New research has shed some light on why people seem to suddenly forget the very words that were on the tip of their tongue.
Jennie Pyers, a psychologist at Wellesley College in Massachusetts, says that one possible explanation is that similar-sounding words compete for the brain's attention.
Considering that bilinguals know twice as many words as monolinguals, the researcher says that there's more chance for tip-of-the-tongue experiences.
"Often when we're having tip-of-the-tongue experiences, words that sound the same come to mind. There's a sense that you do know the first letter; there's a sense that you might know how many syllables it is," New Scientist magazine quoted Pyers as saying.
The researcher added that another explanation could be that these experiences occor when the brain recalls rarely used words.
"It's much easier to retrieve a word like 'knife' than 'guillotine'," Pyers said.
Given that bilinguals speak two languages, they tend to use many words less frequently than monolinguals.
For their research, Pyers and colleagues compared 11 Spanish-English bilinguals with 22 people who used English and American sign language (ASL).
The researchers said that there was no opportunity for sound-alike words to elicit tip-of-the-tongue experiences because the signers' second "tongue" made no use of sound.
With a view to provoking tip-of-the-tongue moments, the bilinguals and 22 English monolingual control subjects were shown pictures of dozens of different objects, and asked to name them in 30 seconds.
The viewed objects-which included axes, weathervanes, gyroscopes, nooses and metronomes-were obscure enough to elicit tip-of-the-tongue experiences in all but one participant.
The researchers found the monolinguals to have fewer tip-of-the-tongue experiences than bilinguals.
However, the researchers also observed that Spanish bilinguals experienced roughly the same number of tip-of-the-tongues as sign language bilinguals, ruling out the possibility that similar-sounding words compete for our brain's attention in tip-of-the-tongue experiences.
Pyers then said that, more likely, tip-of-the-tongue experiences occur when we're trying to recall rarely used words.
"People often have tip of the tongue experiences for proper names, again because we don't use them very frequently," she said.
A report describing the study has been published in the journal Cognition.