As the image in the video below gets bigger, whose face do you see? Marilyn Monroe's or Albert Einstein's?
Most people will identify the ghostly shot of Einstein, but if you see the face of a Hollywood pin up, you may need to make a trip to the optometrist.
The theory is that eyes with good vision will pick up the fine lines of Einstein's face and cause the brain to disregard Monroe's image.
The optical illusion was created by neuroscientists at Massachusetts Institute of Technology several years ago.
In a recent video by ASAPScience, the process behind the trick is explained.
Depending on how well you're able to focus or pick up contrast your eye will only see those details.
So up close, fine details such as Einstein's moustache and wrinkles are visible, but as the distance increases, or if your vision is poor, the ability to identify these things diminishes.
What you are left with is only being able to see general features, like the shape of a mouth, nose and outline of hair, in this instance, the face of Marilyn Munroe.
Dr Aude Oliva, who lead the group of neuroscientists that created "Marilyn Einstein", along with several other images, says the optical illusions not only reveal vision problems but can also show how the brain processes information.
In one study, participants were shown hybrid images for just 30 milliseconds, and only recognised the low spatial resolution, or blurred parts of the image.
But when the images were shown for longer, they only recognised the picture produced in fine detail, or in high spatial resolution.
Oliva says this shows that our brains discriminate what we see, picking out fine details in some situations and bolder details in others.