You don鈥檛 have to directly see an object to perceive it. Through a process called ghost imaging, patterned light shone on an object is used to recreate an image of the object without ever directly taking its picture. Understanding how our eyes can build up an image from simple checkerboard patterns of light could help us gain a deeper insight into the internal workings of the brain鈥檚 visual cortex.
Ghost imaging is an unusual way of taking a picture. Light in a series of different checkerboard-like patterns is bounced off an object and then collected in a 鈥渂ucket detector鈥� that simply records the brightness of the reflected light without collecting any information about the spatial dimensions of the object. When those same patterns are stacked together with their intensities set by the measurements of the bucket detector, they build an image of the object.
It鈥檚 like cooking from a recipe: the locations of the squares of light and darkness in the checkerboard-like patterns tell you the 鈥渋ngredients鈥� 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 cook up the final image.
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But 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 鈥� your eyes can cook up an image from the patterns with no additional help.
Ghostly Einstein
To demonstrate this, the researchers took the weighted patterns 鈥� all the ingredients in the right amounts 鈥� and projected them one after another听听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.
鈥淚f you project them extremely quickly, then the eye can鈥檛 follow these changes and everything just blurs together and your brain naturally integrates all the patterns in one,鈥� says Faccio. 鈥淎s you increase the speed, you went from seeing random patterns to all of a sudden this object emerging.鈥�
They found that the viewers integrate all of the patterns projected within a 20-millisecond-long window. Within that time window the researchers鈥� special projector could project 200 checkerboard patterns. If they slowed down the rate the projector jumps to the next pattern the picture of Einstein didn鈥檛 emerge.
Surprising eyes
鈥淭he eye can do a lot of surprising things involving putting different pieces of visual information together,鈥� says Rebecca Holmes at Los Alamos National Lab in New Mexico. 鈥淭his is similar to how the eye can combine movie frames to see a continuous image.鈥�
This may provide a new way to study how our eyes and brains integrate visual information, and how fast they do so, says David Irwin at the University of Illinois.
Integrating the patterns is just one part of ghost imaging, though. The human visual system can mix the ingredients if they鈥檙e already measured out, but figuring out whether it can do the measuring itself is the next step, Faccio says.
He says that this could potentially be accomplished by projecting the patterns in one eye all at the same brightness, and a simple light of varying brightness in the other eye to indicate the intensity of the patterns as dictated by the bucket detector.
鈥淚f it worked, what that would tell you is that the optical nerve system is actually able to cross-correlate the two signals from the two eyes,鈥� Faccio says. 鈥淚f we were to see a correlation of this kind, it would mean that there鈥檚 a lot more going on in the brain in terms of the visual system than we currently think.鈥�
arXiv
