Lynn Vavreck
Lynn Vavreck

Lynn Vavreck, a professor of political science at UCLA, is a co-author of “The Gamble,” about the 2012 presidential campaign. This column appeared in the New York Times.

Hillary Clinton’s campaign released an ad in late September called “Mirrors.” The ad shows young girls looking carefully at themselves in a mirror or on their mobile phones. A piano tune accompanies the images. Then a surprising thing happens. Donald J. Trump, in his own voice, says, “I’d look her right in that fat, ugly face of hers. … She’s a slob, she ate like a pig. … A person who is flat-chested is very hard to be a 10. … Did she have a good body? No.”

Both campaigns have used this viva voce style of advertising in this cycle. Maybe that’s no surprise, as it seems to be effective at moving voters.

In “Mirrors,” the images of teenage girls assessing themselves keep rolling by until the final frame poses a question — written, not spoken: Is this the president we want for our daughters?

“Mirrors” has aired more than 14,500 times since its debut, mostly in the battleground states of Florida and Ohio, but also on national cable networks like TRU TV, A&E and Bravo.

It’s a type of ad that the Clinton campaign has made more than once.

John G. Geer at Vanderbilt University and I have been gauging the effectiveness of this and other political ads by asking randomly assigned groups of people to react to and evaluate them all year. (The project is called SpotCheck, and you can watch all the ads we’ve tested and see how people rated them here.)

We’ve tested dozens of campaign ads aired by or on behalf of the two major party candidates since June. The viva voce ads stand out in a few ways. More people (57 percent) say these ads are memorable compared with Mrs. Clinton’s positive promotional ads (only 45 percent). Similarly, 54 percent of those randomly assigned to see ads like “Mirrors” and “Role Model” view them as truthful, while only 37 percent believe this about the promotional ads.

Fewer people say the ads using the candidates’ voices make them feel happy (21 percent vs. 49 percent) and hopeful (30 vs. 54) when compared with the promotional ads, and more say they make them feel angry and worried. Almost 75 percent of the people who saw an ad with Mr. Trump’s own words said the ad made them feel angry. Only 43 percent of those who saw one of Mrs. Clinton’s promotional ads felt this way.

Despite this recent use of the genre, ads that use only an opponent’s recorded audio for voice-overs are rare. The Clinton campaign has used Mr. Trump’s own words against him several times. A similar voice-over ad called “Role Models” ran during the conventions and showed images of children watching television as Mr. Trump is heard saying: “I love the old days. You know what they did to guys like that when they were in a place like this? They’d be carried out on a stretcher, folks.”

He goes on to make fun of a reporter with a physical disability and to denigrate Mexicans. “Our children are watching,” the tagline reads. More recently, Mrs. Clinton made another of these ads, called “America’s Bully,” in which Mr. Trump is compared to notorious movie bullies.

Attack ads generally make people less happy and hopeful, while making them more angry and worried, so perhaps the emotional response to the viva voce ads is to be expected. But Mrs. Clinton’s traditional attack ads were not rated as memorable or as truthful as the attacks using Mr. Trump’s voice. That approach seems to make the ad stick in people’s minds (of course, it could also have to do with the things he is saying).

The ads with Mr. Trump’s audio also moved people’s ratings of him more than the other ads. These ads raised the share of voters who rated him unfavorably by an average of five percentage points. That’s more than twice the effect of either Mrs. Clinton’s promotional or traditional attack ads.

Overall, Mrs. Clinton’s promotional ads did more to boost her own favorable ratings than these specialized attack ads, which makes them as effective as the viva voce attacks at influencing people.

What’s unusual about “Mirrors” and “Role Models” is how Mr. Trump supplies the entire spoken audio track. In 2012, the Obama campaign ran an attack like this against Mitt Romney, but instead of showing Mr. Romney speaking, it used his singing a version of “America the Beautiful,” which he did at many of his rallies.

The Trump campaign doesn’t have any ads quite like this running against Mrs. Clinton, though it did recently use her own voice against her in an ad called “Deplorables.” In it, Mrs. Clinton describes her concept of the “basket of deplorables” and the “half of Donald Trump supporters” who are in it: “the racists, sexist, homophobic, xenophobic, Islamophobic, you name it,” she is heard saying as the narrator of the ad returns to remind viewers that she is talking about “you, and you, and … you.”

“Deplorables” was a big hit when we tested it — mostly because it boosted the share of voters rating Mr. Trump as favorable by near double-digits, while also lowering the share rating Mrs. Clinton as favorable by two percentage points.

The effects are above and beyond whatever role partisanship is already playing in shaping these views and in many cases are particularly noticeable among independent voters. Love them or hate them, these attack ads using candidates’ words in their own voices — often in the absence of any other spoken audio — are proving effective at moving voters.