An international team of researchers has found that people fluent in sign language may simultaneously keep words and signs in their minds as they read.
Judith Kroll, at the Pennsylvania State University, and her colleagues found that deaf readers were quicker and more accurate in determining the meaningful relationship between English word pairs when the word pairs were matched with similar signs.
The slightly better reaction time and improved accuracy rate indicates that the readers are able to juggle both English and sign language at the same time.
"The study shows that sign language users are similar to other bilinguals,' she said.
"This reflects previous research on bilinguals that shows both languages are active even when they're reading or speaking one language," she added.
The researchers tested 19 deaf adults who were fluent in American Sign Language (ASL) as they decided whether pairs of English words were related or unrelated in meaning.
A total of 120 word pairs were divided into two groups of 60 word pairs that had either related or unrelated meanings.
Of the related pairs, such as bird-duck, 14 also had similar signs while 16 of the unrelated word pairs had similar signs.
In ASL, signs are considered related if they have similar hand shapes, locations, movements or orientations.
The researchers added a number of randomly assigned word pairs to complete the test.
When the participants encountered word pairs and signs that were related, the reaction time was significantly faster and more accurate than the reaction of a control group made up of 15 bilingual speakers who spoke English as a second language.
When the word pairs were matched with unrelated signs, the participants' reaction time was slower and less accurate.
The findings have been published in a recent issue of Cognition.