By Matt McGrath
Science reporter, BBC World Service
Voters' mind are made up long before they arrive at the ballot box
Scientists studying US voters say our political views may be an integral part of our physiological makeup.
Their research, published in the journal Science, indicates that people who are sensitive to fear or threat are likely to support a right wing agenda.
Those who perceived less danger in a series of images and sounds were more inclined to support liberal policies.
The authors believe their findings may help to explain why voters' minds are so hard to change.
In the study, conducted in Nebraska, 46 volunteers were first asked about their political views on issues ranging from foreign aid and the Iraq war to capital punishment and patriotism.
Those with strong opinions were invited to take part in the second part of the experiment, which involved recording their physiological responses to a series of images and sounds.
The images included pictures of a frightened man with a large spider on his face and an open wound with maggots in it. The subjects were also startled with loud noises on occasion.
By measuring the electrical conductance of the volunteers' skin and their blink responses, the scientists were able to work out the degree of fear they were experiencing - how sensitive they were to the images and sounds.
They found that subjects who were more easily startled tended to have political views that would be classified as more right wing, being more in favour of capital punishment and higher defence spending, but opposed to abortion rights.
The scientists explained that these political positions were protective of the volunteers' social groups.
"We focused primarily on things that we call 'protecting the social unit'," said John Hibbing from the University of Nebraska.
"So the idea is we have this unit - maybe it's the US - and we want to protect this from outsiders; so we might be opposed to immigration, we might advocate patriotism, and we like leaders who are strong and clear who are able to protect us from those outsiders.
"We might even be opposed to pornography or any kind of corrosive element that we see threatening the social unit.
"On the other hand, you have people who are more supportive of pacifism and who advocate gun control - and there are lots of areas where people who are less sensitive to threat would project those kinds of feelings into the political arena."
The researchers say there is no political relevance to their research - but Dr Hibbing feels it may help explain why it is so hard to change someone's mind in a political debate.
Different people, he said, started from a different psychological point.
"You have people who are experiencing the world, who are experiencing threat, differently.
"It's just that we have these very different physiological orientations. We're not sure where they came from, they may be genetic, they may be something from childhood; we do know, though, that they run deep because it's a reflex, it's not something you can change tomorrow, the depth of that may be something of an asset in figuring out why people are so stubborn in their political beliefs," he said.
"I even have the hope that this might facilitate understanding a little bit. Instead of political opponents thinking the opposite party are being wilfully bull-headed, you can say 'well ok, they see the world differently than I do'.
"People haven't just thought about things differently, they feel things differently."