The Tip-of-the-Tongue phenomenon: Who, what, and why

The process of speech production occurs relatively effortlessly, despite complex cognitive processes that underlie word retrieval. However, sometimes these processes do break down and result in a production failure called a tip-of-the-tongue (TOT) state. TOTs are temporary wordfinding problems, characterized by an inability to retrieve a word at an intended time despite a strong feeling of knowing the word. TOTs are of particular relevance to older adults, who report having more TOTs and rate them as their most frustrating cognitive failure. The present chapter reviews the relevant literature on age-related changes observed in the TOT phenomenon, with a specific investigation of factors that increase the likelihood of older adults having TOTs as well as those that promote or inhibit TOT resolution. We begin by defining TOTs and their underlying causes in the context of theories of language production. We then discuss empirical findings that examine older adults' disproportionate vulnerability in experiencing TOTs, the ways in which the incidence and resolution of TOTs can be exacerbated or mitigated, the particular susceptibility of proper names to TOTs, and comparisons of healthy older adults with adults with some clinical memory disorders. The chapter concludes with a brief discussion of suggestions for future research directions that may shed light on other unique contributors to these language production failures in old age. Tip-of-the-Tongue (TOT) Phenomenon 3 The Tip-of-the-Tongue Phenomenon: Who, What, and Why In the course of conversation, almost all speakers, irrespective of variables like age or native language, have experienced a tip-of-the-tongue (TOT) state, which represents a temporary and often frustrating inability to retrieve an intended word (e.g., Burke, MacKay, Worthley, & Wade, 1991; Burke & Shafto, 2004; Gollan, Ferreira, Cera, & Flett, 2014; Gollan, Montoya, & Bonnani, 2005; Miozzo & Caramazza, 1997). Even people who use sign language, whether hearing-impaired or not, experience language production failures in the form of "tip-of-thefingers" (Pyers, Gollan, & Emmorey, 2009; Thompson, Emmorey, & Gollan, 2005), and speakers of logographic writing systems like Chinese can temporarily forget the visual representation of a character, resulting in a "tip-of-the-pen" experience (see Brown, 2012, for a review). The ubiquity of this experience, along with a noticeable increase in TOTs that accompanies normal aging, has made this phenomenon the focus of numerous research studies. What is a TOT, and why does it occur? One of the earliest known references for describing a TOT, without using the term itself, is James (1893), who summarized the experience as follows: Suppose we try to recall a forgotten name. The state of our consciousness is peculiar. There is a gap therein; but no mere gap. It is a gap that is intensely active. A sort of wraith of the name is in it, beckoning us in a given direction, making us at moments tingle with the sense of our closeness and then letting us sink back without the longed-for term. If wrong names are proposed to us, this singularly definite gap acts immediately so as to negate them. They do not fit the mould. And the gap of one word does not feel like the gap of another, all empty of content as both might seem necessarily to be when described as gaps (p.251). Tip-of-the-Tongue (TOT) Phenomenon 4 Laboratory research on TOTs did not begin until more than 70 years later, with Brown and McNeill's (1966) seminal empirical study, where they developed a methodology of inducing TOTs in a laboratory setting. They presented definitions whose answers corresponded to a lowfrequency word (e.g., ambergris) and asked participants to try and recall the word. Participants who experienced a TOT were asked to record various characteristics of the TOT word, including the number of syllables, first letter, and words with similar sound or meaning. They found that people reported TOTs (360 instances for 56 participants, each of whom heard 49 definitions), which were often accompanied by the retrieval of partial information even when the word itself could not be retrieved. These results documented TOTs as a reliable phenomenon that could effectively be produced in the laboratory and quantified aspects of the TOT state, contributions that were invaluable for subsequent research (see also Brown, 2012, for a historical review). Early theories about the etiology of TOTs proposed an inhibition explanation, in which TOTs result from a more accessible, alternative word (i.e., interloper) coming to mind first and subsequently blocking retrieval of the intended word (e.g., Brown, 1979; Jones, 1989; Jones & Langford, 1987; Reason & Lucas, 1984; Roediger, 1974; Woodworth, 1929). Some studies provided support for this hypothesis by showing that TOTs could be increased following presentation of a word that was phonologically related (i.e., sharing sounds) to the TOT word. For example, presentation of the word dissociation resulted in more TOTs when participants were trying to retrieve diminuendo compared to when an unrelated word was presented (e.g., Jones, 1989; Jones & Langford, 1987; see also Maylor, 1990a). However, subsequent research revealed methodological problems with some of these studies (e.g., improper counterbalancing such that questions preceded by a phonologically related word were more difficult to answer and Tip-of-the-Tongue (TOT) Phenomenon 5 therefore inherently more prone to TOTs; Meyer & Bock, 1992; Perfect & Hanley, 1992), and ultimately there was little empirical support for blocking as the cause of TOTs. Alternatively, the cause of TOTs has been specified within theories of speech production. Although theories differ, they generally agree that speakers must complete several stages of processing before articulation of a word begins and results in successful speech production. Specifically, the speaker first chooses the underlying concept to be expressed, then undergoes the process of lexical selection by choosing an abstract word (lemma) that best reflects the concept's meaning and specifies the appropriate syntactic properties, such as its grammatical class. Once selected, the lemma undergoes phonological encoding by transmitting activation to the word's phonology, e.g., syllables and phonemes, so that the word can be articulated. TOTs are thought to involve a breakdown between lexical selection and phonological encoding, where lemma selection was completed successfully, but phonological encoding of the lemma was not (e.g., Burke et al., 1991; Dell, 1986; Levelt, 1989; but see Caramazza & Miozzo, 1997). Retrieval of partial information, as demonstrated by Brown and McNeill (1966), shows that phonological encoding can be partially completed, giving a speaker access to some of the TOT word’s phonological information, such as its first letter/phoneme or number of syllables. To produce the word, however, phonological encoding of the lemma must be completed in its entirety. This breakdown between lexical selection and phonological encoding seems to be exacerbated in old age, evidenced by older adults experiencing more TOTs than young adults, both in self-report diaries and experimental settings (e.g., Brown & Nix, 1996; Burke, Locantore, Austin, & Chae, 2004; Burke et al., 1991; Maylor, 1990b, 1997; Salthouse & Mandell, 2013). In fact, TOTs are often cited as one of the most commonly experienced memory problems, with TOTs for proper names as older adults' most troubling cognitive problem (Cohen & Burke, 1993; Tip-of-the-Tongue (TOT) Phenomenon 6 Cohen & Faulkner, 1986; Lovelace & Twohig, 1990; Ossher, Flegal, & Lustig, 2013; Sunderland, Watts, Baddeley, & Harris, 1986). Understanding why TOTs increase with normal aging is important for several reasons. One is that it can help to discriminate between healthy and pathological aging. Knowing what is a "normal" amount of TOTs for a given age range can help us to better understand when older adults' memory failures are typical or whether they may be an indicator of pathological declines associated with advancing age, such as Alzheimer's disease (AD) or mild cognitive impairment (MCI). In fact, naming difficulties have been identified as among the most functionally debilitative consequences of dementias (Croot, 2009; Gonzalez Rothi et al., 2009; Reilly, Martin, & Grossman, 2005). Another reason is that even in healthy aging, experiencing TOTs has important social consequences. Older adults may withdraw from social interactions if they feel like their TOTs are disrupting conversations or creating a perception of incompetence (e.g., Cohen, 1994; James & Burke, 2000). Thus, an understanding of TOTs is also critical for helping older adults to maintain social and communicative