Presque vu
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The tip of the tongue (TOT) phenomenon is an instance of knowing something that cannot immediately be recalled.  TOT is a near-universal experience with memory recollection involving 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. Despite failure in finding 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 two key features of an operational definition of TOTs (A.S. Brown, 1991).

# History of Tip of the Tongue
The experience of TOT appeared in non-academic literature as early as 1885.  Anton Chekhov's short story "A Horsey Name" is about the main character's tip-of-the-tongue experience involving a surname.  In 1890, pioneering psychologist William James discussed the phenomenon in his text The Principles of Psychology. James described the TOT state as "a gap that is intensely active".
In 1966, Harvard psychologists Roger Brown and David McNeill reported the first empirical investigation of the tip-of-the-tongue state.  They recounted, "he signs of it were unmistakable" and "he  would appear to be in mild torment, something like on the brink of a sneeze, and if he found the word his relief was considerable."  They also found that TOT is a fairly universal phenomenon, TOTs occur about once a week and increase as you age, and they're often caused by proper names.  Further, people experiencing TOT are often able to access the first letter of the "target word" fairly accurately and they also bring up words related to the "target word."  Finally, R. Brown and McNeill have some good news: target words are retrieved during the experience of a TOT phenomenon about half of the time (A.S. Brown, 1991).
Although it is not explicitly called by this name it is interesting to note that TOT is briefly considered by Aristotle in "On Memory and Reminiscence", in his discussion on recollection. (453a, 28)

# Recent TOT literature

## Universality
Cognitive psychologist Bennett Schwartz examined fifty-one languages and found that forty-five of them include expressions using the word tongue to describe the TOT state.  Some languages use multiple metaphors.  In Korean, the metaphor "going round and round at the end of the tongue" is used, as well as "caught in the throat." French speakers use the "tongue" metaphor. In some languages, tongue is often replaced by lip, "I got it (the word) right on my lips", the concept remaining identical, and having an obvious relation to the tongue. The results of the language survey suggest that the use of the "tongue" metaphor is not idiomatic to English but instead a commonality of the TOT phenomenon.  Research involving diaries kept of TOT experiences show that college students have approximately one or two TOTs per week, while elderly adults have about two to four TOTs per week (Schacter, 2001).  TOTs occur most frequently for names of people, but for common words as well.

## Etiology and the TOT in different psychology subdisciplines
A second major landmark study of TOTs was a review paper by A.S. Brown (1991), who detailed the pertinent research that had been done on TOTs for the 25-year period since R. Brown and McNeill (1966).  In most sections of his review, A.S. Brown raised theoretical questions about TOTs that warrant further study, but most remain untested today.  Instead of duplicating this coverage, Schwartz (1999) explored the etiology of the phenomenon.  Schwartz considers TOTs in light of Tulvings (1989) critique of the doctrine of concordance and how it applies to the etiology of TOTs.  The doctrine of concordance states that cognitive processes, behavior, and phenomenological experience are highly correlated.  In Tulvings view, cognitive processes should not be confused with the study of phenomenological experiences.  For example, the cognitive process of retrieval is not the same thing as or comparable to the experience of recollection.
The TOT has been studied using three different subdisciplines as approaches:  psycholinguistics, memory perspectives, and metacognition.  The first two are consistent with concordance and argue for direct access (a view that TOTs and word retrieval are caused by the same retrieval processes), while the metacognitive approach challenges concordance.
Most research to date concerning TOTs has come from the psycholinguistic perspective.  This perspective focuses on TOTs as a temporary breakdown in lexical retrieval.  This approach has linked TOTs to other errors in spoken language, such as slips of the tongue and spoonerisms.  Researchers from the memory perspective have viewed TOTs as a marker of retrieval processes gone awry.  Metacognitive models focus on the role that monitoring and controlling processes play in cognition.  This approach views TOTs as inferences based on non-target information that is accessible to rememberers.
The direct-access views of the psycholinguistic and memory perspectives fall into three basic hypotheses.
- The first is the blocking hypothesis which states that TOTs occur because the rememberers recognize blocking words as incorrect but cannot retrieve the correct but inhibited target.
- The second is the incomplete activation hypothesis which views that TOTs are caused by the sensitivity to the existence of an unrecalled target in memory, accompanied by the failure to retrieve the target into conscious memory.
- The third hypothesis is the transmission deficit model which states that TOTs are brought about when the semantic representation of the word is activated, but there is a failure to prime the complete phonological representation of the target word.
The psycholinguistic approach views TOTs as a "window" on word retrieval (Schwartz, 1999).  In 2000, Deborah Burke and Lori James reported on their research employing a repetition priming paradigm that utilized prime words that shared phonological components with potential TOT target words.  They concluded that their results "support the transmission deficit model that the weak connections among phonological representations that cause TOTs are strengthened by production of phonologically related words" (Burke & James, 2000, p. 1378).
Providing support for the direct-access views are research subjects recognition of TOT targets and their ability to give partial information of TOT targets.  Recognition of the correct target following a TOT experience is much greater than recognition of the correct target when subjects are not experiencing a TOT.  And research subjects can usually recall phonological information related to the TOT targets, such as the first letter of the word, the number of syllables, and the syllabic stress.

# TOT and Neurobiology

## Neural basis of TOT
The anterior cingulate and right middle frontal cortices are two neural areas implicated in the TOT phenomenon.  One study showed that, relative to successful retrieval or unsuccessful retrieval not accompanied by a TOT, retrieval failures accompanied by TOTs elicited a selective response in anterior cingulate-prefrontal cortices.  The study also found that while attempting to retrieve information, subjects rely 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 extent that the subjects in our fMRI study used a visual imagery strategy when in a TOT condition, the activation observed in right inferior PFC could constitute the neural correlates of these efforts to resolve these retrieval failures" (Maril et al., 2001, p. 657).

## Three stage neural network model
File:Neural network.svg
One theory of why the tip of the tongue phenomenon occurs comes from Petro Gopych (2001), a professor at the Kharkiv National University. Gopychs model proposes three stages in word recall process.
- Word node selection
This first stage involves actually selecting which word we are trying to recall. When specifying the word, we identify the learned artificial neural network (ANN) which contains information about the target word, and then activate that part.
- This first stage involves actually selecting which word we are trying to recall. When specifying the word, we identify the learned artificial neural network (ANN) which contains information about the target word, and then activate that part.
- Word retrieval
According to Gopych, free recall exhibits positive and negative outputs randomly in the learned ANN. When trying to recall a specific word, otherwise known as cued recall, the retrieval process depicts a spike of these outputs with a fixed part of the true information (specific word). The result of attempts to retrieve the word from the learned ANN is an output of positive and negative units.
- According to Gopych, free recall exhibits positive and negative outputs randomly in the learned ANN. When trying to recall a specific word, otherwise known as cued recall, the retrieval process depicts a spike of these outputs with a fixed part of the true information (specific word). The result of attempts to retrieve the word from the learned ANN is an output of positive and negative units.
- Comparison of patterns
The pattern of outputs determined by the retrieval attempts is compared to a reference pattern from metamemory. If the sample pattern matches the reference pattern, the searching stops because the word that was searched for is recalled. If there is no match, the retrieval process (stage 2) starts over again and a pattern of outputs enters the ANN. This continues until the reference pattern is detected or the process is stopped independently.
- The pattern of outputs determined by the retrieval attempts is compared to a reference pattern from metamemory. If the sample pattern matches the reference pattern, the searching stops because the word that was searched for is recalled. If there is no match, the retrieval process (stage 2) starts over again and a pattern of outputs enters the ANN. This continues until the reference pattern is detected or the process is stopped independently.
Gopych believes that the problem in recalling a specified word comes from a damaged ANN. He suggests that the stored semantic information is damaged or incompletely selected. The severity of the damage determines the power of the TOT.
Gopychs three stage neural network theory can be used to explain many aspects of TOT including semantic priming, immediate, delay, or eventually full TOT resolution, age dependence in TOTs, recollection of the first letter of the target word, and many more. Using the number of attempts of memory retrieval, the duration of time intervals between successive sets of spikes, and the duration of single neuron spikes, the retrieval chronometry can be determined. Gopychs theory also supports Tulvings challenge to the doctrine of concordance.

# TOT across the lifespan
TOT research in children has mainly focused on when they begin to experience TOTs and what the experience is like for them (Brown, 1991).  Wellman (1977) found evidence that children between kindergarten and third grade (ages 4-7) did experience TOTs, though very rarely.  They were able to recall pieces of the target word, words that sound like it or rhymed with it, and long words that included it.  Further, they would tell researchers that they knew the word, but were having trouble remembering it.  Like adults, they also became uncomfortable and frustrated by the experience.  Finally, his findings suggest that TOTs occur more often in third graders (ages 6-7) than they do in kindergarteners and first graders.
More research has been done with TOTs in older adults.  In terms of subjective estimates, research has found that older adults report experiencing TOTs about as often as younger adults (Brown, 1991).  However, studies by Burke et al. (1991) and Cohen and Faulkner (1986) with more objective measurements received different results.  Their participants kept diaries for four weeks, recording their TOT experiences, and young adults were found to experience significantly fewer TOTs than older adults.  Other TOT literature has found that older adults remember less information about the target word and bring up fewer related words during the TOT experience and are less active in resolving the TOT experience (Brown, 1991).