[Lexical development. The construction of different vocabulary tests used in clinical practice]

During first language acquisition (L1), children need to gather knowledge about the speech sounds and grammar of their mother tongue. Furthermore, communication skills require an adequate vocabulary. Individual profiles of vocabulary acquisition can vary considerably. However, actively using around 50 words by the age of 24 months is considered a milestone in first language acquisition. This is usually followed by the so-called vocabulary spurt, a rapid increase in lexical knowledge. This article provides an overview of the theories of lexical development and discusses how the acquisition of vocabulary may be explained.

A selective literature search was conducted in PubMed and Scopus. Current textbooks were also considered.

In order to acquire new words, a child has to identify what the new string of speech sounds refers to. The child has to construct a valid concept of the word and subsequently store both word and concept into long-term memory. Several theories have been put forward to explain lexicon organization, the acquisition of concepts and the mechanisms underlying the so-called fast mapping phenomenon in particular. All of these attempt to explain the phenomenon of lexicon acquisition in terms of a model scheme. In the context of the fast mapping mechanism, constraints and assumptions, cognitive, intentionalist and emergence-based theories are discussed.

Knowledge of the different theories of vocabulary acquisition is mandatory to understand the construction of the tests used to assess vocabulary skills in clinical practice and to apply these appropriately.