Altered images: new research shows that what we see is distorted by what we expect to see

New research shows that humans 'see' the actions of others not quite as they really are, but slightly distorted by their expectations. 

Published in Proceedings of the Royal Society B, the study could explain why people get others’ actions so wrong and see ambiguous behaviour as meaningful, according to authors from the University of Plymouth School of Psychology.

The study, funded by the Economic and Social Research Council, saw 85 participants watch an actor reach for an object with a straight or arched trajectory on a touch screen. 

In each screening, the actor did one of four things:

  • Reached straight for target (efficient straight)
  • Reached straight for target with obstacle in the way – therefore expecting to be blocked by the obstacle (inefficient straight)
  • Reached over an obstacle with arched trajectory to get to target (efficient arched)
  • Used arched trajectory to get to target, even though there was no obstacle in the way (inefficient arched)
In the experiment, the hand movement action disappeared mid-trajectory and participants touched the last seen screen position of the hand.

Results (in this picture) showed that:

  • When the hand was moving with an arched trajectory with no obstacle in the way, people perceived that it was lower down (ie moving more efficiently) than it actually was
  • When the hand was moving in a straight trajectory with an obstacle in the way, people thought it was higher than when it travelled no obstacle in the way

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.


Study author Matthew Hudson said that 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.

“Primates interpret behaviour as goal-directed and expect others to achieve goals by the most efficient means possible,” he said. “While this is accepted among psychologists, little has been known about its underlying mechanisms. 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.

“So imagine you are a passenger in a car, and see a cat run out onto the street. If the driver has seen it, you can picture in your mind that they should now slow down and swerve to avoid it. If they don’t do this, you immediately know that they probably haven’t seen the cat and you can warn them. Such predictions can also be used to coordinate with other people. For example, if we want to do a joint task like catching a ball that someone throws to you, it helps if you already see, in your mind’s eye, what the other person is going to do.

“Finally, the results show that people 'see' others’ actions in the light of their own expectations. If you see someone look at something with a neutral expression and think they are angry, they might look a bit angrier than they really are. This might explain why people often get others’ actions so wrong and see ambiguous behaviour as meaningful.”

Co-author Katrina McDonough added:

“These findings are really helpful for our understanding of how we so effortlessly seem to directly ‘see’ the beliefs, intentions, and emotions drawn onto other people’s actions, and a possible next step to understanding how a deficit in this ability may contribute to the social difficulties encountered by those with autism and schizophrenia.”

The full study, entitled Perceptual teleology: expectations of action efficiency bias social perception, was written by Matthew Hudson, Katrina McDonough, Rhys Edwards, Rob Ellis and Dr Patric Bach from the University of Plymouth School of Psychology. It is available to view in the Proceedings of the Royal Society B (doi: 10.1098/rspb.2018.0638).


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