How Can We See a Continuous Picture Being All Temporary Blind?

You cannot stare at a girl/boy or a painting, because your eyeballs move wildly to get shots of the various traits in the surrounding picture Eyeballs are known to stay still fixing on a spot for 0, 3 - 2 seconds; in between they shake around for up to 50 milliseconds, a moment when vision is stopped, installing a momentary blindness.

With all the crazy movement and temporary blindness, how can we see a complete and uninterrupted image of our environment? This could be the result of the "boundary extension": the brain builds scenes not only by received signals, but also by extrapolation.

In 1989 Helene Intraub, a psychologist at the University of Delaware, was the first to characterize boundary extension. When people looked at the same picture twice (like a bike in front of a white fence) within several milliseconds, they perceived the second image as a close-up of the first and not the same.

Curiously, when they saw the same picture and a wide-angle version (with the little smaller bike and more fence), they perceived the second photo as identical with the first.

"Basically, it appears that the brain is already planning around the edges, and this may be a way to help integrate successive eye fixations." said than Intraub.

Now, Intraub and psychologist Marvin Chun's lab at Yale University, employed functional magnetic resonance imaging (fMRI) to see what actually occurs in the brain. Two vision-linked brain regions were investigated: the parahippocampal area (PPA) and the retrosplenial cortex (RSC). The 18 subjects were presented four pairings of scenes, for the same view: a close-up then a wide-shot, a wide-angle then a close-up, a wide followed by a wide or two close-ups.

The RSC was turned on by the first flashed photo and by the second one, except the close-up followed by a wide-angle association. "The brain [region] is going, 'ho-hum, I've seen that before.'" explained Traub about this association.

PPA displayed a low activity in each case, except when a close-up followed a wide-shot.

"This pattern implies that the PPA experiences boundary extension, but also that it does pick up features in a scene, as well. In the PPA, what we found is if you show a close-up and then the same close-up again, there is still a recognition-it got a little attenuation." said Intraub.

The team also checked the lateral occipital cortex, where conscious images form.
In each situation, the second photo decreased its activity, thus it was just noting the presence of the central object (like the bike).

"We can't make any direct connection, because these regions are not involved in moving the eyes. Instead, this part of the brain is telling us about the mental representation," from pieces of information collected by the eyes.