Take the mind-bending tests that reveal how our brain 'invents' part of our peripheral vision

Pick a focus point at the center of the images and hold your gaze to see the illusion. Photo / Uniformity Illusion

The world around you might not be exactly as it seems.

In a new study, researchers have found that some of what we see in the periphery - the areas just outside our eye's direct focus - could be a visual illusion.

A series of 'uniformity illusions' reveals this phenomenon at work, as our brain 'fills in' part of the scene to make up for our less accurate peripheral vision.

According to the study, published in the journal Psychological Science, peripheral vision captures far less detail than what's seen in the centre of the visual field.

But, in our day-to-day lives, we often don't notice a difference.

The researchers now say this could be the result of an illusion created by our visual processing system.

"Our findings show that, under the right circumstances, a large part of the periphery may become a visual illusion," says lead author Marte Otten, a psychology researcher from the University of Amsterdam.

"This effect seems to hold for many basic visual features, indicating that this 'filling in' is a general, and fundamental, perceptual mechanism."

In the study, 20 participants with a series of images and asked to focus on the center of the screen.

While the images start out with a distinct central image, the 'filling in' illusion causes them to eventually see a uniform scene as a different peripheral image fades in.

A number of these optical illusions are available for anyone to try on the Uniformity Illusion site.

Photo / Uniformity Illusion

"Perhaps our brain fills in what we see when the physical stimulus is not rich enough," Otten said.

"The brain represents peripheral vision with less detail, and these representations degrade faster than central vision.

"Therefore, we expected that peripheral vision should be very susceptible to illusory visual experiences, for many stimuli and large parts of the visual field."

The researchers also asked the participants to click the mouse as soon as they noticed that the difference between the central image and the periphery had disappeared.

They created a series of variations, altering the shape, orientation, luminance, shade, and motion of the central image.

And, this revealed that the uniformity illusion applied across the board.

Participants noted that they felt about as sure about their experience of uniformity when it actually existed as when it was illusory.

Photo / Uniformity Illusion

According to the researchers, this suggests these experiences are similar to those based on physical visual stimuli.

"The most surprising is that we found a new class of visual illusions with such a wide breadth, affecting many different types of stimuli and large parts of the visual field," Otten said.

"We hope to use this illusion as a tool to uncover why peripheral vision seems so rich and detailed, and more generally, to understand how the brain creates our visual perceptual experiences."