies affected regular soldiers. The result was disappointing: they did
not intensify the privates’ enthusiasm for war in the slightest.
Was it because they were poorly made? Hardly. Rather, the soldiers were
aware that the movies were propaganda, which discredited their message even
before they were rolling. Even if the movie argued a point reasonably or managed
to stir the audience, it didn’t matter; its content was deemed hollow from the outset
and dismissed.
Nine weeks later, something unexpected happened. The psychologists
measured the soldiers’ attitudes a second time. The result: whoever had seen the
movie expressed much more support for the war than those who had not viewed
it. Apparently, propaganda did work after all!
The scientists were baffled, especially since they knew that an argument’s
persuasiveness decreased over time. It has a half-life like a radioactive
substance. Surely you have experienced this yourself: let’s say you read an
article on the benefits of gene therapy. Immediately after reading it you are a
zealous convert, but after a few weeks, you don’t really remember why. More time
passes until, finally, only a tiny fraction of enthusiasm remains.
Amazingly, just the opposite is true for propaganda. If it strikes a chord with
someone, this influence will only increase over time. Why? Psychologist Carl
Hovland, who led the study for the war department, named this phenomenon the
sleeper effect
. To date, the best explanation is that, in our memories, the 
source
of
the argument fades faster than the argument. In other words, your brain quickly
forgets where the information came from (e.g. from the department of
propaganda). Meanwhile, the message itself (i.e., war is necessary and noble)

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fades only slowly or even endures. Therefore, any knowledge that stems from an
untrustworthy source gains credibility over time. The discrediting force melts
away faster than the message does.
In the U.S., elections increasingly revolve around nasty advertisements, in
which candidates seek to tarnish each another’s record or reputation. However,
by law, each political ad must disclose its sponsor at the end so that it is clearly
distinguishable as an electioneering message. However, countless studies show
that the 
sleeper effect
does its job here, too, especially among undecided voters.
The messenger fades from memory; the ugly accusations persevere.
I’ve often wondered why advertising works at all. Any logical person must
recognise ads for what they are, and suitably categorise and disqualify them. But
even you as a discerning and intelligent reader won’t always succeed at this. It’s
quite possible that, after a few weeks, you won’t remember if you picked up
certain information from a well-researched article or from a tacky advertorial.
How can you thwart the 
sleeper effect
? First, don’t accept any unsolicited
advice, even if it seems well meant. Doing so, you protect yourself to a certain
degree from manipulation. Second, avoid ad-contaminated sources like the
plague. How fortunate we are that books are (still) ad-free! Third, try to remember
the source of every argument you encounter. Whose opinions are these? And
why do they think that way? Probe the issue like an investigator would: 
cui bono
?
Who benefits? Admittedly, this is a lot of work and will slow down your decision-
making. But it will also refine it.