GRANADA, Spain (Reuters) - This student is in love. University of Granada psychology researchers can tell.
Not because she said so, nor by studying her body language. They just looked at thermographic images of her writing hand.
While staring at photos of their partner, 60 volunteers in new relationships put their dominant hand in freezing water for two minutes.
Thermal images of the hand taken before and after were then examined.
"There is a faster recovery of the hand. You can see the temperature here (on the side), so when you compare this image with the image that we have seen with (her looking at) friends this recovery is faster," said Mr Alex Moline, a researcher at the University of Granada.
Being in love increased the temperature of volunteers' cheeks, nose, forehead, and hands, by two deg C.
A control group who looked at photos of friends experienced no temperature change.
Mr Francisco Tornay, a professor of experimental psychology at the university, said, "The temperature is related to the state of the sympathetic or the parasympathetic nervous systems, and how you feel and how excited you are, and it's very sensitive and very simple to detect and measure the working of the peripheral nervous system."
Earlier research saw volunteers stripped to the waist having their temperature tested while telling lies. A "Pinocchio effect" showed that the temperature of people's noses changes when untruthful.
The team believes the technology could be integrated into cellphones.
"We think that if we really go on to analyse thermographical images in a more detailed way, pixel by pixel and frame by frame, in short videos we can use machine learning algorithms and we think we can detect or predict to some extent the emotional state of people just by taking a video of them," said Professor Tornay.
Next month the world's first thermal imaging phone, the Cat S60, goes on sale, aimed at tradespeople.
Future models might one day let you test anything from your loved ones' feelings to the truthfulness of your employees. It's enough to make some people's blood run cold.