We’ve all experienced what the cartoon character has just gone through. You decide to do something the next time you go into a room where that task has to be done and then as soon as you get there, you forget what it was that you wanted to do. Sometimes you know that you have forgotten something but can’t recall what it is, at other times you don’t even realize that you have forgotten until much later, when you are doing something else.

This is because the brain can only store so much stuff in its working memory and has to throw stuff out that it thinks are no longer needed.

Capacity is limited – we can keep only a certain amount of information “in mind” at any one time. But researchers debate the nature of this limit.

Many suggest that working memory can store a limited number of “items” or “chunks” of information. These could be digits, letters, words or other units. Research has shown that the number of bits that can be held in memory can depend on the type of item – flavors of ice cream on offer versus digits of pi.

But why does loss of memory happen more frequently when we go into another room? If you are older like me, you may dismiss these as ‘senior moments’ but it turns out that age has little to do with it, that forgetting such things is simply due to moving to another room.

Participants traversed a real-world environment, carrying physical objects and setting them down on actual tables. The objects were carried in shoeboxes to keep participants from peeking during the quizzes, but otherwise the procedure was more or less the same as in virtual reality. Sure enough, the doorway effect revealed itself: Memory was worse after passing through a doorway than after walking the same distance within a single room.

Experimenters have found that it is not the distance moved that is the problem. Moving a similar distance within the same room did not cause as much memory loss as moving that distance but into another room. It is also not the case that a different room by itself causes the problem because if participants moved into another room and then back into the original room, they still tended to forget. It seemed as if the act of moving through a doorway caused the forgetting and thus the name given to it, the ‘doorway effect’.

The authors of these doorway studies speculate that it is costly to keep things in one’s working memory and that the brain uses various cues to decide what to keep and what to throw out.

The doorway effect suggests that there’s more to the remembering than just what you paid attention to, when it happened, and how hard you tried. Instead, some forms of memory seem to be optimized to keep information ready-to-hand until its shelf life expires, and then purge that information in favor of new stuff. Radvansky and colleagues call this sort of memory representation an “event model,” and propose that walking through a doorway is a good time to purge your event models because whatever happened in the old room is likely to become less relevant now that you have changed venues. That thing in the box? Oh, that’s from what I was doing before I got here; we can forget all about that. Other changes may induce a purge as well: A friend knocks on the door, you finish the task you were working on, or your computer battery runs down and you have to plug in to recharge.

Why would we have a memory system set up to forget things as soon as we finish one thing and move on to another? Because we can’t keep everything ready-to-hand, and most of the time the system functions beautifully. It’s the failures of the system – and data from the lab – that give us a completely new idea of how the system works.

You can read the studies here and here.

Recently, I decided look into getting long-term care insurance for myself because it can be expensive. The insurance company told me that I had to be interviewed over the phone and that it would also involve tests of cognitive ability. I think that if you already show signs of cognitive decline, they are unlikely to insure you. During the tests, the interviewer said that she would give a list of ten ordinary items (knee, carpet, bird, etc.) and ask me to say them aloud in a sentence. Then later in the interview she would ask me to recall as many of the words as I could. This was clearly on the honor system since it was a phone interview and I could have written the words down. I did not do that of course nor did I use any of the many mental tricks that one can use to remember lists of things, since that would also violate the spirit of the test. I was curious as to how well I would do. I ended up remembering six items easily and another two with difficulty and two not at all. This must have been sufficient since they offered me the policy anyway.

So as far as the insurance company is concerned, I am not as yet showing signs of losing my marbles, which is good to know.