Tip-of-the-Tongue States Yield Language Insights

Probing the recall of those missing words provides a glimpse of how we turn thoughts into speech and how this process changes with age

Lise Abrams

The Processes of Speaking

What causes a TOT state in the first place? To answer that question, we must understand how speech is produced. On average, people talk at a rate of about two to four words per second and make an error every 1,000 words or so. The rarity of errors is remarkable, given the complex, albeit unconscious, mental gymnastics that translate a concept into spoken words.

These cognitive processes begin with a nonverbal message, a general idea of what the speaker plans to say. This step is followed by a second process, called lexical access, in which a word or words are chosen to carry the message. During lexical access, language centers in the brain select a lemma, a lexical representation that is consistent with the meaning (semantics) of the word to be expressed and contains its grammatical (syntax) properties. Following lemma selection, the brain retrieves the neural blueprints for the sounds that make up the word (its phonology) and sends those plans to the system that directs speech articulation. Muscles in the mouth, throat and diaphragm work together to produce speech.

The stage for retrieving semantics and syntax is separate from the one for retrieving phonology, but debate continues about how these stages interact. According to "stage" or "discrete" theories of speech production, the stages are independent of one another. Discrete theories emphasize sequence: a lemma must be selected before phonological encoding. Alternatively, "interactive activation" theories of speech production say the cognitive processes for lemma selection and phonological encoding somehow communicate back and forth. In other words, interactive activation theories allow phonological processing to influence lemma selection; discrete theories rule out this possibility.

Both types of theories agree that TOT states arise when the brain selects the appropriate lemma but fails to encode its phonology. Because lemma selection has already happened, TOT states are marked by a strong "feeling of knowing"—we know we know the word. For example, when I see a student whom I taught several semesters ago, I typically cannot retrieve her name (although I will recognize it once she says it). But I can often remember other information about her—what she looked like, where she sat in the classroom, whether she was a good student. With respect to phonological encoding, an incomplete retrieval might lead us to recall the first letter of the word or its number of syllables. But to retrieve the whole word, its entire phonology must be available and fully encoded. Failure in the latter process causes a TOT state.

Our internal representations of words are housed in semantic and phonological systems. The semantic system contains all of our knowledge about word meanings, and the phonological system contains the words' sounds. Figure 3 shows the word marsupial broken down into its syllables and corresponding sounds, or phonemes. Solid lines in the figure represent the fact that retrieving semantic knowledge about words is usually easy; we tend not to forget the meanings of words in our vocabulary. Dotted lines indicate the weak connections between the word and its sounds, and those weak connections are the cause of TOT states.

Why do connections between words and their phonology weaken? Two cognitive psychologists, Deborah M. Burke of Pomona College and Donald G. MacKay of the University of California, Los Angeles, proposed the "transmission deficit model" of TOT states, which suggests three main causes. One is low frequency of use: Words used infrequently have weaker connections to their sounds, which is why TOT states typically occur for relatively rare words such as marsupial. A second cause is nonrecent use: A word not accessed recently will also have weaker connections. For example, the names of people we haven't seen or talked to in a while, such as our fourth-grade teacher, are more susceptible to TOT states. The third cause is normal aging: As we get older, all connections between words and sounds weaken independently of the other factors.