The Presidential Debate: Will Body Language Contribute to Who Wins or Loses?

"But it's hard to make a prediction because tonight's format will be the first time it's ever been tried," Schroeder said.

What's different about this debate at the University of Mississippi in Oxford is that McCain and Obama will have five minutes to engage each other after answering each question posed by moderator Jim Lehrer of PBS.

"We don't have any historical guides to how candidates behave. It does mean how they treat each other becomes more important," Schroeder said.

McCain, the Republican nominee from Arizona, and Obama, the Democratic nominee from Illinois, will square off beginning at 9 p.m. for 90 minutes of verbal sparring on foreign policy and national security. Each will have a maximum of two minutes to respond to Lehrer's queries. The debate will be broadcast live on most major networks.

"Interactive actions could be uniquely important," said Gordon R. Mitchell, a University of Pittsburgh professor who focuses on the theory of argumentation and directs the William Pitt Debating Union. "With a five-minute free-for-all open discussion, repeated for 90 minutes, it's really going to be dramatic."

A possible Obama strategy could be purposely interrupting McCain to provoke his temper, Mitchell said. McCain, on the other hand, could bait Obama into appearing elitist with Reaganesque quips that diminish Obama's oratorical flair.

During a 1980 presidential debate, Ronald Reagan won favor by shaking his head and responding, "There you go again," to a point made by Jimmy Carter about Reagan's stance on Medicare.

But the ways candidates move mean much more than simply impressing the electorate during a debate, said Karen Kohn Bradley, a public-speaking coach and dance professor at the University of Maryland. She has studied politicians' body language since 2002.

"Those behaviors reveal their attitudes toward making decisions, how well they work with others, if they're solitary or independent thinkers or if they consult others," Bradley said.

She wonders what style each candidate will adopt during the debate. Bradley said both nominees recently have changed their physical demeanors -- which, depending on voters' preferences, could be viewed as positive or negative.

McCain, for example, conveyed himself as a highly stable candidate throughout the primary season by doing things such as taking a wide, grounded stance and gripping the sides of the podium.

"Now, he's gotten into swaying in the wind a little bit and looking around, which makes him look more equivocal," she said. "I don't know if this is making his supporters nervous or not. Voters drawn to him for his solidness might be concerned."

Until recently, Obama "wandered" while on a dais and "stared off into distances" while other people spoke.

"Some people interpreted that as attuning and listening to those around him," Bradley said. "Others saw it as he doesn't have a position. Well, we've seen that change. Now, he takes a stand. That could make his supporters very nervous. Now that they know where he stands and they may not agree with him."

The most crucial strategy is to radiate confidence, calm and strength, said David Lanoue, an expert on presidential debates who chairs the political science department at the University of Alabama.

"Do the things your mother always told you to do," Lanoue said. "Be as natural as possible. Stand up straight. Look at the people you're talking to -- in this case, the American people.