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The Psychology of Why We Forget Things

Updated on August 28, 2015
Thomas Swan profile image

Dr. Thomas Swan studied cognition and culture at Queen's University Belfast. His work explores theories of emotion, attention, and memory.

Forget-me-nots have become a symbol of remembrance.
Forget-me-nots have become a symbol of remembrance. | Source

The Evolution of Memory

If evolution could create perfect human beings, our memories would be capable of recalling every detail from our lives. Unfortunately, evolution is a steady, imperfect process in which living organisms adapt sequentially to immediate threats in their environment. Although a perfect memory would help us survive, the challenges we face haven't made it necessary. Squirrels, on the other hand, need to remember the location of vast quantities of nuts, and their memory has evolved to become greater than our own.

Despite this inevitable limit on human memory, evolution has at least determined the type of information that is most likely to be forgotten. Indeed, people who remember useful information are more likely to survive. Thus, the genetic traits that cause them to prioritize useful information pass to future generations. For example, humans have developed a tendency to forget things that happened to them a long time ago. This is because older information is less relevant to present concerns, making it a low priority. At the biochemical level, this can also occur through a process called neurogenesis.

Neurogenesis Makes Us Forget

Research published recently in Science found that neurogenesis, in which new neurons are created by the brain, can cause older memories to degrade or disappear. As neurogenesis occurs prolifically in younger brains and decreases as we get older, the researchers tested different ages of mice and other small mammals to see how long it would take them to forget that touching another cage would cause a small electric shock. They discovered that younger mice forgot substantially quicker than older mice. When they used drugs to slow neurogenesis in younger mice, their memories improved to the levels of older mice. The research could be applicable to humans as it would explain childhood amnesia (forgetting one's early childhood).

Although neurogenesis is likely to degrade long-term memory, and evolution is likely to have improved the retention of useful memories, this doesn't explain why we forget useful, short-term memories such as where we left our car keys a couple of hours ago. In fact, neurogenesis and evolution seem to argue against it. So, to address why we forget our car keys, we must draw on another piece of fascinating psychology research.

Short-Term Memory Loss

The cognitive psychologist, Gabriel Radvansky, performed a number of ground-breaking experiments to show why we forget information about objects we've recently interacted with.

In the first experiment, Radvansky created a virtual environment in which participants took an object from one room and deposited it in the next room. Once an object was picked up, it was no longer visible in the environment. Participants transferred a number of objects, and their memories were occasionally probed to see if they could remember the object they’d picked up in the previous room or the object they’d deposited in the present room. Radvansky found that we’re far less likely to remember objects we've put down. He concluded that dissociating oneself from an object causes the memory of it to become less accessible. Thus, just like when we can’t find our keys, the memory is there, but it's frustratingly difficult to access!

A virtual environment displayed geometric objects on a number of tables.
A virtual environment displayed geometric objects on a number of tables. | Source

For some of the participants in Radvansky’s second experiment, there was no need to enter a second room before depositing the object. Participants covered the same distance in the virtual environment, but there was one large room instead of two small rooms. As before, once a participant picked up an object, it was no longer visible to them. Radvansky found that when participants didn't have to pass through a doorway, their memory for the object being carried or deposited was better than when a doorway was present.

Thus, Radvansky confirmed that two cognitive effects are in play. Passing through a doorway or putting down an object makes us more likely to forget about it. The two effects do not combine as much as one would expect. For example, putting an object down and passing through a doorway makes our memory marginally worse than doing one or the other. A possible explanation is that both effects utilize some of the same processes for making a memory inaccessible.

The Psychology of Memory

Given that we discard objects and pass through doorways on a regular basis, it's surprising that our memories are noticeably affected by doing so. However, if we recall that human memory has evolved to prioritize information that is most relevant to our present circumstances; an explanation is possible.

For example, entering a new room is more likely to make information about objects and events in the previous room less relevant to one's present concerns. Relatively speaking, staying in a single room makes everything in that room more relevant. This doesn't mean our minds have evolved to detect doors, rather, doorways are recognized as an event boundary between one environment and the next. It appears that changes in scenery set in motion an automatic updating process, akin to neurogenesis. New information about the current environment starts being collected, while information about the previous environment is made less accessible.

The reason we sometimes forget useful information, such as where to find keys, is because our brains do not consciously calculate its relevance. Instead, our brains automatically determine what's relevant via cognitive cues. These are events that have come to consistently mark the point at which information becomes less relevant. As discarding an object or changing scenery are common precursors to an object losing relevance; these events cause related memories to become less accessible. These cognitive cues are shaped by what is most beneficial to us. For example, objects currently in one’s possession could prove useful for future tasks (or to counter threats) whereas discarded objects are relatively useless in these potential scenarios. In other words, when faced with a crisis, it's better to remember what you have on you than what you don't!

Early humans (red) had to adapt to new environments occupied by Neanderthals (beige) and Early Hominids (green). Numbers show years before the present.
Early humans (red) had to adapt to new environments occupied by Neanderthals (beige) and Early Hominids (green). Numbers show years before the present. | Source

Nature or Nurture?

These two cognitive effects on short-term memory may be the result of developmental learning, i.e. training our minds to recognize relevant aspects of our environment. However, there are a couple of reasons to think this isn't the case. First, these memory constraints are unconscious and automatic, meaning they're impossible to completely overcome. No matter how many times we forget the location of our keys, we keep losing them! Second, children display these effects more than adults, although further tests are needed to confirm this trend.

It appears likely that these two cognitive effects are as unavoidable and innate as neurogenesis. Indeed, the course of our evolution is characterized by our ability to adapt to new environments. When humankind left Africa to populate the world (see above), we were venturing into unknown lands with treacherous conditions, new predators, and new tools at our disposal. It would have been beneficial to forget irrelevant information about older environments.

Individuals who were adept at this propitious pattern of forgetfulness would have adapted better to the new way of life. Their survival may have left a lasting footprint on the brains of their descendants, and the effects revealed by Radvansky in his experiments appear to demonstrate this legacy.

Other Reasons For Forgetfulness


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    • Thomas Swan profile imageAUTHOR

      Thomas Swan 

      7 years ago from New Zealand

      Thanks for commenting d.william. Yes, I think having a one-track mind would relegate other memories to the back of your mind... simply because they're not being used or thought about.

      I have left the stove on occasionally too. It's usually at the end of cooking rather than the start. After a few times I got a bit OCD about it, and now I repeatedly check to make sure it's off before leaving the room. It's a good example because, in this case, leaving the room is exactly what causes us to forget. It's worth making a point to turn everything off, including light switches, before leaving a room.

      You know, only a few days ago I left my back door open from 9pm to 3am! Very dangerous, but it was because I opened it in preparation for putting a wasp outside. I can't stand wasps! It took a while to get it to leave the house, but it went out a window instead, so I left the door open until I went into the kitchen again. No matter how hard we try to avoid them, these memory traits are imprinted on our minds.

      The timer sounds like a really good memory aid because it links two events. I'd probably be too lazy for that though!

    • d.william profile image


      7 years ago from Somewhere in the south

      Thank goodness i ran across this article. I was beginning to think i was starting to become senile (L.O.L.). I constantly lose my car keys, and other objects.

      My mind is so filled with searching for new things to write about i tend to forget where i put things down.

      So, i guess my problem is not 'forgetting' per se, but rather having a 'one track mind'. I still have not learned to not put anything on the stove to cook before i come to sit down at this computer to write, or read, articles. I forget the stove and what is cooking until i smell it burning.

      The only way i have found to offset this 'one track mind' thing is to set a timer and put it near the computer. When it goes off, i jolt back to the present, and realize i had totally forgotten about what is on the stove - again.

      I used to be great at multitasking with mundane chores, but when trying to find the best way to say something in writing those mundane chores totally lose their relevance.

    • Thomas Swan profile imageAUTHOR

      Thomas Swan 

      7 years ago from New Zealand

      Thanks for the comment noorin. It's an interesting suggestion that a spartan exam environment could disorient those who rely on spatial memory cues. It could mean that the environment is not such a fair playing field after alll.

    • noorin profile image


      7 years ago from Canada

      Interesting article Thomas.

      I find the "Brain" and memory in particular to be one of the most fascinating topics in psychology. The experiment kinda explains a lot about my chaotic relationship with keys :P

      And the "Cue Dependent Forgetting" theory mentioned in the clip totally explains why I tend to forget info in exams or more precisely why that info sets on the tip of my tongue and refuses to go any further sometimes. I guess when I study, I rely on lots of cues, but once those cues are taken away from an exam setting, the info tends to fade away.

    • Thomas Swan profile imageAUTHOR

      Thomas Swan 

      7 years ago from New Zealand

      Thanks Elias, psychology and neuroscience is certainly where the most exciting research is being done right now.

    • Elias Zanetti profile image

      Elias Zanetti 

      7 years ago from Athens, Greece

      A very interesting, well research and well written hub, Thomas. Brain and its functions is such a fascinating subject and modern science has just recently started to demystify its various processes.

    • Thomas Swan profile imageAUTHOR

      Thomas Swan 

      7 years ago from New Zealand

      Thanks for the comments jabel and pstraubie. The doorway conclusion seems more plausible if you think about doors as representative of something more general. If our minds consider doors as representing an `event boundary' between two environments, it's plausible that they would cause memory of the previous environment to lessen. One thing they should have tested is whether memory of the new environment was better after passing through a door. I think that would have confirmed the effect. The experimental group had 36, and the control group 15, but the difference between the two was significant. In the hub, I've linked to Radvansky's paper (on the word "experiment"). I think he's done a follow up experiment too, which appeared confirmatory.

    • pstraubie48 profile image

      Patricia Scott 

      7 years ago from North Central Florida

      This was very interesting. I just wonder about the passing through the doorway conclusion. How large was the control group that participated in the study that came up with that conclusion?

      I do not doubt it as I forget things without passing through a doorway!!

      Thanks for sharing ps

    • jabelufiroz profile image


      7 years ago from India

      Impressive hub on THOMAS SWAN. Voted up.


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