Cognitive Psychology · Simplified
Working-Memory Load Laboratory
Holding things in mind is not one resource being used up. What it costs depends on what else you are doing with it.
Practice
Hold the letters, do the other thing, then recall
Each trial has three parts. You are shown some letters to hold in mind. Then you make four quick judgements about something else. Then you pick the letters out of a grid. Two practice trials first.
What this needs. About five minutes, and no writing anything down: holding the letters in your head is the whole point. The in-between judgements are paced and will move on without you, which is deliberate, but nothing else is ever timed out.
What it cost
Not one pot of resources
Two lines, one for each kind of in-between task. If holding letters and doing something else drew on one single pool, the two lines would fall together. If the cost depends on what the something else is made of, they come apart.
All the values behind this chart
| In between | Letters held | Letters recalled | Trials |
|---|
Key idea: Both in-between tasks are easy, both take the same time, and both keep you busy. If working memory were a single pot of effort, it would not matter which one you did: any distraction would cost the same. It usually does matter. Holding letters and judging letters both need whatever it is that handles verbal material, so they compete directly. Holding letters and judging positions compete much less, because the second one is not made of the same stuff. That is the evidence behind the idea that working memory has separable parts rather than one general-purpose store, and it is why the two lines coming apart is more informative than either line on its own.
One person, a handful of trials per cell, so each point is rough and the two lines can easily cross the wrong way by chance. The two in-between tasks are matched for pacing and number of judgements but not for difficulty, so part of any difference could be that one is simply harder rather than that it shares a domain; a properly matched pair is difficult to build and this one is not it. Nothing here measures anyone's memory span or ability, and a flat pair of lines is a result about the block rather than about you.
The longer version adds a third load level, practice trials with explanatory feedback on every one, and a fuller treatment of what separable parts does and does not mean. It is at Working-Memory Load Laboratory in the main collection.