Reading span task is like a game that helps scientists understand how well you can remember letters and understand sentences at the same time.
Imagine you are playing a game with a teacher or a scientist who gives you a list of letters to remember, like A, T, E, and F. Then, they say a sentence like "The cat sat on the mat." You have to remember the letters and also understand the sentence at the same time.
After they say a few more sentences, they ask you to repeat the letters you remember in order. If you can remember all of them, that's great! You have a high reading span. If you can't remember them all, that's okay too. It just means your reading span is lower.
This game helps scientists understand how our brains process both language comprehension and memory at the same time.