What does the mean length of utterance (MLU) primarily index in child language development?

What does the mean length of utterance (MLU) primarily index in child language development?

• A. The average number of morphemes per utterance, used to index syntactic complexity and developmental stage.
• B. The total number of words produced per day.
• C. The number of different verbs a child uses.
• D. The length of the child's longest utterance.

Answer: (A)

MLU primarily indexes the syntactic complexity of a child’s speech by averaging the number of morphemes per utterance. A morpheme is the smallest unit of meaning, including free units like cat or dog and bound units like -ing, -ed, -s, or -'s. As children acquire more grammatical endings and function words, their utterances tend to include more morphemes, so the mean length in morphemes grows. This makes MLU a useful rough indicator of developmental stage in syntax during early language. The total number of words produced per day isn’t the focus of MLU, and MLU emphasizes structural complexity over lexical variety. Likewise, counting the number of different verbs or the length of the longest utterance does not capture how sentences are being built and expanded across a speech sample.

MLU primarily indexes the syntactic complexity of a child’s speech by averaging the number of morphemes per utterance. A morpheme is the smallest unit of meaning, including free units like cat or dog and bound units like -ing, -ed, -s, or -'s. As children acquire more grammatical endings and function words, their utterances tend to include more morphemes, so the mean length in morphemes grows. This makes MLU a useful rough indicator of developmental stage in syntax during early language.

The total number of words produced per day isn’t the focus of MLU, and MLU emphasizes structural complexity over lexical variety. Likewise, counting the number of different verbs or the length of the longest utterance does not capture how sentences are being built and expanded across a speech sample.