The first thing that is particularly impressive about this optical illusion is definitely its name!

The so-called «Thatcher effect» is nothing more than an incredible optical illusion that was given the name of the “Iron Lady” just because the photo of the British Prime Minister was used to create it over 30 years ago.

The second thing that comes as a surprise is that at first glance, nothing seems strange in the vertically flipped picture.

But as soon as you see it the opposite way, it turns out that the depicted face was… upside down all this time! Once the photo returns to the right place, the mystery is solved and the effect is revealed! But how is this possible?

It is very difficult for the viewer to identify specific changes in the characteristics of an inverted face (eyes, nose, eyelids, etc.), although these changes are evident in the “normal” face. Therefore, the Thatcher effect comes down to the following:

The image in the normal position has overturned eyes, nose, mouth, or eyelids, which can be clearly seen.

However, once the same image is turned upside down, the alterations in the characteristics disappear as if by magic, i.e. the viewer sees a normal image turned upside down!

Thatcher effect illusion
Photography: Rob BogaertsImage manipulation: Phonebox, CC0, via Wikimedia Commons

For some reason, the brain just skips the inverted characteristics when the face is upside down. Studies show that this phenomenon may occur due to the processes involved in face recognition and the perception of facial expressions that take place in the human brain.

“Our results demonstrate clear evidence for orientation-dependent sensitivity to changes in facial expression is a key component of the neural network underlying face perception”, write researchers.

Moreover, scientists didn’t stop just here and experimented with rhesus monkeys and chimpanzees to find out whether they perceive this optical illusion too.

Experiments showed that they do indeed experience the Thatcher effect, which means that it probably has evolutionary roots. Scientists believe that this glitch in facial perception may have emerged in a common human ancestor over 30 million years ago.


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