Sometimes, it seems that for every occasion when we are able to remember something, there is another frustrating occasion when memory lets us down. Why does this happen?
We frequently forget things, but it can seem baffling why this should happen in some instances and not others. Psychologists have found that forgetting is the result of a number of factors that can affect any stage of the memory process.
Sometimes, forgetting happens because we fail to register a piece of information in the first place. For example, if someone speaks to you while you are reading this page, you might not really take notice of what is being said, and so never form a memory of it. In some ways, this is the most fundamental form of forgetting – if memory is never stored d, then it cannot be remembered later, no matter how hard you try. After you have taken in a new piece of information, the delay before you come to recall it can be as short as half a second or as long as 50 years, and loss of the information can occur at any stage. However, the exact way in which we forget stored information is controversial. Some researchers think that memories simply decay, while others believe that it takes other memories to disrupt them.
Decay or interference?
The idea that memories decay – in other words, that they fade away over time – was put forward by Hermann Ebbinghaus, a pioneering 19th century German psychologist. Ebbinghaus made himself the subject of his own memory experiments using lists of made-up words, which he learned and then tested himself on after varying periods of time. He found that soon after reading the lists, there was a period of rapid forgetting, and much of what he had learned was lost. Then, as time went on, more for getting took place, but at a slower rate.
Ebbinghaus came to the conclusion that his memories were fading away over time. It is true that the longer we hold something in memory without actively refreshing its trace in the brain by recalling it, the more likely we are to forget it. However, psychologists cannot tell for certain whether this is simply because memories fade or because other factors also contribute.
Retroactive and proactive interference
Memories can take up to three years to become lodged permanently in the brain, and we do not switch off our minds to other materials while we are storing them. We are continually experiencing impressions and thoughts that create new memories that can interfere with existing ones. This is particularly true if we are learning something that is similar to the original material. For example, if you are trying to remember a person’s name, you will find it even more difficult if you are told the names of other people in the meantime. This type of interference – in which new information interferes with old – is known as retroactive interference. However, old memories can interfere with new ones in the form of forgetting, known as proactive interference. This type of interference applies to many everyday experiences. For example, previous phone numbers, addresses, car number plates, and even the name of a pet from long ago can pop up and interfere with the recall of more recent information. Some researchers argue that all forgetting may be largely due to some form of interference rather than memory decay.
Problems with retrieval
Forgetting occurs most frequently when we are trying to recall something quite specific information. A typical situation is when you are fairly sure that a piece of information is stored in your memory, but for some reason, you can not quite retrieve it. Often, this is only temporary, and the relevant snippet seems to surface of its own accord minutes, hours, or perhaps days later. The experience might be better described as ‘ failing to remember rather than forgetting. The fact that memories can be mislaid in this way and then found again later shows that there is a vast amount more stored in the memory than we can access at any one moment.
Problems with recall occur because memories are inter linked. We access them by following the links from one to the next until we find what we need, but sometimes these links are temporarily blocked, and we are left with a ‘tip-of-the-tongue’ effect – the certainty that we know something, but it is just beyond reach. At other times, the detail we need is held in check by what psychologists call an ‘ ugly sister’ – a similar word that seems bigger, stronger, and more immediate and so gets in the way of the right one. Every time the wrong word is activated, its neural trace is reinforced in memory, and some theorists suggest that nearby competing items are dampened down – among them, the actual word that we want.
The problems of prospective memory
There are some situations where people are particularly prone to forget ting. For instance, have you ever remembered, over breakfast, that you need to buy and send a birthday card when you go into town, then not thought of it again until the evening, when it is too late? This is an example of prospective memory – a term psychologists use for situations in which you must ‘ remember to remember. Having remembered the birth day in the first place, you had to remember to do what you planned to do about it (buy a card) later in the day when you were near a shop. This need for ‘ double remembering ‘ makes prospective memory the most difficult form of memory there is. That is why diaries and organizers are so essential for most of us. They not only make it easier to remember things like addresses and telephone numbers, but they also reduce the strain on prospective memory – provided, of course, that you remember to look at them regularly.
When we need to forget
For every occasion when we need to remember, there are as many situations where it is helpful to forget. A traumatic event, for example, can leave an indelible imprint on memory and may resurface unprompted for many years afterward. On a lesser scale, we sometimes become fettered to past mistakes and embarrassments and feel the full force of our original emotions each time we recall them. Any useful lessons from such events will probably have been learned long ago, making rehearsal of them pointless. We should review them candy in better times, divest them of their emotional heat, and then leave them in memory – unrecalled and regarded.
Forgetting is essential in some occupations where people have to learn large amounts of information rapidly and then use it for only a short period of time. Courtroom lawyers, for example, need to relinquish their grasp of the details of the previous brief each time they take on a new case, and actors in four-episode-a-week soap operas have to learn and then forget scripts at an even faster pace. The repetitiveness of our daily experiences also makes forgetting inevitable and essential. If we make the same journey to work every day, it is pointless to remember each one in perfect detail. For this reason, your memory retains only the occasions that were more notable. For example, a month of bus rides may pass in a blur, but the day you were soaked in a downpour and then thrown off the bus because there was ‘one too many on board. I’ll stick it in your memory. The disadvantage of this type of forgetting is that even enjoyable events such as Christmas holidays and parties tend to become indistin punishable over time.
Memory Under Stress
Our own experiences tell us that we are most prone to forgetting when we are anxious or under stress. Getting ready for a once-a-year holiday, for example, can be extremely stressful because it often involves timetables, erratic postal services, and copious lists of things to do and take – all of which make heavy demands on memory. It is unsurprising that each day, people turn up at airports without a passport, tickets, or a vital piece of luggage.
Studies of the effects of stress on memory point to the action of cortisol, one of a group of hormones called glucocorticoids that flood the brain when we are under stress. Cortisol reduces energy supplies to the brain and appears to interfere with its ability to store information in memory. In one experiment, researchers who gave students high doses of cortisol four days before a test found it significantly reduced their ability to memorize a written passage. After a week without cortisol, the students’ memory performance returned to normal – so a two-week holiday should be enough to rectify any memory damage caused by the stress of getting there!
