1 Comprehension and production

Many researchers and parents have noticed that children, especially early on in their development, comprehend more language than they produce, referred to as the comprehension-production asymmetry. Across many different languages children understand more words, meanings, morphology and grammar, before they produce them. The fact that language comprehension and production dissociate like this suggests they are affected by different factors in development (see Figure 1).

Figure 1 The comprehension-production asymmetry in vocabulary development. Each dot represents data from an individual child learning English. If children were equally able to produce as many words as they understood, then the dots would line up on the diagonal. In fact, children cluster towards the bottom of the graph showing that comprehension emerges before production in development.

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A graph showing the connections between total words produced and total words understood.

Figure 1 The comprehension-production asymmetry in vocabulary development. Each dot represents data from an individual child learning ...

Acquiring some skills like riding a bike are judged on their performance. We don’t need to understand why someone else is riding a bike before we can ride one ourselves. Language is different. Comprehending why someone else is using a piece of language is crucial when learning to produce that piece of language ourselves. This is because there are certain norms that are shared between speakers about what words and phrases to use in certain contexts (think back to Session 2). Until children have some understanding of language, their ability to use it properly is limited, which is one reason we see a comprehension-production asymmetry. There are other reasons we see this gap. Producing speech or gestures requires significant cognitive effort, such as memory retrieval, planning, motor control (which you learned about in Session 3), and those abilities often develop later than the ability to recognise words.