Human Eyesight is Sharper Than It Is For Most Animals

The ability to see detail is known as visual acuity.  Researchers from Duke University set out to estimate the visual acuity of more than 600 species  of insects, birds, mammals, fish and other animals. It turns out, humans are pretty good at detecting detail.  The researchers look at behavioral tests and eye anatomy such as the spacing and density of light-sensing structures to determine the amount of detail each species could detect.

The researchers concluded that most of the animal kingdom sees the world in far less detail than humans do.  There are some animals such as certain birds of prey that see in a much higher resolution than humans.  This higher visual acuity helps eagles spot small rodents and rabbits running through a grassland while flying thousands of feet above them.  For example, the wedge-tailed eagle of Australia has twice the visual acuity of humans.  Fish, on the other hand, have half the acuity of humans.  Humans can see detail four to seven times as great as cats or dogs.  Humans see detail more than a hundred times greater than mice.

How well can you see compared to a cat, fish, rat, fly, or mosquito? Visual acuity simulation from Caves, 2018.

How well can you see compared to a cat, fish, rat, fly, or mosquito? Visual acuity simulation from Caves, 2018.

To provide a sense of what differences in visual acuity look like, the researchers wrote a R package called AcuityView, that strips out detail from images to mimic the eyesight of difference species.  While the images aren’t intended to precisely replicate what each species can see, the images serve to illustrate just how blurry an object becomes depending on measured visual acuity.

References

Caves, E. M., Brandley, N. C., & Johnsen, S. (2018). Visual acuity and the evolution of signals. Trends in ecology & evolution.

Caves, E. M., & Johnsen, S. (2018). AcuityView: an R package for portraying the effects of visual acuity on scenes observed by an animal. Methods in Ecology and Evolution, 9(3), 793-797.

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