It's one of the most frustrating feelings: You know the word exists, and you know what it means, but you just can't spit it out.
New research suggests the forgetfulness may have to do with how frequently we use certain words.
The findings could help scientists understand more about how the brain organizes and remembers language.
For insight into the phenomenon, researchers tested people who speak two languages, as well as deaf people who use American Sign Language (ASL) to communicate.
"We wanted to look at whether we saw a parallel in signers – do they have a tip-of-the-finger state?" said Karen Emmorey, director of the Laboratory for Language & Cognitive Neuroscience at San Diego State University.
Emmorey and her colleagues found that yes, signers did experience tip-of-the-fingers, and about as often – roughly once a week – as speakers do.
Furthermore, just as speakers can often recall the first letter of the word – as in, "I know it starts with a 'b,'" – signers could sometimes think of part of the sign. In fact, signers were more likely to retrieve a sign's hand shape, location on the body, and orientation, than they were to remember its movement.
Emmorey sees this as a parallel with speakers, where both groups can more often access information from the beginning of the word.
"There's something privileged during language production about the beginning," she said.
One leading idea for what causes these annoying lapses is that when people try to think of a specific word, some other, similar-sounding word may come up in the brain and "block" their ability to access the correct word. This mechanism is called phonological blocking.
To test this idea, Emmorey's team compared bilingual speakers and people who could both speak English and sign ASL.
Previous research has shown that bilingual people have more tip-of-the-tongue moments than those who speak only one language. Some experts have suggested that this is because people who speak two languages have twice as many possible words in their heads to act as phonological blockers.
If that were the case, the scientists reasoned, this shouldn’t occur for people who are bilingual in spoken English and American Sign Language, since the signs and the words don't "sound" the same and shouldn't block each other.
But when they compared these people to bilinguals who spoke English and Spanish, they found that both groups had tip-of-the-tongue/finger states about equally as often. That suggests that phonological blocking is not to blame.
Instead, Emmorey said she suspects this kind of forgetfulness is due to infrequency of use; basically, the less often you use a word, the harder it is for your brain to access it.
This explanation could account for why tip-of-the-tongue is more common in all types of bilinguals, because for people who know more than one language, all words are used less frequently. For example, if you’re bilingual and you use each language about half the time, then you would use every word in each language about half as often as someone who uses only one language.
Further testing will be needed to confirm this idea, though.
Emmorey presented her research on Feb. 19 at the annual meeting of the American Association for the Advancement of Science in San Diego, Calif.