Visual perception improves in the blink of an eye

Each time we blink, it obscures our visual world for 100 to 300 milliseconds. It’s a necessary action that also, researchers long presumed, presents the brain with a problem: how to cobble together a cohesive picture of the before and after.

“No one really thought about blinks as an act of looking or vision to begin with,” says Martin Rolfs, professor of experimental psychology at Humboldt University of Berlin.

But blinking may be a more important component of vision than previously thought, according to a study published last month in the Proceedings of the National Academy of Sciences. Participants performed better on a visual task when they blinked while looking at the visual stimulus than when they blinked before it appeared. The blink, the team found, caused a change in visual input that improved participants’ perception.

The finding suggests that blinking is a feature of seeing rather than a bug, says Rolfs, who was not involved with the study but wrote a commentary about it. And it could explain why adults blink more frequently than is seemingly necessary, the researchers say.

“The brain capitalizes on things that are changing in the visual world—whether it’s blinks or eye movements, or any type of ocular-motor dynamics,” says Patrick Mayo, a neuroscientist in the ophthalmology department at the University of Pittsburgh, who was also not involved in the work. “That is … a point that’s still not well appreciated in visual neuroscience, generally.”

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he researchers started their investigation by simulating a blink. In the computational model they devised, a person staring at black and white stripes would suddenly see a dark, uniform gray before once again viewing the high-contrast pattern. The interruption would cause a brief change in the stimulus input to neurons in the retina, which in turn could increase the cells’ sensitivity to stimuli right after a blink, they hypothesized.

That idea panned out in a series of behavioral experiments: When participants had to discriminate between black and white striped stimuli oriented either to the left or to the right, they performed reliably better if they had just blinked—and that improvement held up whether the blinks were on command, reflexive or researcher-made, simulated by briefly making the screen go gray.

Another form of eye movement—ocular drift, or the small jitters that happen when a person’s gaze is fixed—can also enhance perception of fine visual details by sweeping more of the visual field across receptors in the retina, the team previously discovered. “Neurons are very sensitive to those temporal changes, so they pick it up,” says lead investigator Michele Rucci, professor of brain and cognitive sciences at the University of Rochester.

But ocular drift is unlikely to improve coarse-grain, or low-spatial-frequency, aspects of a visual scene; retinal cells are still getting the same input if their input only jitters slightly. And this is where blinking has the most impact, Rucci says.

He and his colleagues confirmed that idea experimentally: Participants saw benefits from blinking when they performed the task with low-spatial-frequency, but not high-spatial-frequency, stimuli.

The findings underscore the idea of vision as a “multimodal process,” Rucci says. “In other modalities, this is perfectly obvious, right? For example, in somatosensation, in touch, if I want to make sense of what is the input, as I’m moving my finger, I need to know what is my motion that is generating that temporal change,” he says. “I need to interpret it in order to reconstruct the haptic shape of the object.”

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till, the study is not proof of causality, Rolfs says. “We know that blinks cause better vision,” but whether or not that is put to use for human perception remains to be seen. That is something that the researchers could test in future experiments—such as whether manipulating an environment to be more visually challenging results in more blinks, he says.

Beyond behavior, it would be useful to figure out how this enhanced response is happening at the level of neurons, Mayo says. “They’ve made some really sophisticated models about the brain that are super useful and cool, and make strong predictions,” he says. “The question is, OK, now if you go in and record in whatever your favorite visual brain areas are, is that what they’re going to say?”

Overall, the work represents an important direction for vision research, Mayo says. Despite their regular occurrence and their potential effect on vision, blinks are not typically studied in the lab because they can muddy an experiment, he adds.

Rolfs agrees. Back when he began his career in vision science 20 years ago, researchers would routinely toss out trials during which a participant blinked, he says. “Even now, a large part of the community in vision science tries to avoid eye movements, because they want to isolate the perceptual process—without understanding or acknowledging that the actions are part of that essential process.”

But getting a handle on how eye movements affect vision can help researchers better understand the natural process in a way that traditional laboratory experiments—conducted in dark rooms as participants stare, unblinking, at a white spot on a screen—cannot.

“Pushing in that direction, I think, will be hugely beneficial,” Mayo says. “Because we don’t want to explain laboratory vision. We want to explain everyday vision.”