After taking yet another group photo where my eyes were closed, I decided it was time to learn more about the science of eye blinking. Blinks are a rapid closure of the eyelids, lasting between 100-400 milliseconds. A blink physically begins with inhibition of the muscle which normally keeps the upper eyelids in an open position. Then another eyelid muscle that encircles the eye pulls the upper eyelids down, while the lower eyelids moves toward the nose, and the eyes close. Subsequently, those actions reverse and the eyes return to the open position.
Blinks interact with the brain’s vision perception in several ways. For example, during a blink the eyelids block the pupil for hundreds of milliseconds, which should lead to interruption of vision. Consider that an object passing in front of a camera sensor for 100 milliseconds would easily be noticed. Yet blinks are rarely noticed and do not affect visual perception despite occurring thousands of times per day (between14,400 -19,200 over 16-hours!). How is this possible? Well, although not fully understood, scientists suggest that neural mechanisms in various brain regions maintain visual activity without interruption during a blink. This lets the brain ‘fill in’ images despite the transient gap in visual input from the outside world. Another effect of blinking is that the eyes move inward and back by about 1 mm during each blink. The brain accounts for this subtle eye movement, and repositions the eyes to allow continuity of what we see before and after a blink. Without these and several other complex adjustments during blinking, our visual world would be quite fuzzy, shaky and discontinuous.
Blinking has clear eye related functions. Reflexive blinking in the face of threats like blowing particles or bright flashes protects the eyes. Spontaneous blinking maintains the tear film which covers and lubricates the surface of the eyes, but begins drying up about 25 s after a blink. So, just 2-3 blinks per minute suffice to keep the film intact, and the eyes moist. Babies and children blink about 2 times per minute. However, by adolescence, that increases to the typical adult frequency of blinking 15–20 times a minute. This is far more often than necessary for eye health. So, what is with all the blinking?
Studies find that we tend to blink at predictable times. For example, when reading, most people blink at the end of a sentence. When listening to a speech, people blink when the speaker pauses between statements. And when watching a video, people blink when the action lags for a moment. Some scientists believe that blinks may serve to ‘chunk’ incoming information into manageable bits for learning or memory, although this has not yet been clearly established in studies. A recent study using fMRI found that when individuals blinked, activity briefly spiked in areas related to the Default Mode Network of the brain which operates when the mind is in a state of quiet wakeful rest, rather than focusing on some task. The researchers proposed that momentary activation of this network could offer a mental break or rest, allowing for better attention when the eyes open again after each blink.
Interestingly, early studies suggested that we blink far less than usual when looking at computer screens – only about 5 times a minute. However, subsequent testing has shown that the decreased blink rate occurs even when reading printed material of equivalent cognitive complexity. What is different about on screen reading is that there are a high number of incomplete blinks, probably due to visual fatigue from factors like lighting, glare and angle/distance from screen. Incomplete blinking contributes to eye strain, and chronic dry eye. To combat this, ophthalmologists recommend trying consciously to blink more often during prolonged screen use. You may also have come across the 20-20-20 rule: every 20 minutes look away from the screen at something 20 feet away for 20 seconds. Although there are limited data to support this specific rule, frequent breaks from near-vision work are widely recommended by eye specialists. This can be useful when working with printed text for long periods as well.
In addition to cognitive demand, many other factors affect blink rate, such as fatigue, emotions, social or cultural context, and certain neurological disorders. We have also not yet touched on voluntary control of blinking, which is the answer to avoiding eye closure while posing for photos. It appears we will need to continue thinking about blinking in the next blog entry. Do not worry, though, it will be here in the blink of an eye!
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Post by: Nadia Fike
Read more: 1. Nakano T, et al. Blink-related momentary activation of the default mode network while viewing videos. Proc Natl Acad Sci USA. 2013;110(2):702-706. 2. Willett SM, et al. The perceptual consequences and neurophysiology of eye blinks. Front Syst Neurosci. 2023 Aug 16;17:1242654.