Our Eyes Can See Images that Don’t Exist

Some people in the ancient times had given us some words about perceiving, and they said seeing is not believing. You don’t have to directly see an object to perceive it. Computers can recreate an image of an object just from a series of chequerboard-like patterns of light shone on it – without ever directly taking its picture. Now it seems that our eyes can do the same.

Understanding how our eyes build up an image from the simple patterns of light could help us gain a deeper insight into the brain’s visual cortex. “Ghost Imaging” is an unusual way of creating a picture. Light in a series of different chequerboard-like patterns is bounced off an object and then collected in a “bucket detector” that simply records the total brightness of the reflected light without collecting any information about the spatial dimensions of the object.

When the patterns are stacked with their intensities set by the measurements of the bucket detector, they build an image of the object. It’s like cooking from a recipe; the locations of the squres of light and darkness in the chequerboard-like patterns tell you the “ingredients” of the object being imaged, and the intensity measurements tell you how much of each ingredient needs to be added. Then, a computer mixes the right amount of each pattern, following the recipe to create the final image.

However, Daniele Faccio at the University of Glasgow in the UK and his colleagues have now found that at least for part of the process a computer may not be necessary – your eyes can create an image from the patterns with no additional help. To demonstrate this, the researchers took the weighted patterns – all the ingredients in the right amounts – and projected them one after another on a screen. They then increased the speed that the patterns flipped from one to the next until five volunteer viewers said that they could see the intended image, a photo of Albert Einstein (arxiv.org/abs/1808.05137).

This may provide a new way to study how our eyes and brains integrate visual information, and how fast they do so.