Although the neural basis of TOT states is not yet fully understood, we do know that (1) TOTs may involve competition among candidate word representations and the involvement of the anterior cingulate cortex in conflict detection; (2) TOTs may involve recruitment of the prefrontal cortex, possibly to exert top-down control over memory-retrieval efforts such as by priming situationally relevant memory representations or otherwise initiating goal-oriented behavior that is aimed at resolving the TOT state; (3) left hemisphere temporal regions known to be involved in language are likely involved, both in the stalling of retrieval mechanisms that is taking place to prevent successful retrieval of the target word, and also possibly in where the presumed competition among candidate word representations is taking place; and (4) future research is clearly needed in order to determine the extent to which people undergoing left hemisphere sourced anomia experience increases in subjective sensations of TOT states compared to other populations and how separable these TOT states may be from access to partial target attributes.

TOTs are inherently subjective experiences; only the experiencer can really know whether one is happening and what it feels like as it does. As such, methodologies and their nuances are extremely important. This chapter covers the various methods that have been employed to measure TOTs. The prospecting method – now the most widely used method of studying TOTs – was first developed by Brown and McNeill (1966) in their seminal paper. Present-day use of the method commonly employs word definitions, general-information questions, or faces of famous people. The method can also be adapted to new learning. It is also important to determine how accurate TOTs are at predicting later memory, and we discuss approaches to doing so. Another approach to studying TOTs involves diary studies, in which people are asked to record their naturally occurring TOTs and their qualities and characteristics over a set period of time. How TOT rates should be computed remains an important issue. Depending on one's theoretical approach, it can make sense to divide the number of TOTs over all unrecalled items, or it may be better to divide the number of TOTs over TOTs plus correctly recalled items.

Many TOT-related biases have been discovered since the initial inadvertent finding of a TOT-related bias toward inferring the likely study status of an unidentified target word by Cleary (2006). These biases range from inferring fluent characteristics of the unidentified target to inferring fluent partial attributes of the unidentified target to inferring positive emotional qualities of the unidentified target. These TOT-related biases also include a tendency toward exhibiting information-seeking behaviors such as using limited experimental resources to discover the unidentified answer or even deciding to take an unrelated gamble. They also include a tendency toward experiencing illusory partial recollection. Though the exact cause of these TOT-related biases remains a current gap in understanding, they collectively point toward the idea that TOT states do not occur in metacognitive isolation but rather are accompanied by a number of other distinct metacognitive subjective phenomena as well as by biased judgments and decisions about courses of action. Understanding these biases has many implications for understanding the etiology of TOTs and their relation to retrieval.

TOT states are conscious experiences. When we are in a TOT state, we know it and we feel it. A major conclusion from the work presented in this book is that reliance on subjective reports remains a critically important means of investigating the TOT phenomenon. How TOTs influence other thoughts, decisions, and behaviors remains an important area for future investigation. One of the newest areas in TOT research and one that is driving recent research is the finding that TOT states are associated with a number of cognitive biases in the moments that those TOT states are occurring as well as with indicators of goal-oriented behaviors aimed at information-seeking and possibly ultimately at TOT resolution. This research shows that TOTs help to put people on a path toward resolution, enabling and even motivating them to pursue and eventually obtain the answer. We highlight some other future directions in TOT research, such as focusing on TOTs in people with anomia.

The TOT state shares characteristics and empirical patterns with many other cognitive phenomena. Among these shared characteristics are resolution patterns, as in the case of creative problem-solving and the factors that both hinder and contribute to resolution in that domain, and the feeling of closeness that characterizes many subjective metacognitive states (including presque vu, curiosity, familiarity sensations and feelings of knowing). Finally, the TOT state appears to be related to the notion of internally directed cognition, possibly as a window onto how attentional processes are modulated to focus inward vs. outward. Continuing to research the TOT phenomenon could shed important light on broader issues of human cognition, including mechanisms of creative thought, attentional modulation, and the basis of subjective states of awareness in metacognition.

This book is a scientific discussion of tip-of-the-tongue (TOT) states. First, the TOT state is a subjective experience – a feeling. Second, the feeling is about retrieval. The TOT state is a feeling that we can or will remember something. Brown and McNeill (1966) introduced the term “prospecting” into the language of TOT state research, which meant presenting rare-word definitions to participants and asking them to identify the word for each, and when unable to do so, assessing if they were in a TOT state for it. Brown and McNeill showed that TOTs can be captured in the lab, and that TOTs are accurate at predicting later memory performance. They set the stage for the next fifty-plus years of research on TOTs. Subsequent models focused on both how retrieval breaks down during a TOT state and what causes the subjective experience of a TOT state.

This chapter covers the various theorized causes of TOT states put forward over the years. The direct-access approach postulates that TOT states are caused by privileged access to the strength of a word’s representation in memory. Several models have been advanced to account for TOT states using this approach. We review the Transmission Deficit Model and a more general “Two-Step” model approach, followed by a review of the Interactive Competition Activation (IAC) model of TOT states for people’s names in response to seeing their faces. The inferential approach postulates that TOT states are caused by a number of accessible heuristic cues and clues, such as the familiarity or fluency of the cue or cues in the environment, and the presence, quantity, or fluency of perceived partial target or retrieved related information. The metacognitive-heuristic model predicts TOT states based on the accumulation of heuristic information. We also review some alternative theoretical approaches worthy of noting: blocking theory and our newly put forward possibility that TOT states can potentially result from unresolved competition among candidate word representations.

TOT states are a common experience across all human beings regardless of age, language, culture, or ethnicity. Furthermore, there is overlap between our technical use of the term “tip of the tongue” and the everyday usage of the phrase and its accessibility to people regarding what it means when it is described to them. The universality of the experience makes the TOT state an ideal window onto human consciousness. Other “tip-ofs” exist too. The tip-of-the-finger phenomenon refers to the experience that sign-language users have when they are sure that they know a hand sign for a word but cannot retrieve it. The tip-of-the-nose phenomenon refers to the experience that one knows a particular odor but cannot retrieve the name for it in that moment. The tip-of-the-pen phenomenon refers to the experience among readers of Chinese languages of being able to recall the word but not being able to recall the character that represents that word in written Chinese. From diary studies, we know that most real-world TOT states are for proper names, that most naturally occurring TOT states are resolved, and that TOT states increase in frequency with age.

Although TOT states are commonly viewed as negative experiences and although the TOT-related biases reviewed in the previous chapter might suggest that TOT states carry with them additional detrimental consequences beyond any frustration in being unable to recall a word, the research reviewed in this chapter paints a different picture. This research suggests that TOT-related biases often lead to useful behaviors that not only can increase both the likelihood and speed of TOT resolution, but can be capitalized on in the right circumstances to advance and increase human potential.

TOT states have a subjective phenomenology to them that is worthy of investigation in and of itself. Although examining the mechanisms of word-retrieval failure is an important part of fully understanding TOT experiences, the mechanisms of word-retrieval failure are not the complete picture. For one thing, not all instances of word-retrieval failure result in a TOT state. For another, TOT states are an inherently subjective phenomenon with a potentially unique set of phenomenological qualities that distinguish them from other metacognitive states of awareness and experiences. Understanding the subjective phenomenology of TOTs could help to elucidate important facets of metacognition as well as human consciousness more broadly.

One of the most replicated findings about TOT states is that older adults experience more TOT states than younger adults. We argue that young children also experience TOT states, and that younger children, at least as young as six years old, experience more TOT states than do older adults. These results are consistent with both theoretical approaches – direct-access theories that propose that TOT states arise from failures in word retrieval as well as metacognitive models in which TOT states arise from heuristic cues and clues about that retrieval. In the direct-access word-retrieval approach, the younger children and the older adults are said to have weaker connections between semantic and phonological nodes, leading to more retrieval failures and therefore more TOT states. In the metacognitive model, older children and older adults apply a more complete set of heuristics to determine whether a TOT state is present when word retrieval fails, thus leading to more accurate TOT states. Delineation of these models requires further work.