Bottom-up processing happens when someone tries to understand language by looking at individual meanings or grammatical characteristics of the most basic units of the text, (e.g. sounds for a listening or words for a reading), and moves from these to trying to understand the whole text. Bottom-up processing is not thought to be a very efficient way to approach a text initially, and is often contrasted with top-down processing, which is thought to be more efficient.
Asking learners to read aloud may encourage bottom-up processing because they focus on word forms, not meaning.
In the classroom
Learners can be encouraged to use both bottom-up and top-down strategies to help them understand a text. For example in a reading comprehension learners use their knowledge of the genre to predict what will be in the text (top-down), and their understanding of affixation to guess meaning (bottom-up).