MLU (Mean Length of Utterance)

Summary

This video explains the concept of Mean Length of Utterance (MLU) as a measure of grammatical development in toddlers, introduced by Roger Brown and his colleagues. While MLU has become a widespread tool in research and clinical practice, the video critiques its limitations, particularly for young toddlers. By analyzing four toddler utterances of equal length but varying grammatical complexity, the script highlights how MLU fails to account for the hierarchical nature of language. The video suggests that alternative methods are needed to measure grammatical development more accurately, inviting viewers to explore these tools in future content.

Takeaways

• 😀 Roger Brown and colleagues studied grammatical development in toddlers by analyzing language samples.
• 😀 They focused on the acquisition of closed-class words and morphemes crucial to English grammar.
• 😀 To measure grammatical growth, they introduced the concept of Mean Length of Utterance (MLU).
• 😀 MLU became widely used in both research and clinical practice as a measure of grammatical development.
• 😀 Despite its popularity, many researchers question MLU's effectiveness, especially for young toddlers.
• 😀 Four toddler utterances, each with three morphemes, illustrate how MLU fails to capture differences in grammatical complexity.
• 😀 The utterance 'Oh, bye, baby' is three words but lacks grammatical structure, acting as separate word islands.
• 😀 The utterance 'two eyes' forms a noun phrase, with the number preceding the noun and a plural morpheme.
• 😀 The utterance 'on his head' is a more complex prepositional phrase, with a noun phrase within it.
• 😀 The utterance 'you dry it' is a subject-verb-object sentence, the most complex of the four examples.
• 😀 MLU overlooks the hierarchical nature of language, failing to capture the true complexity of grammatical development.
• 😀 Researchers are exploring alternative methods to assess grammatical development in toddlers beyond MLU.

Q & A

What is the concept of 'Mean Length of Utterance' (MLU)?

Mean Length of Utterance (MLU) refers to the average number of morphemes in a toddler's utterance. It is used as a measure of grammatical growth, with the idea that longer utterances indicate more complex language development.

Why is MLU considered an important tool in language development research?

MLU is important because it provides a simple and quantifiable measure of a toddler's grammatical development. It has become widely used in both research and clinical practice to track language milestones.

What is a limitation of using MLU as the sole measure of grammatical development?

One limitation of MLU is that it does not account for the grammatical complexity of different utterances. For example, utterances with the same number of morphemes may differ significantly in their grammatical structures.

How does MLU treat utterances with the same number of morphemes?

MLU treats utterances with the same number of morphemes as equivalent, regardless of their grammatical complexity. This can lead to oversimplification, as some utterances may be more syntactically complex than others despite having the same length.

What is an example of a grammatically simple utterance in the script?

'Oh, bye, baby' is an example of a grammatically simple utterance. Although it contains three words, it lacks syntactic complexity and does not form a structured phrase.

How is 'two eyes' grammatically different from 'Oh, bye, baby'?

'Two eyes' is a noun phrase with a number preceding the noun, following English grammar rules. While it has three morphemes, it is a more structured phrase compared to 'Oh, bye, baby'.

What makes 'on his head' a more complex utterance than 'two eyes'?

'On his head' is a prepositional phrase with a noun phrase ('his head') inside it. This hierarchical structure makes it more complex than 'two eyes', which is a simpler noun phrase.

Why is 'you dry it' the most complex structure among the four examples?

'You dry it' is a sentence with a subject noun phrase ('you'), a verb phrase ('dry it'), and a direct object noun phrase ('it'). As a complete sentence with an SVO structure, it is more syntactically complex than the other utterances.

What does the script suggest about the hierarchical nature of language?

The script emphasizes that language is not organized linearly but hierarchically. Words combine to form phrases, and phrases combine to form sentences, which adds to the complexity of grammatical development.

What alternative methods are being researched for assessing grammatical development in toddlers?

The script mentions that researchers are exploring alternative tools for assessing grammatical development in toddlers, beyond MLU, to better capture the complexity of their language growth.