March 18, 2024 06:00 | Updated at 06:00 AM IST – Bengaluru
Animal vision video can help farmers spot fruit pests invisible to the human eye but easily visible to some animals
This illustration compares three flowers – summer snowflake (A, B), blue phlox (C, D) and blue violet (D, E) – in false honey bee color (left) and human-visible colors (right). | Photo: Vasas V, et al., 2024, PLOS Biology, CC-BY 4.0
To most people, leaves are green and oranges are orange. But if our pets could talk, they wouldn’t agree.
We know that there are many different ways to “see” the world because that is the diversity we have found in animals. Organisms with the ability to see have two or more eyes that capture light reflected from various surfaces in their surroundings and convert it into visual cues. But while all eyes have this common purpose, the specialized cells that respond to light, called photoreceptors, are unique to each animal.
For example, human eyes can only detect wavelengths of light between 380 and 700 nanometers (nm); this is the visible range. Honey bees and many birds on the other hand can also “see” ultraviolet light (10-400 nm).
Although the human visual range is relatively limited, it has not diminished people’s curiosity about how animals see the world.
Fortunately, we don’t have to imagine too much. Researchers from the University of Sussex and George Mason University (GMU) in the US have created a new camera with the ability to see the world like animals. In an article published in PLoS Biologythe team wrote that their device can even reveal what colors different animals see in motion, which has not been possible before.
Making the invisible visible
Animals use colors to intimidate their predators, attract mates, or camouflage themselves. Detecting color variation is therefore essential for animal survival. Animals have evolved to develop highly sensitive photoreceptors that can detect light of ultraviolet and infrared wavelengths; many even notice polarized light as part of their Umwelt—the biological systems that make possible a specific system of meaning-making and communication.
Neither human eyes nor most commercial cameras have been able to touch this uncharted territory of animal vision. In the new study, biology, computer vision and programming came together to create a tool that can record and track the complexity of animals’ visual signaling.
The instrument combines existing multispectral photography techniques with a new camera setup and beamsplitter (to separate ultraviolet and visible light), all wrapped in a custom 3D-printed device. The system records videos simultaneously in visible and ultraviolet channels under natural light. They fed the camera output through some code (written in Python) that could convert the visual data into the physical signals produced by the photoreceptor cells.
Finally, the researchers modified these signals based on what they already knew about how the animals’ photoreceptors work and created videos that were true to what the animal could see. They used false colors in these videos so that, for example, a certain color could stand to show ultraviolet images.
In short, the camera system translates what animals see in visible and invisible light into colors compatible with the human eye.
The challenge of time
You may have seen false color images before – like when you saw the iconic photo of the “Pillars of Creation” on the Hubble Space Telescope. Stars and nebulae don’t really look that bright to the human eye. They are colored this way to show what the telescope has seen in, say, infrared or radio wavelengths. Scientists have also used false-color images to understand how flowers reflect ultraviolet light to influence the behavior of nearby insects.
But false colors can only replace so much. According to the researchers, existing techniques for visualizing the colors animals see require light reflected from an object to predict how an animal’s photoreceptor will respond, or require a series of photographs at wavelengths beyond human vision (using band-pass optical filters). Both scenarios require the object to be stationary. However, the new system can visualize free-living organisms in their natural settings.
In addition, Pawan Kumar Reddy Katha, a graduate assistant at GMU and one of the study’s authors, said the team has written a program that can take both ultraviolet and visible light data and spit out full videos. “We used a continuous stream that allowed us to resolve our data at different points in space and time and create real-time visualizations in animal vision,” he told this author.
The next big thing in animal vision
Equipped with the new camera, the research team checked what the black-eyed Susan flower was (Rudbeckia hirta) looks like honey bees (Apis mellifera).
“To our eye, the black-eyed Susan appears entirely yellow because in the human-visible range it reflects primarily long-wavelength light,” the team wrote in their paper. “While in the false-color image of the bee, the distal petals appear purple because they also reflect UV light, stimulating both UV-sensitive photoreceptors … and those sensitive to green light … In contrast, the central part of the petals does not reflect UV light and therefore appears red.”
According to the paper, the visual mechanisms that animals have evolved to communicate and defend themselves can help solve many of our detection problems. For example, animal vision video can help people better navigate wild landscapes without harming camouflaged animals. It can help farmers spot pests on fruit that aren’t visible to the human eye, but are easily visible to animals that have evolved to eat those fruits.
Daniel Hanley, assistant professor at GMU and corresponding author of the study, said their invention could even transform the way wildlife documentaries are made. The camera system could allow filmmakers and conservationists to record wildlife through a new lens and create new visual experiences. He also said the platform’s astonishing images could be used to communicate the science of the living world to young audiences.
“We are thinking of creating a science exhibition for children using our setting, flowers and live animals,” Dr Hanley said. “Where kids can just click a button to experience what a snake or a honey bee can see.”
Sanjukta Mondal is a chemist turned science writer with experience writing popular science articles and scripts for STEM YouTube channels.
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