ATLANTA , Georgia ( CNN ) -- Terrorism , a slow economy and rising gas prices are issues that can keep American voters awake at night . Undecided voters gathered at Emory University , where Dr. Drew Westen studies how brains react to messages . Political strategists know that the most successful candidates are masters at capitalizing on fears such as these , and that can make a huge difference at the polls . In 1964 , Lyndon Johnson was running for president against conservative Barry Goldwater when his campaign unleashed the `` daisy ad . '' It showed a little girl counting as she plucked a daisy , charmingly mixing up her numbers . Then a baritone voice takes over , counting down to an overwhelming nuclear explosion . It 's followed with a warning that the stakes are too high not to vote for Johnson . The ad , which ran only once , was so chilling and effective , analysts say , it helped Johnson win the presidency by one of the widest margins in U.S. history . CNN recently gathered eight undecided voters to see how they would respond to attack ads and how the ads might affect their choices . They met at Emory University in Atlanta , Georgia , where psychologist Drew Westen studies how brains react to candidates ' messages . Westen , who wrote `` The Political Brain , '' said fear-based attack ads are effective because they tap into a voter 's subconscious . `` Those kinds of gut-level reactions tell us things like , ' I do n't feel like this person is telling us the truth , ' `` Westen said . `` Unless someone is a really good con man , those reactions are extremely helpful . The conscious brain processes only a tiny percent of information . '' Westen and his business partner , Joel Weinberger , have created software , through their company ThinkScan , that looks into a voter 's subconscious . The software does this by measuring people 's reaction time to certain words after they watch attack ads . The undecided voters in CNN 's group watched the ads and were then asked to identify the color of words such as `` weak , '' `` inexperienced '' and `` terrorist . '' If they hesitated , even for one-thousandth of a second , before they clicked on the color that corresponded with the word , Weinberger said , it meant the word had an impact . `` If the word is on their mind , if the word was activated , it will slow them down , '' Weinberger said . Westen predicted that the undecided voters would say they did n't like the ads and that the ads had no impact on them . He was right . The group watched Hillary Clinton 's `` 3 a.m. '' campaign ad , which was intended to make voters question Barack Obama 's experience . Viewers said that the ad was fear-mongering and that it did not make them think Clinton was a stronger leader than Obama . But the data , Westen said , showed that their brains reacted differently . Voters had the greatest hesitation with words like `` weak '' and `` lightweight '' during the color test . Westen said this meant the ad made them question Obama 's readiness . `` The purpose , too , is to make him seem scary , dangerous . 'You need to be afraid of this guy as president , ' `` Westen said . `` That message unconsciously got through . '' The undecided voters also watched an ad attacking John McCain for saying the U.S. could be in Iraq for the next 100 years . After watching the ad , the group gave it a thumbs-down . But researchers said the data showed that it left them feeling McCain has poor judgment and is too close to President Bush . The results were identical when the same test was given to a much larger group of 100 voters . This happens because the ads trigger a response in the part of the brain called the amygdala , which experiences emotions such as fear . When it is aroused , it overrides logic , according to Westen . Despite the ability of attack ads to affect voters ' subconscious thinking , Westen cautions that fear-based ads are risky because they can backfire . What advice does Westen have for presidential hopefuls ? `` They should make voters feel inspired by them and worried about their opponent at the same time , '' Westen said . `` It works . ''
Fear-based attack ads are sometimes used by candidates to influence voters . CNN gathered eight undecided voters to measure the impact of attack ads . Psychologist Drew Westen says fear-based ads appeal to voters ' subconscious .