Wikipedia provides a good explanation of TOT It is summarised below;
The tip of the tongue (TOT or Presque vu, from the French for "almost seen") phenomenon is an instance of knowing something that cannot immediately be recalled.
TOT is understood to be an adverse experience or difficulty that we have with our memory recollection. It involves having difficulty retrieving a well-known word or familiar name.
When experiencing TOT, people feel that the blocked word is on the verge of being recovered. So, despite the failure in finding or recalling the word, people have the feeling that the blocked word is figuratively "on the tip of the tongue."
Inaccessibility and the sense of imminence are the two key features of an operational definition of TOTs (A.S. Brown, 1991).
There is a hypothesis that Dyslexia involves phonological processing deficits but not semantic process deficits. To test this hypothesis research scientists brought together a number of children and used tip-of-the-tongue (TOT) responses on a picture-naming task.
Participants in the test included 16 children who were known to be suffering from dyslexia and 31 control children between 8 and 10 years of age who did not differ in receptive vocabulary.
The research seemed to confirm the hypothesis; children with dyslexia demonstrated more TOTs and proportionally more errors in the phonological step of word retrieval but not in the semantic steps. Longer and low-frequency words also prompted more TOTs.
The researchers believe the results provide good evidence of text-independent, on-line phonological processing deficits in readers with dyslexia.
A separate study (Maril et al., 2001, p. 657) also found that while attempting to retrieve information, subjects relied heavily on visual spatial clues in correctly retrieving the information.
For example, some subjects in the study that were trying to recall a name described looking at the person's face in attempting to retrieve the name.
Also, when trying to recall the name of an author, the subjects described attempting to read the name of the author from an imagined book.
The authors of the study suggest that the subjects in the fMRI study used a visual imagery strategy when trying to resolve a TOT condition.
This is something that may be familiar when you consider your own memory recollection strategies and that of your children.
For more information on TOT, including it's use in signing for the deaf and the experiences of multilingual speakers, click on the link to USAToday.