Nadia has been on the job for two weeks. Her team lead walks with her to the printer and says in passing: 'Oh, when you create a customer you first need to check whether they are already in the old system, then copy the registration number, and do not forget the invoicing checkbox, otherwise the invoice goes to the wrong address.' Nadia nods. Back at her desk she remembers there was something about a checkbox. The rest is gone.
She could have written it down. She knows that too. But in the moment it seemed manageable, and besides, in your second week you do not want to give the impression that you cannot remember a simple explanation.
A small workbench
In 1974 Alan Baddeley and Graham Hitch proposed a model of what they called working memory. The idea is that your brain has a small workbench on which you hold and process information for a few seconds: keeping a phone number in mind until you have dialled it, doing a sum in your head, understanding a sentence while you hear it. In their model there are separate components for sound (what you hear or say to yourself) and for images, with a kind of conductor above them that distributes attention.
That workbench is small in everyone. Exactly how small has been debated for years. In 2001 Nelson Cowan concluded, after a large analysis, that adults can hold about four separate items at once on average, if they do not use tricks such as repeating or grouping. Four. The instruction at the printer had at least five.
What is different in ADHD
In ADHD, working memory is one of the best-studied weak spots. In 2012 Lisa Kasper, Matt Alderson and Kristen Hudec pooled 45 studies in children and found large differences from peers, both for words and sounds and for images and positions. A year later the same group did it again for adults, with 38 studies. There the differences were moderate in size, but clearly present. So people do not grow out of this. At most it gets somewhat smaller, and adults learn to work around it.
Two things matter here. First, these are averages. There are people with ADHD with perfectly good working memory, and people without ADHD with poor working memory. Second, working memory in ADHD is smaller and also more erratic. It works better when something is interesting and worse when attention slides away, which ties in with what we describe in the other articles in this series.
Why long explanations vanish
In 1988 the educational psychologist John Sweller described what happens when a task swallows working memory whole. He had people solve puzzles and saw that those who needed all their capacity to crack the puzzle learned little from it afterwards. All the working memory went into searching; nothing was left to remember the pattern. Out of this grew cognitive load theory: learning fails when the way information is presented demands more working memory than there is.
Spoken instructions are the textbook example. Speech is fleeting. While you hear step two, you have to hold step one, and by step three you have to keep all three and also work out whether you have a question. With a workbench of four slots, that is already full. With a workbench that works erratically, something drops off along the way, and it is usually not the last thing you heard.
Long documents do something similar, in a different way. A forty-page handbook asks you to remember where you are, how this chapter relates to the previous one, what the abbreviations meant and what you will have to do with it later. That bookkeeping occupies the workbench before the content even fits on it.
Richard Mayer and Roxana Moreno studied how to solve this. In 2003 they listed nine ways to reduce the load. One of them is segmenting: presenting the same explanation in small pieces, where the reader or viewer starts the next piece themselves. In an earlier experiment by Mayer and Chandler, students watched an animation about how lightning forms, either in one go or in sixteen pieces of eight to ten seconds with a 'continue' button. Those who got the pieces were better at applying what they had learned. The content was identical. Only the portion size differed.
Small portions are for everyone
There is a misconception that presenting information in small steps is for people who would not get it otherwise. The research says something else. Everyone's working memory is small, and the way information is presented decides how much of it reaches the content. For people with ADHD the difference is bigger, because their workbench is smaller and more erratic. But the colleague without ADHD who was thinking about her three o'clock meeting during the explanation at the printer has lost that instruction too.