Humans perceive the actions of others not quite as they really are, but slightly distorted by their own expectations, a study has found.
The study, published in the journal Proceedings of the Royal Society B, could explain why people get others' actions so wrong and see ambiguous behaviour as meaningful.
Researchers from the University of Plymouth in the UK saw 85 participants watch an actor reach for an object with a straight or arched trajectory on a touch screen.
In some screenings of the actions, an obstruction was put in between the hand and the object it was reaching for.
The arched trajectory was therefore expected to avoid the obstruction, whereas the straight trajectory was 'inefficient' as it would knock into it.
Where there was no obstruction, the straight action was free to reach directly for the target, whereas the arched trajectory was unnecessary and unexpected.
In the experiment, the action disappeared mid-trajectory and participants touched the last seen screen position of the hand.
Results showed that people had judged that the straight trajectory hand moved higher if it was inefficient, to avoid the obstruction, while perceiving that the arched trajectory hand was further downwards towards the target if there was no obstruction.
In both cases, people's perceptions were based on what they had expected the hand to do to maximise efficiency — not what it actually did.
While the experiment pertained to physical movement, it might help us understand how people find out what others are thinking and feeling; in short, why they are behaving in the way they do, researchers said.
"Primates interpret behaviour as goal-directed and expect others to achieve goals by the most efficient means possible," said Matthew Hudson from University of Plymouth.
"While this is accepted among psychologists, little has been known about its underlying mechanisms," said Hudson.
"What we have found in this study may be important for various reasons. Firstly, it shows that people make predictions when they see the actions of others.
"It has been argued for a long while that people constantly make such predictions, and use them to figure out if other people see the same things as we do," Hudson said.