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Unusual Condition Lets People See Sign Language in Colors
Credit: Monika Wisniewska | Shutterstock.com

People who use sign language can experience synesthesia, a rare condition that mixes sensory information from different sources, causing people to see letters in certain colors, or taste words, a new study finds.

The study is the first to document synesthesia among sign language users, the researchers said. The people in the study reported that they saw different colors when they watched someone make the signs for various letters and numbers.

The finding shows that "synesthesia occurs in sign language as well as spoken language," said study lead researcher Joanna Atkinson, a researcher at the Deafness, Cognition and Language Research Centre at University College London. The condition occurs in about 4 percent of the population, including those who experience it with braille letters or while reading sheet music, the researchers said. [10 Things You Didn't Know About the Brain]

Synesthesia is thought to happen because of the wiring in the brain, the researchers said. For instance, this wiring may lead to "cross-activation in neural areas that do not usually interact."

In the study, Atkinson and her colleagues recruited people in the U.S. and the United Kingdom who reported that they were deaf, or used sign language, or had synesthesia, or all of the above. In all, 50 people responded.

Participants underwent a series of tests, which included watching a video of a person spelling out letters and numbers using either American or British sign language. After each sign, the participants were asked to select a color on a chart that best matched their synesthetic perception, or the first color that came to mind, the researchers said.

Among the people who understood sign language, four associated the same letters with the same colors every time, the researchers found. This indicated that these four people had color synesthesia.

None of the participants who did not use sign language reported experiencing synesthesia while watching the videos, the researchers found. This means it's likely that understanding meaning associated with the signs used to make the letters and numbers is necessary to trigger synesthesia, rather than just watching the actions themselves, the researchers said.

Of the four people who used sign language and had synesthesia, "Two reported projection of colors onto the hands and/or fingers; two said they experienced the colors "in the mindꞌs eye" as visual imagery; and one reported "just knowing" what the colors were," the researchers wrote in their study, published online June 28 in the journal Neurocase.

All four of the people with synesthesia had learned signing as a second language, Atkinson said. Three of them had normal hearing, and one was hard of hearing, and had experienced progressive deafness since childhood. [9 Oddest Medical Cases]

More research is needed to determine whether people who are deaf, or who learn sign language as a first language, can experience synesthesia, she said.

Moreover, the four individuals also had synesthesia for written letters, "which they reported transferred to finger-spelled letters," Atkinson said.

There was some evidence that they chose colors based on the form of the hand shape, "particularly where two signs for letter or numbers were visually similar," Atkinson added.

Original article on Live Science.