James Angelini of the University of Delaware, Samuel Bradley of Texas Tech University and Sungkyoung Lee of Indiana University analyzed ads that aired during the 2000 presidential election.

For the study, the researchers placed electrodes under the eyes of willing participants and showed them a series of 30-second ads from George W. Bush, the Republican candidate for president in 2000, and Al Gore, the Democratic candidate.

The electrodes picked up on the "startle response" -- the automatic eye movement typically seen in response to snakes, spiders and other threats. Compared to positive or neutral messages, negative advertising prompted greater reflex reactions and a desire to move away, the researchers said.