The tip-of-the-tongue (TOT) phenomenon is that frustrating experience when you feel you know a word, answer to a question, etc. but just can’t seem to get it out. In other words, it is when information that is stored in memory is not readily accessible. Many times, individuals experiencing this phenomenon can recall the first letter, length of the word, or approximate the sound of syllables in the word. However, despite feeling retrieval from memory is imminent, the full word or bit of information is still not fully available for recall. TOT is affected by various factors such as emotional content (retrieval takes longer if the memory is more emotional), age, and bilingualism and others. There are two general theories for why TOT occurs. One is the direct access view, which is one of memory strength. Essentially there is a memory for the item that is strong enough to trigger TOT but not strong enough to retrieve the word. The inferential view suggest that TOTs are caused by clues that an individual can remember and piece together to infer the target word.
Brown, R., McNeill, D. (1966). The “tip of the tongue” phenomenon. Journal of Verbal Learning and Verbal Behavior, 5, 325-337.
Brown, A.S. (1993). A review of the tip-of-the-tongue experience. Psychol Bull., 109, 204-223.