Apparently, we see the world in higher resolution than most animals do.
Compared with many animals, human eyes aren’t particularly good at distinguishing colors or seeing in dim light. But, according to a group of researchers at Duke University, our eyes do excel by at least one measure which is called visual acuity and essentially means the clarity of vision.
There are exceptions, of course – for example, birds of prey like eagles see fine details twice as well as us – but human visual acuity (which is similar to chimpanzees’) is superior to that of most other animals, according to the new findings published in Trends in Ecology & Evolution.
The researchers reviewed the results of past studies that analyzed the eye anatomy or behavior of 600 species of animals and found a 10,000-fold difference between the sharpest and fuzziest vision. Humans, chimps, and birds of prey – interestingly along with octopuses – were on the top of the list, closely followed by a whole host of mammals. Perhaps rather foreseeably, different insect species ranked worst in the comparison.
The team then used the AcuityView software to create images that demonstrate how clearly animals see their surroundings. Below are some examples.
The images thus generated call into question the purpose of certain animal features. Take the patterns on a butterfly’s wing, for example, the function of which have long been debated by scientists. Humans can easily make out these spots and markings, but weirdly other butterflies most probably can’t (see image above), which suggests that they have more to do with deterring or confusing predators than attracting mates.
Some animals may use such differences in acuity to send secret messages that sharper-sighted species can read but others can’t. For instance, orb-weaver spiders decorate their webs with white silk spirals, zigzags, and other designs whose function has been debated. But if we look at images of spider web decorations as they might appear to other species, it turns out that while birds can spot them from as far away as six feet, they are virtually invisible to small insects that might wander into the spider’s sticky traps. So apparently the function of the decorations is to alert birds to webs without letting possible prey know about them.
The researchers point out that the images they’ve created don’t represent what animals actually see in real life – they simply illustrate an animal’s visual acuity. The reason for this is that while the eyes take in visual information, the brain still must process it. According to lead author Eleanor Caves, some things could be sharper or easier to detect due to post-processing mechanisms, such as edge enhancement, that occur once the visual information is relayed to the brain. Nevertheless, the software gives researchers a good sense of what kind of visual information the brain has to work with.
“The point is that researchers who study animal interactions shouldn’t assume that different species perceive detail the same way we do,” Caves said.