How do cat eyes inspire researchers in developing imaging technology?
Author, Catherine Heathwood
Role, BBC World Service
Published 4 minutes ago
Reading time: 6 minutes
One foggy night in 1933, Percy Shaw was driving home, when a light appeared on the side of the road and stopped him.
The common story is that the source of the light was a cat, the car's headlights reflected in its eyes, and the light returned directly to Shaw.
When Percy Shaw stopped, he discovered he was driving in the wrong direction and would have been on the verge of falling off a cliff if he had not seen the light, his grandniece, Glenda Shaw, told the BBC.
Therefore, this moment not only saved Percy Shaw's life, but also inspired him to invent those light-reflecting signs, "road spikes" that are installed on traffic roads, and the British call them "cat's eyes."
By the time of Shaw's death in 1976, there were 15 million of these "cat eye" signs made, and they are still in use around the world to this day.
On his way to inventing “cat eyes,” Shaw followed a “trial and error” method, according to his grandniece, who said that “he was not an expert in physics, reflections and refractions of light, angles, and dimensions, and he set out to discover the matter for himself.”
Shaw's initial design did not match the design of cat eyes, however, so he tried to mimic the reflection of the light that stopped him on the road that night, using glass beads for this purpose.
How do cats' eyes shine?
Cats' eyes appear to glow in the dark, due to a layer of reflective tissue behind the retina known as the "opaque mat," a special feature humans don't have, according to Brady Foote, a veterinary ophthalmologist and researcher at the University of Tennessee.
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This reflective layer turns the cat's eye into something similar to a mirror, improving its ability to see in low light while hunting at night. It gives the eye a second opportunity to capture light that would otherwise be lost.
Researcher Brady Foote says: “When light does not find a photoreceptor to fall on, it is lost; but within the range of eyes that contain a transparent, reflective mat (such as a cat’s eyes), the light finds something to reflect upon when it collides with this mat, which acts as a mirror, and bounces back toward any other photoreceptor.”
The researcher explains the reason for feeling the brightness of this reflected light is that the pupil of the eye usually dilates in dark environments, which enhances the feeling of this brightness.
The color of this light varies from one cat to another, from orange and yellow to green, according to the pigments present in the fabric.
Cats are not unique in having light-reflecting eyes. There are other animals whose eyes also shine, such as dogs, horses, and cows.
Cameras inspired by cat eyes
Decades after Percy Shaw's invention, engineers are now inspired by the anatomy of cat eyes to develop high-resolution imaging technology and design cameras that can be installed in robots, drones or self-driving vehicles.
Among these engineers is Yang Min-sung, an electrical engineering researcher at the Korea Advanced Institute of Science and Technology, who wants to develop a camera capable of working in environments with varying levels of light, and taking pictures of objects in the middle of crowded oceans.
To achieve this goal, Song first tried to mimic the transparent, reflective layer found in cats' eyes.
In true cats, this layer consists of cells containing rod-shaped crystals - riboflavin and zinc - arranged in such a way that they reflect light.
But through experimentation, it became clear to the researcher that simulating this “nano” structure was an extremely difficult matter, so he and his team turned to using a silver reflective material instead of that layer, and placed this silver material behind the image sensor to create an artificial reflector, and was thus able to increase the camera’s absorption of visible light by 52%.
Next, researcher Song turned to another feature of cat eyes, which is the visible slit shape in the pupil from which light shines.
Researchers believe that this “narrow vertical” slit helps cats measure distances, enabling them to catch hidden prey, even under dense grass cover.
In this regard, researcher Song said: “If I could develop a camera that mimics a cat’s eye with a vertical pupil, this would be useful in getting rid of all the annoying backgrounds that appear in the images, which would contribute to increasing the clarity and distinction of the object being photographed.”
Vision systems in modern computers can isolate the object being photographed from its surrounding environment, similar to smartphones that are able to blur the background in the images they take. But doing so requires high processing power.
Researcher Song's idea was to include this ability directly within the camera itself, by designing a vertical lens aperture that mimics the pupil of a cat's eye.
To test the idea, Song's team photographed an object in a crowded environment using two cameras: one with a vertical lens, and the other with a regular circular lens.
In the image taken with a camera with a circular lens (circular pupil), the target object appeared and the objects in the background of the image appeared with the same degree of clarity, while in a camera with a vertical pupil (vertical aperture), the target object appeared clearer than the objects in the background.
Currently, the aperture has to be changed manually rather than automatically adjusting to light levels like a cat's eye does, a challenge Song says he wants to solve in the future.
Other eyes worth emulating
In addition to cameras inspired by cat eyes, researcher Song and his team have developed several other cameras that mimic the eyes of other animals.
It is believed that there is potential to develop hundreds of designs inspired by nature.
In 2013, Song designed a camera inspired by the eye of a fly, as the researcher believes that “flies have large eyes compared to their bodies, enabling them to see in all directions at the same moment.”
Song believes that this camera has a remarkable ability to explore a wide range and a high speed in distinguishing objects, making it “perfectly suitable for use in robotic drones.”
The researcher believes that if cameras could be developed that mimic the eyes of this type of spider, they could be used in tasks that require measuring distances accurately, as in missile guidance systems, for example.
While current camera systems mostly mimic the human eye, as is the case with cell phone cameras, Song believes that developing cameras that mimic animal vision systems could contribute to specialized applications, “whether in the robotics industry, drones, or any of the next generation robotic systems,” according to the researcher.
