If butterflies, cats, and people stare together at Da Vinci's Mona Lisa, what will they see? We may never know the answer, but a recent study can provide us with some clues.
The same world, different vision
In fact, for everyone, the feeling of watching "Mona Lisa" may not be the same. The experience of watching this famous painting is likely to depend on your perspective. If you look directly at her from the front, you will find that there is no smile in her mouth; and if you focus your attention elsewhere on the screen, her mysterious smile will show. The appearance of Mona Lisa is likely to depend on our visual acuity. It is theorized that Da Vinci used special painting techniques to allow viewers to see images that are not the same as the focus of line-of-sight when they use edge-vision (small details are captured).
In the human field of vision, the visual acuity differs depending on the focal point of the eye, but in the different species there is a huge difference - the difference between the animal with the highest visual acuity and the lowest animal is 10,000 times. This interesting research was recently published in the Journal of Ecology and Evolution.
"Our human senses are not very good in many respects, but visual acuity is really good. We can see a lot of details," said Eleanor Caves, a biology researcher at Duke University in the United States. Caves and her colleagues read hundreds of animal visual research papers to get basic information. Their research covers birds, mammals, fish, and insects.
Exploring the secrets of visual acuity
The researchers used the term “spatial frequency” (spatial frequency refers to the number of sinusoidal modulations of the light and darkness of the image or stimulus pattern per degree of view) to define the animal’s visual acuity in units of cycles per degree. CPD). Studies have shown that the spatial frequency of the human eye is about 60 cycles/degree, whereas the visual spatial frequency of cats is only 10 cycles/degree, which is lower than the visual acuity of the blind. The visual acuity of the shrimp was only poor 0.1 week/degree. Wedge-tailed eagles have a visual acuity of 140 cycles/degree, so they can recognize the small prey on the ground from thousands of feet in height.
Researchers measured the spatial frequency of animals in two ways. They dissected the animal's retina, measured the density of light-sensitive cells on the retina as photoreceptors, and linked them to spatial frequency values. They conducted behavior studies by placing living animals in a circular container with black and white stripes. When rotating the container, if the animal can feel the stripes, they will feel that they are moving and will respond accordingly. If the animal does not see those stripes, the inner wall of the container with black and white stripes is a stationary gray for it, and even if the container starts to rotate, the animal will not behave in response to the movement.
By changing the rotation frequency and the thickness of the black and white stripes on the inner wall of the container, the researchers can identify how clear the animal's vision is. Caves and her team input animal visual acuity data obtained from the study into the software they developed for image reconstruction. These reconstructed animal visual images show great differences in vision among different species
Visual details and behavior details
Although shrimp and some insects have poor performance in their vision tests, the researchers cautioned that the images in the study only represent the visual acuity of the animals. When the brain processes visual information, other factors also play a role. There are so many species in nature, they may have evolved different ways to understand the world.
However, if the animal's visual acuity is too low to detect enough detail, the brain cannot process it further. The degree of detail in visual information is likely to play an important role in the communication of animals.
Caves said that their work is studying color vision. For example, most insects do not see red, and the erythema on the back of a black widow spider may not be visible to their prey, but for potential predators, the black widow's erythema is a striking warning color. The gorgeous patterns on fish are appealing to the opposite sex, but do not attract low visual acuity or distant predators (the farther the distance, the lower the visual acuity). Spiders may carefully design the spider web pattern. These patterns are invisible to insects, but those birds can see clearly, so as to avoid the spider web being broken.
Researchers will compare animal visual acuity and their behavior in the next step. "We still don't understand how animals see the world. In fact, although you and I are all human beings, I can't tell you what the world I'm feeling is like. So of course we can't fully understand how animals feel."
It's too bad. We can't ask a butterfly flying in front of Mona Lisa: "Have you ever seen the mysterious smile in masterpieces?"