We investigated whether individuals are able to differentiate being in a tip-of-the-tongue state from the metacognitive experience of knowing information, but being unable to recall it. Results indicate that being unable to recall known information is separate from, and more common than, experiencing a tip-of-the-tongue state.
Gingerich, Amanda C., "Feeling of Knowing and Retrieval Failure: Tip-of-the-Tongue State is Not the Only Option" (2010). Scholarship and Professional Work - LAS. Paper 184.