What you see reveals where you come from

In an experiment conducted by researchers from Harvard University and the London School of Economics, 81 percent of viewers from the USA and the UK stated that they only saw rectangles in this so-called coffer illusion, while 48 percent of people from Namibian villages only saw circles - and only under two percent only saw rectangles. None of the participants from the USA and the UK saw only circles.

The study suggests that the environment in which people grow up or live plays a role in perception - in other words, that people who live surrounded by rectangular architecture also recognize these shapes more easily. The traditional villages of the indigenous Himba people in Namibia tend to have round huts rather than dwellings. This also explains the response of a participant from there, who perceived circles but at the same time replied that she recognized "houses" in the picture.

The researchers recorded the changing perception by asking the test subjects after the first answer whether they recognized any other shapes in the picture. In the group from the USA and the UK, around 17 percent first saw rectangles and then circles. 3 percent saw circles first, then rectangles. 48 percent of the Namibians stated that they saw circles first and then the rectangles, while the rest saw rectangles first and then circles (less than three percent).

The answers of a third test group support the hypothesis of the analysis, which has not yet been published in a specialist journal, but as a so-called pre-print study online: Participants from Namibia, who did not live in the countryside but in an urban environment with more rectangular structures, had a more mixed perception: 19 percent saw only circles, 67 percent saw circles first, then rectangles, and as many as 13 percent saw rectangles first, then circles.

Visual perception differs between population groups

According to the study, visual perception is generally regarded as a mechanism that is the same for all population groups. This assumption is so strong that science has not even bothered to investigate cultural effects on perception.

The research team sees its findings as important evidence that cultural experiences do play an important role in human perception. "This shows how important diversity is," the psychologist involved, Michael Muthukrishna from the London School of Economics, is quoted as saying in an article in the journal "Science". "If you're trying to get a complete picture of the world, you should have some people in the room who see circles, while you only see rectangles."