The ordinary act of blinking takes up a surprising amount of our waking time. Humans, on average, spend a remarkable 3 to 8 percent of their awake time with their eyelids closed.
Given that blinks prevent an image of the external scene from forming on the retina, it's a peculiar quirk of evolution that we spend so much time in this seemingly vulnerable state—especially considering that eye blinks occur more frequently than necessary just to keep our eyes well lubricated.
So why is blinking important?
Researchers from the University of Rochester investigated the curious case of blinking and found that eye blinks aren't just a mechanism to keep our eyes moist; blinks also play an important role in allowing our brains to process visual information. The researchers published their findings in the Proceedings of the National Academy of Sciences.
"By modulating the visual input to the retina, blinks effectively reformat visual information, yielding luminance signals that differ drastically from those normally experienced when we look at a point in the scene," says Michele Rucci, a professor in the Department of Brain and Cognitive Sciences.
The big picture—in the blink of an eye
Rucci and his colleagues tracked eye movements in human observers and combined this data with computer models and spectral analysis—analyzing the various frequencies in visual stimuli—to study how blinking affects what the eyes see compared to when the eyelids are closed.
The researchers measured how sensitive humans are at perceiving different types of stimuli, such as patterns at different levels of details. They found that when people blink, they become better at noticing big, gradually changing patterns. That is, blinking provides information to the brain about the overall big picture of a visual scene.
The results show that when we blink, the rapid motion of the eyelid alters the light patterns that are effective in stimulating the retina. This creates a different kind of visual signal for our brain compared to when our eyes are open and focused on a specific point.
"We show that human observers benefit from blink transients as predicted from the information conveyed by these transients," says Bin Yang, a graduate student in Rucci's lab and the first author of the paper. "Thus, contrary to common assumption, blinks improve—rather than disrupt—visual processing, amply compensating for the loss in stimulus exposure."
Revising a view of vision
The findings further reinforce the growing body of research in visual perception from Rucci's laboratory, highlighting that how humans see is a combination of sensory input and motor activity. When we smell or touch, for instance, our body movements help our brain understand space. Researchers previously believed seeing was different, but Rucci's research lends support to the idea that vision is more like the other senses.
"Since spatial information is explicit in the image on the retina, visual perception was believed to differ," Rucci says. "Our results suggest that this view is incomplete and that vision resembles other sensory modalities more than commonly assumed."
