Researchers showed photos of men and women with one of six facial expressions – anger, fear, happiness, sadness, surprise, disgust – as well as a neutral look to 26 dogs at feeding time.
At the same time they monitored their heart rate.
The findings show just how much our four-legged friends relate to the emotions of their human owners.
If they think a human face is showing anger, fear or happiness they turn their heads to the left but if they recognise a look of surprise they turn their heads to the right.
The heart rate of dogs also goes up when they think their owner is unhappy, according to the study published in the specialist science journal Learning & Behaviour.
The pictures depicting anger, fear and happiness sparked the most cardiac activity – suggesting higher levels of stress.
The dogs also took longer to return to their food when these photos were shown to them.
Researcher Marcello Siniscalchi, of Italy’s Bari Aldo Moro university, said animals in the wild have to determine very quickly whether a situation is dangerous or not before deciding what action to take.
Though the test involved photos, the scientists believe voice, smell and body posture also act as clues for dogs to pick up on human emotions.
Dr Siniscalchi said: “Negative emotions seem to be processed by the right hemisphere of a dog’s brain and positive emotions by the left side.
“Our results support that of other studies done on dogs and other mammals. These show that the right side of the brain plays a more important part in regulating outflow of blood to the heart. This is a fundamental organ for the control of the ‘fight or flight’ behavioural response necessary for survival.”