Did you see the seahorse? Chances are, even if you didn't see the image (hint: look at the black space this time), your brain still knew it was there.
According to research published in the journal Psychological Science, our brains pick up on images that we never consciously perceive.
Volunteers were shown a series of black-and-white images while hooked up to an EEG device that recorded their brain activity. Each image was shown for just under two-tenths of a second. Then the subject pressed a button to indicate if the object was something familiar (like a turtle or telephone) or novel (a random shape that they didn't recognize).
The task was simple enough, but there was one more layer that the subjects didn't know about: On the outside of some of the random shapes, a recognizable image was hidden in the background—like the seahorse silhouette in the picture above.
The team wanted to know what the brain does with images that are right in front our eyes but that we don't consciously see, like this seahorse. That's where the EEG testing comes in. About 400 milliseconds after subjects looked at the silhouette, a wave called a N400 was recorded by the EEG device, said lead researcher Jay Sanguinetti, a doctoral candidate at the University of Arizona. The appearance of that brainwave suggests that the brain is processing something meaningful.
So even though the majority of the subjects said they didn't notice the background images at all (some didn't believe they were there even when shown them after the study, notes Sanguinetti), their brains still produced the N400 wave.
If our brain recognizes that meaningful objects are right in front of us, why don't we notice them? "We think what's going on there is that potential objects in the visual scene—the novel white shape and the seahorses on the outside—enter into this competitive process, so they are literally competing for neural space in the brain," said Sanguinetti.
Whichever one wins that competition is the one you consciously perceive, and whichever one loses becomes part of the background. This process means we don't perceive everything that's out there; instead, our brains work to give us the best interpretation of the world.
"Intuitively, you think that when you look at the world you can really see it," said Sanguinetti, "but what vision research is starting to show is that what you are told to look for, and what you are doing, can really bias what you see."
And there may be ways in the future to make good use of those biases. An airplane pilot, for example, must look at a complicated dashboard while flying a plane. Perhaps the gauges could be redesigned, said Sanguinetti, to help the pilot's brain focus on critical information.
Would you have seen the hidden images? Test yourself by clicking though this selection of images from the study. Experiment participants saw each image for about two-tenths of a second, but you can take as long as you like. Find the answers in the caption for the final image.