Language is fundamental for successful human communication, whose execution relies on access to the necessary data in the mental lexicon. The mental lexicon is a storage or structure which contains linguistic information. Words are stored in the mental lexicon as wholes consisting of stems and appropriate affixes. Before speaking, a speaker must first choose the most suitable word in a particular context, which leads to the activation of other similar words and the competition among them. The “tip-of-the-tongue” phenomenon, illustrated in the second main body chapter, is a state described as the unability to recall a word which is usually known to a person; however, they can remember other words, similar in structure and meaning. The mechanics of speech production were examined and explained through a number of models, two of which are analysed in this thesis. The first one, Levelt's model of speech production, argues that language is produced in three phases: conceptualization, formulation and articulation, all of which are part of the same processing system. On the other hand, Paivio's Dual coding theory assumes that language is produced as a result of verbal and nonverbal processing systems, which are functionally independent and interconnected. In Dual coding theory, representational units of the verbal processing system are called imagens, while logogens are the representational units belonging to the nonverbal processing system.