Humans normally see only wavelengths in our visible light spectrum. Some animals can see other wavelengths that include ultraviolet light.
Some humans though can see ultraviolet light. The impressionists painter Claude Monet had cataracts when he was elderly, the change in his eye lens made him see colours with a more redder tint than was normal or that he had seen them before.
After an operation to remove his cataracts it is believed he could suddenly start to see ultraviolet light. Monet's painting changed with a lot more whiter/bluer colours in his paintings.
Claude Monet ultraviolet light paintings
Monet's cataracts left him struggling to paint; he complained to friends that he felt as if he saw everything in a fog. After years of failed treatments, he agreed at age 82 to have the lens of his left eye completely removed. Light could now stream through the opening unimpeded. Monet could now see familiar colors again. And he could also see colors he had never seen before. Monet began to see and to paint in ultraviolet.
Monet's Ultraviolet Eye
Aphakia and seeing ultraviolet light
The brain itself does not seem to block out or not process ultraviolet light, it just does not normally get through our eyes lens.
Other humans who can view ultraviolet wavelengths
Alek Komar is the most documented person who can see the electromagnet spectrum part that includes ultraviolet light waves. (Click here to read short article about Alek Komar and Aphakia).
Humans dont see UV light because we normally only have 3 types of cones in our eyes (trichromats). Animals who can see ultraviolet have 4 cone types (tetrachromats). But there may be humans who were born with the natural ability to see a wider range of natural electromagnetic wavelengths including ultraviolet.
Women who carry a copy of the OPN1MW gene on one X chromosome and OPNMW2 on the other may possess four separate types of cones rather than the usual three.
The eyes have it: Seeing ultraviolet, exploring color
Ancient humans may have seen other wavelengths?
The human body has changed over the years. Perhaps some of the ancient humans could have seen other wavelengths including ultraviolet? If their lenses were different or if they had different light sensors to what we have today?
Perhaps evidence that previous races could see different electromagnetic wavelengths comes from the ancient Vajra weapon of the god Indra that looks similar to electromagnetic images of Jupiter.