Scientists have discovered a previously unknown function of blinking

Every few seconds, we blink our eyes — a simple, involuntary act. While it’s commonly understood that blinking keeps our eyes lubricated, a new study by researchers from the University of Rochester has uncovered a more intricate role: blinking also helps our brains process visual information more effectively. Published in the Proceedings of the National Academy of Sciences, the study sheds light on how these brief closures of our eyes contribute to visual perception.

Humans spend about 3 to 8 percent of their waking hours with their eyes closed due to blinking. Given that blinking briefly obscures our vision, one might wonder why it occurs so frequently. Traditional explanations have highlighted its role in maintaining eye moisture and preventing dryness.

However, the frequency of blinks suggests that there might be additional functions beyond lubrication. Researchers Bin Yang, Janis Intoy, and Michele Rucci sought to explore these potential functions, particularly how blinking might influence visual processing in the brain.

Their study included twelve participants, consisting of both women and men with an average age of 22 years, all possessing normal vision. Participants were compensated for their time and kept unaware of the specific aims of the study to ensure unbiased results. The researchers conducted the study in a controlled laboratory environment, using advanced eye-tracking technology to monitor participants’ eye movements precisely.

Participants were tasked with viewing visual stimuli consisting of grating patterns, which are alternating stripes varying in spatial frequency. Spatial frequency refers to the level of detail in the pattern, with higher frequencies indicating finer details. These stimuli were displayed on a high-resolution monitor, and participants had to identify whether the gratings were tilted clockwise or counterclockwise.

The experimental design included two main conditions to isolate the effects of blinking on visual processing. In the “Stimulus-Blink” condition, participants were cued to blink during the presentation of the visual stimulus. In contrast, in the “No-Stimulus-Blink” condition, they were cued to blink before the stimulus appeared. The researchers controlled the timing and conditions of the blinks to ensure that any observed effects could be attributed to the act of blinking itself rather than other variables.

Eye movements were tracked using a Dual Purkinje Image eye-tracker, which provided high-resolution data on the position and movement of the participants’ eyes. This technology allowed the researchers to ensure that the participants were following instructions and that their blinks and eye movements were accurately recorded. Each experimental session consisted of multiple trials, and data were collected and analyzed to compare performance between the two conditions.

The researchers found that when participants blinked during the presentation of the visual stimulus, their performance in identifying the grating’s orientation improved significantly compared to when they blinked before the stimulus appeared. This improvement was evident in both the accuracy of their responses and their sensitivity to the visual details, measured by a standard discrimination sensitivity index.

The researchers hypothesized that this improvement was due to the luminance changes caused by blinks. Luminance refers to the brightness of the visual stimulus. When we blink, the temporary closure of our eyes creates abrupt changes in luminance. These changes may help reset the visual information entering the eye, thereby aiding the brain in processing the visual input more effectively.

“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,” explained Rucci, a professor in the Department of Brain and Cognitive Sciences.

To test this hypothesis further, the researchers conducted a control experiment where they simulated the effects of blinks by briefly dimming the visual stimulus. Participants’ performance improved in a similar manner to when they blinked naturally. This supported the idea that the luminance changes themselves, rather than the physical act of blinking, were responsible for the enhanced visual processing.

The study concluded that blinking during visual tasks enhances the brain’s ability to process visual information by introducing beneficial luminance changes. These findings suggest that blinks play a crucial role in visual perception beyond merely keeping our eyes moist. The results also imply that our visual system has evolved to use these brief interruptions in vision to improve our overall visual acuity and processing.

“We show that human observers benefit from blink transients as predicted from the information conveyed by these transients,” said 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.”

The study, “Eye blinks as a visual processing stage,” was published April 2, 2024.