A new study in the journal Nature helps to explain how specialized retinal cells help stabilize vision by perceiving how their owner is moving.

Think of the way that a long flat highway seems to widen out around you from a single point on the horizon, while in the rear–view mirror everything narrows back to a single point behind you. Or think of the way that when a spaceship in a movie accelerates to its “warp” or “hyper” speed, the illusion is conveyed by the stars turning into streaks that zip radially outward off the screen. That’s how a new study says specialized cells in the retina sense their owner’s motion through the world – by sensing that same radiating flow.

The finding is part of a broader discovery, made in the retinas of mice, that may help explain how mammals keep their vision stable and keep their balance as they move, said senior author David Berson, a professor of neuroscience at Brown University.

The brain needs a way to sense how it is moving in space. Two key systems at the brain’s disposal are the motion–sensing vestibular system in the ears, and vision — specifically, how the image of the world is moving across the retina. The brain integrates information from these two systems, or uses one if the other isn’t available (e.g., in darkness or when motion is seen but not felt, as in an airplane at constant cruising speed).

“Good cameras have gizmos that stabilize images,” Berson said. “That’s just what the retinal motion and vestibular systems do for our own eyes.

“Once things are smearing across your retina, your whole visual system just doesn’t work as well,” Berson continued. “You can’t resolve detail, because the image of the whole world is moving on your retina. You need to stabilize images to make those judgments accurately and, of course, sometimes your life depends on it.”

So how is this done? From observations of thousands of retinal neurons led by lead author Shai Sabbah, a postdoctoral scholar at Brown, and Berson, here’s what the research team learned: Direction–selective ganglion cells (DSGCs) become activated when they sense their particular component of the radial optical flow through the mouse’s vision. Arranged in ensembles on the retina, they collectively recognize the radiating optical flow resulting from four distinct motions: the mouse advancing, retreating, rising or falling. The reports from each ensemble, as well as from those in the other eye, provide enough visual information to represent any sort of motion through space, even when they are combinations of directions like forward and up.

The information from the cells is ultimately even enough to help the brain sense rotation in space, not just moving forward, backward, up or down — motion known as translation. Sensing rotation is crucial for image stabilization, Berson said, because that’s how the eyes can stay locked on something even while the head is turning.

“One of the biggest mysteries that is revealed by our findings is that a motor system that will generate a rotation of the eye in service of image stabilization is ultimately driven by a class of retinal cells organized around the patterns of motion produced on the retina when the animal translates through space,” Berson said. “We don’t fully understand that yet, but that’s what the data are telling us.”