Click to enlarge. Source: YouGov

Deschanel with iPhone

FORTUNE — Some purists used the fact that Apple AAPL  had replaced the always appealing but generally anonymous faces in its TV ads with a couple of Hollywood celebrities — Zooey Deschanel and Samuel L. Jackson — as evidence that the company had gone to hell without Steve Jobs at the helm. (See Siri takes a star turn.)

But a new YouGov BrandIndex survey suggests that Apple marketing may still know how to do its job.

According to a report issued Tuesday, the Siri ads featuring Deschanel and Jackson coincided with a boost for the iPhone brand among the all-important demographic of 18–34 year old Americans:

“Just as the new Siri campaign premiered on April 19th, iPhone’s buzz score in the 18 – 34 demo was 16, several points below Android’s 26 score. Five days later, iPhone’s buzz score passed Android, 30 vs. 29… The iPhone’s buzz score peaked on May 4th with a 51 score, while Android moved a couple of points down to 27.”

Both men and women responded positively to the ads, according to YouGov, but men registered the strongest push.

YouGov BrandIndex’s Buzz score was determined, as usual, by asking respondents: “If you’ve heard anything about the brand in the last two weeks, through advertising, news or word of mouth, was it positive or negative?”

Brands tested included Apple, Google’s GOOG Android, BlackBerry RIMM , Motorola MOT , Nokia NOK , HTC and Samsung.