YORK, United Kingdom — People often say the mind can play tricks on us, but fascinating new findings by a team at the University of York suggests it’s actually the eyes that deceive the brain. Scientists have shown that the human visual system is indeed of capable of “tricking” the brain into making inaccurate assumptions about the size of nearby objects in the real world.

Study authors believe their work may hold implications regarding numerous aspects of everyday life. Examples include driving, how the justice system treats eyewitnesses in criminal trials, and security issues like drone sightings.

In collaboration with scientists from Aston University, the research team gave study participants photographs of full-scale railway scenes. Those pictures had both the upper and lower parts of the image blurred. Participants were also given photographs of small-scale models of railways that were not blurred. Next, everyone was asked to compare each image and determine which one was the “real” full-scale railway scene. Notably, the group perceived the blurred real trains to be smaller than the models.

“In order for us to determine the real size of objects that we see around us, our visual system needs to estimate the distance to the object,” says Dr. Daniel Baker, from the University of York’s Department of Psychology, in a media release. “To arrive at an understanding of absolute size it can take into account the parts of the image that are blurred out – a bit like the out-of-focus areas that a camera produces – which involves a bit of complicated mathematics to give the brain the knowledge of spatial scale.”

“This new study, however, shows that we can be fooled in our estimates of object size. Photographers take advantage of this using a technique called ‘tilt-shift miniaturization’, that can make life-size objects appear to be scale models.”

All in all, this work demonstrates that while the human visual system is no doubt highly flexible, at times capable of accurate perception of size by exploiting what is known as defocus blur, our eyes can also be subject to outside influencers that result in a failure to accurately perceive real-world object size.

“Our results indicate that human vision can exploit defocus blur to infer perceptual scale but that it does this crudely,” concludes Professor Tim Meese, from Aston University. “Overall, our findings provide new insights into the computational mechanisms used by the human brain in perceptual judgments about the relation between ourselves and the external world.”

The study is published in PLoS ONE.

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