We blink about 25 times a minute, causing a profound disruption in our visual input each time. However, the interruption usually goes unnoticed because higher processing systems temporarily suppress the visual pathway, according to a report in the July 26 issue of Current Biology.
Scientists have thought such a suppression mechanism existed but did not know how it worked. To decipher between suppression and an actual reduction in visual signals because the eyes are momentarily closed, Davina Bristow and colleagues of University College London shined a light through the roof of a volunteer’s mouth, so that the retina detected the same amount of light regardless of whether the volunteer was blinking. (The volunteers wore opaque goggles so their pupils detected no additional light.)
Then, using a functional magnetic resonance imaging scanner, the team looked to see what areas in the brain were active before, during, and after a blink in each of eight volunteers.
During blinks, neural activity in the V3 region of the visual pathway was reduced, despite the fact that visual inputs didn’t change. Also, neural activity decreased in regions of the parietal and prefrontal lobes that are involved in awareness.
Thus, the motor signals that induce a blink seem to reduce the sensitivity of the visual processing system, telling the brain to disregard any changes in visual signals. The motor signals simultaneously dampen our awareness so that we do not notice the process.
“If the lights go off for same amount of time, it would be very obvious,” Bristow says. “But it looks like this is a way for your brain to dismiss a change because it is something you caused.”