'They can't stop now'

If the targets of this year's campaign ads are any guide, the presidential election will be decided by middle-aged and older white women, according to a survey of more than 1,000 buying agencies done by STRATA, a software firm whose systems help air some $50 billion worth of ads a year.

The question is whether the barrage of ads - the vast majority of them attacking a candidate, rather than promoting one - will become so overwhelming that they provoke a backlash.

Such ads "did work on me at first, and then I became a lot more cynical and realized that a lot of it is political warfare," said Harvey, who added that she voted for Obama in 2008 but was leaning toward Romney now. "It seems almost epidemic; they can't stop now that they've started."

A rule of thumb in advertising is that an ad needs to be viewed at least three times and up to 10 to be effective, said STRATA Chief Executive John Shelton.

"There's no question that once you start to go over (10), you start to, well, at least bore people," he said. "Then they might tune out. Then they might actually get ticked off."

Barbara Berry, a healthcare professional and Obama supporter from Columbus, said she pre-records TV programs and skips ads.

"I don't pay attention anymore," she said.

Since late August, more than 915,000 presidential campaign ads have aired on broadcast and national cable TV, according to the Wesleyan Media Project. In Columbus during October, ads by the campaigns and outside groups aired more than 7,000 times.

"Some of them just disappear in the noise," said Dan Bradley, general manager at the Columbus NBC affiliate WCMH-TV.

Each presidential campaign has been producing about a dozen new ads a week, basing them on daily news events - a practice that ensures that most of the ads have a short shelf life.

Romney in particular tends to place and replace ads at the spur of the moment, often in response to the news of the day.

Obama's campaign runs two ad tracks: one that changes every one or two days, the other every couple of weeks.

Ads this year "just seem to be rushed," said John Geer, a political ad researcher at Vanderbilt University. It's "almost like they've fallen prey to the fact that the campaigns have so much money, and the ability to make all these ads."