prospective memory

Forgetting to do things

  • Forgetting future tasks and events is the most common type of memory failure
  • Older adults are in general no worse at this type of remembering than younger adults
  • Older adults may have more difficulty at remembering to do actions at particular times
  • Older adults also need to make more effort in situations when an action cannot be performed immediately, but must be held in memory for a brief period.

The other day I was sitting in the sunshine in my living room going through some journal articles I'd photocopied. I realized I needed to staple the pages together and went down to my study to get the stapler. Approaching my desk, I decided to check my email while I was there. And then, I decided to check my library account online to see whether a book I had requested had turned up. When I'd done that, I went back upstairs to my papers. Where I realized, of course, that I'd forgotten the stapler.

This type of memory failure — going to do something, getting sidetracked, doing something else and forgetting the original task — is familiar to all of us. As are everyday memory failures like forgetting to put the garbage out; forgetting to take medication at the right time; forgetting a dentist appointment (although there's more than one reason for that!).

This type of memory failure — forgetting the future, as it were — is a failure of a type of memory called prospective memory, and it is probably the most common type of memory failure older adults suffer from. And probably the biggest concern.

It's a concern because it's a failure of memory that has consequences, and those consequences are often not only obvious to ourselves, but also to others. Which makes us feel worse, of course.

But it's not just a matter of being embarrassed. Older adults are particularly vulnerable to thoughts that they are "losing" their memory — and the fear of Alzheimer's lurks in all of us.

So, should you be worried if you forget what you're doing?

Like other types of forgetting or absent-mindedness, it depends on the degree of your forgetfulness. But prospective memory failure is common among older adults for a very good reason. Not because it's a precursor of cognitive impairment, but because it's the most common type of memory failure for everyone.

In fact, older adults in general are no worse than anyone else in this particular memory domain, although they may worry about it more (because they worry about any memory failure more).

In some aspects of prospective memory, older adults are actually better than younger adults! One reason for this is that they are more likely to use memory aids — like writing down reminders, or putting reminder objects in strategic places — to help them remember.

However, it does seem that older adults may do less well at remembering things that have to be done at particular times, and one reason for this seems to be that they tend to be poorer at monitoring time. In these cases, it's therefore a good idea to use timers as reminders.

Older adults also seem to have more trouble in the situation when a remembered intention cannot be performed immediately, but must be held in memory for a brief period. Even 5-10 seconds is too long! Tasks that you are "just about" to perform, but in fact are not doing that very second (because you have some other intervening task to do first) are probably particularly dangerous because you don't feel a need to make an effort to remember them (because you are "just about" to do it). But without rehearsal, information falls out of working memory (the stuff we're holding in the conscious "forefront" of our mind) in seconds. So you do need to make an effort. And often, that's all it needs.

You can read more about planning memory strategies in my ebook on planning memory.


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Action Slips

There is a very common form of forgetfulness that is not really a failure of memory. When we get in our car to drive to place A and find ourselves instead on the road to the more familiar place B, this is not a failure of memory. When we clear the table and find ourselves putting the margarine in the dishwasher or the dirty plate in the fridge, this is not a failure of memory. When we go into a room intending to do one thing and do something else instead, this is not, really, a failure of memory.

These are absentminded errors, and they happen to all of us. They have also been termed action slips, and this term is useful because it points more precisely to the nature of these errors. Let's look at the characteristics of action slips:

  • they usually occur during the performance of tasks that are so highly practised they are largely automatic
  • they usually occur when we are preoccupied or distracted
  • many involve intrusions of other habitual actions that share some characteristics with the intended action
  • such habit intrusions are more likely to occur when:
    • we're departing in some way from our usual routine (for example, you decide to stop adding milk and sugar to your coffee, then finding yourself doing it automatically)
    • the situation has changed, demanding a change in our usual routine (for example, a much-visited shop moves premises, but you keep going to its old location)
    • the situation shares features with a highly familiar situation (for example, you try and open a friend's car with your own car key)

Other types of action slips are:

  • place-losing errors - where you've lost your "place" in an action sequence, and so omit or repeat part of the sequence (for example, because of wheat sensitivities in my family, I make our own bread; accordingly, it is a highly practiced recipe, and I add all the ingredients in a fixed order. If something happens to distract me in the course of it, I may be unsure where I am in the sequence, and risk omitting or repeating an ingredient)
  • blends - where you get confused between two active tasks (for example, you write an email while thinking about the next email you're going to write, and address the current email to the correspondent for the second email)
  • reversals - where you get confused between parts of the same task (for example, you put an empty ice cube tray in the freezer, then turn to the tap to fill it)

You can see from all this that these everyday errors occur in the context of action sequences - that is, sequences of actions that we have practised so often they have become automatic. Dressing, undressing, washing, making coffee or tea, even making quite complicated recipes - these are all common examples of action sequences.

You can see why action slip is therefore a good name for these types of error.

Is there anything we can do to minimize action slips? Well, the standard advice is to pay attention to what you're doing, but of course the whole point of action sequences is that they free our mind from needing to pay attention, so this is not a strategy I particularly recommend. However, if there are some action slips that you are particularly prone to, you might want to try this.

The most useful thing you can do is simply be aware of the circumstances that set you up for such errors. Then you can either:

  • make a sterling effort to pay attention when it's important to you (for example, both my partner and I are careful when we are driving and need to depart from familiar routes, to remind ourselves - or each other - of our destination at key points), or
  • use an object to signal that you have done something, or remind you where you are in a sequence (to take the recipe example again, you could move used ingredients to a particular part of the kitchen bench), or
  • decide it's not important!

This article originally appeared in the December 2003 newsletter.


  1. Harris, J.E. & Morris, P.E. (eds.) 1984. Everyday memory, actions and absent-mindedness. Academic Press.
  2. Reason, J.T. & Mysielska, K. 1982. Absent-minded? The psychology of mental lapses and everyday errors. Englewood Cliffs, NJ.: Prentice-Hall.

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External memory aids

What are external memory aids?

External memory aids include such strategies as:

  • taking notes
  • making shopping lists
  • entering appointments in a diary or on a calendar
  • writing a memo to yourself
  • writing on the back of your hand
  • taking photographs
  • using clocks, oven timers, alarms on watches, etc
  • putting objects in a conspicuous place
  • putting a knot in your handkerchief
  • asking someone to help you remember

Making lists

Making lists or writing reminder notes to yourself, is one of the most widespread external memory aids. It seems that list-making is primarily helpful as a way of organizing (encoding) information, rather than its more obvious role in retrieving. More often than not, people do not actually use the list or note to ‘remember’. The act of making it is sufficient to aid later recall.

However, there are situations where list-making appears appropriate but is not in fact the best strategy. For example, one study found that waitresses who went from table to table to take drink orders were much better at remembering the orders if they visualized the drinks in particular locations rather than when they wrote the orders down1. It is perhaps the time pressure in that kind of situation that makes an internal strategy more effective than an external one.

When to use mental strategies

  • when you can’t rely on external prompts (e.g., acting in a play)
  • when external prompts are difficult to prepare (e.g., because you lack writing materials) or hard to use (you have OOS in your writing hand)
  • when you didn’t expect to need to recall something, and have nothing prepared
  • when using external aids interferes with other behavior (understanding what’s going on; taking orders; etc)
  • when carrying external aids would be undesirable or inconvenient (e.g., when driving)
  • when the interval between learning and recall is very short (as when you need to remember a phone number only long enough to dial it)

When to use external memory aids

  • when a number of interfering activities occur between encoding and recall (e.g., having to remember to buy groceries after work)
  • when there is a long time between encoding and recall (e.g., needing to make a doctor’s appointment two months in the future)
  • when internal aids are not trusted to be sufficiently reliable (as when precise details need to be remembered; or strict timing — when to check a cake in the oven)
  • when information is difficult, and doesn’t cohere easily (e.g., remembering lectures)
  • when there is insufficient time to properly encode information
  • when memory load is to be avoided (as when you are attending to more than one activity)

How effective are external memory aids?

In general, external aids are regarded as easier to use, more accurate, and more dependable, than mental strategies. However, with the exception of note-taking, there has been little research into the effectiveness of external memory aids. The most that can be said is that, by and large, people believe they can be effective (with the emphasis, perhaps, on ‘can’).

One problem with external aids is that most of them are highly specific in their use. Their effective use also requires good habits. It’s no good remembering to make a note in your diary if you don’t remember to look in it.


  • Intons-Peterson, M.J. & Fourrier, J. 1986. External and internal memory aids: when and how often do we use them? Journal of Experimental Psychology: General, 115, 267-280.
  • Intons-Peterson, M.J. & Newsome, G.L. III. 1992. External memory aids: effects and effectiveness. In D. Herrmann, H. Weingartner, A. Searleman & C. McEvoy (eds.) Memory Improvement: Implications for Memory Theory. New York: Springer-Verlag.
  1. Bennett, H.L. 1983. Remembering drinks orders: The memory skills of cocktail waitresses. Human Learning, 2, 157-169.

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