A special region of the brain's visual cortex, which is in charge of distinguishing between background and foreground images, called V2, is what makes brain cells remember things, according to a new study.
Neuroscientists at The Johns Hopkins University have demonstrated that nerve cells in V2 can "grab onto" figure-ground information from visual images for several seconds, even after the images themselves are removed from our sight.
"Recent studies have hotly debated whether the visual system uses a buffer to store image information and if so, the duration of that storage. We found that the answer is 'yes,' the brain in fact stores the last image seen for up to two seconds," said Rudiger von der Heydt, a professor in Johns Hopkins' Zanvyl Krieger Mind-Brain Institute, and co-author on the paper.
He also explained that the image, which the brain grabs and holds onto momentarily is not detailed, and is more like a rough sketch of the layout of objects in the scene.
This may partly explain how the brain creates a stable visual world for us when the information coming in through our eyes changes at a rapid-fire pace-up to four times in a single second.
The study was based on recordings of activity in nerve cells in the V2 region of the brains of macaques, whose visual systems closely resemble that of humans.
Located at the very back of the brain, V2 is roughly the size of a wristwatch strap.
In the study, macaques were rewarded for watching a screen onto which various images were presented as the researchers recorded the animals' brain nerve cells' response.
Previous experiments have shown that the nerve cells in V2 code for elementary features such as pieces of contour and patches of colour. And V2 codes these features with reference to objects.
For instance, a vertical line is coded either as the contour of an object on the left or as a contour of an object on the right.
During the study, the researchers presented sequences of images consisting of a briefly flashed square followed by a vertical line, and then compared the nerve cells' responses to the line when it was preceded by a square on the left and when it was preceded by a square on the right.
The recordings revealed that the V2 cells remember the side on which the square had been presented, which means that the flashing square set up a representation in the brain that persisted even after the image of the square was extinguished.
Von der Heydt said that although the research is only a small piece of the "how people see and process images" puzzle, but it's very important.
The results of the study may eventually make it possible to understand the mechanism of this phenomenon and to identify factors that can enhance or reduce this important function.
It could further help researchers in unravelling the causes of - and perhaps even identifying treatment for - disorders such as attention deficit disorder and dyslexia.
The study has been published in a recent issue of the journal Neuron.