So You Think Your Memory is Bad? Well, it’s actually worse than you thought.

Jul 9, 2010

Imagine yourself walking down a familiar street approaching a stranger who is obviously lost, staring hopelessly at a map.  As you saunter by you provide eye contact and a look of willingness to help. He asks you for directions.  As you begin to offer your advice, you are interrupted by a construction crew carrying a large door.  They walk right between you and the stranger.  Now imagine that as the construction crew parted you visually from the stranger a new and different person covertly took on the same lost role.  This new stranger is wearing different clothes, is taller by three inches, has a different build, and different vocal qualities.  Do you think you would notice?


Chabris and Simons (2010) in the The Invisible Gorilla share the results of a study carried out by Dan Simons and a colleague where they tested whether people would notice such changes in a scenario very much like the one I just described. When the scenario was described to undergraduates, 95% believed that they would certainly notice such a change (as is likely the case for you as well). Yet when this experiment was carried out in the real world, nearly 50% of the participants did not notice the switch!


This particularly startling data is indicative of change blindness, defined by Chabris and Simons (2010) as failure to notice changes between what was in view moments before and what is in view currently. Essentially, we tend not to compare and thus notice stimuli changes from moment to moment. As a result we tend to be “blind” in many cases to pretty obvious changes. And what is equally salient is that we are unaware of this blindness. If you are like most people you said “No way I’d miss that!” Yet it is likely that about half of you would miss such changes.


Unconvinced? So were a group of Harvard undergraduates who had just attended a lecture that covered the above “door study” and change blindness. After the lecture, students were recruited to participate in further research. Interested students were directed to a different floor where they were greeted by an experimenter behind a counter. As the recruits proceeded to review and complete the necessary paperwork, the experimenter who greeted and instructed them regarding the paperwork ducked down behind the counter, presumably to file some papers, only to depart as a new and different experimenter took over the role. Even after being primed with the knowledge of change blindness, not one of the students noticed the swap! This was true even for some of the students who had just moments before boldly stated that they would notice such a change. We are in fact largely blind to our change blindness regardless of our confidence regarding our vigilance.


These results, contend Chabris and Simons, comprise conclusive evidence for the illusion of memory, (which is the disconnect between how our memory works and how we think it works).


Most of us are all too aware of the failings of our short-term memory. We often forget where we put the car keys, cell phone, or sunglasses. These authors note that we are generally pretty accurate when it comes to knowing the limits of this type of memory. License plates and phone numbers have only seven digits because most of us can only hold that much data in short-term memory. However, when it comes to understanding the limits of our long-term memory we tend to hold entirely unrealistic, fallacious, and illusory expectations.

In a national survey of fifteen hundred people [Chabris and Simons] commissioned in 2009, we included several questions designed to probe how people think memory works. Nearly half (47%) of the respondents believed that ‘once you have experienced an event and formed a memory of it, that memory doesn’t change.’ An even greater percentage (63%) believed that ‘human memory works like a video camera, accurately recording the events we see and hear so that we can review and inspect them later.” (Chabris & Simons, 2010, pp. 45-46).

They added:

People who agreed with both statements apparently think that memories of all our experiences are stored permanently in our brains in an immutable form, even if we can’t access them. It is impossible to disprove this belief… but most experts on human memory find it implausible that the brain would devote energy and space to storing every detail of our lives…” (p. 46).

So, as it turns out, our memories of even significant life events are quite fallible. Although we perceive such memories as being vivid and clear, they are individual constructions based on what we already know, our previous experiences, and other cognitive and emotional associations that we ultimately pair with the event. “These associations help us discern what is important and to recall details about what we’ve seen. They provide ‘retrieval cues’ that make our memories more fluent. In most cases, such cues are helpful. But these associations can also lead us astray, precisely because they lead to an inflated sense of precision of memory.” (Chabris & Simons, 2010, p. 48). In other words, our memories are not exact recordings, they are instead modified and codified personal replicas that are anything but permanent.


I cannot do justice to the impressive and exhaustive detailing that Chabris and Simons provide in the The Invisible Gorilla regarding the illusion of memory. However, suffice it to say, that we give way too much credit to the accuracy of our own long-term memories and have unrealistic expectations regarding others’ recall. People recall what they expect to remember and memories are modified over time based on malleable belief systems. Memories fade and morph over time depending on the “motives and goals of the rememberer.” (Chabris & Simons, 2010, p. 51).

“Although we believe that our memories contain precise accounts of what we see and hear, in reality these records can be remarkably scanty. What we retrieve often is filled in based on gist, inference, and other influences; it is more like an improvised riff on a familiar melody than a digital recording of an original performance. We mistakenly believe that our memories are accurate and precise, and we cannot readily separate those aspects of our memory that accurately reflect what happened from those that were introduced later.” (Chabris & Simons, 2010, pp 62-63).

They detail with riveting stories continuity errors in movies, source memory errors (is it your memory or mine?), flashbulb memories, and false memories in a way that really drives home the point that our memories are not to be trusted as factual depictions of historical fact. They beg the question: Can you trust your memory?


The answer: Partially, but you must be aware that your memory is not immutable. It is erroneous to assume that your memories are factual and it is equally fallacious to presume that other’s memories are likewise infallible. Two people witnessing the same event from the same perspective are likely to recall the event differently because of their unique personal histories, capabilities, internal associations, and thus their unique internal cognitive associations, as they store into memory the bits and pieces of the event.


Isn’t it amazing and scary that we give so much credit and power to eye-witness testimony in the court of law? Such power is conferred based on the pervasive and deeply held belief in the accuracy of memory – which you must know by now is an illusion. This is just another example pertaining to the illusion of justice in this country.


On a more personal level, next time you and your significant other get into a debate about how some past event went down, you have to know that you both are probably wrong (and right) to some degree. There is your truth, their truth, and the real truth. These can be illustrated in a Venn Diagram with three circles that from time to time have various degrees of mutual overlap. We must admit that over time the real truth is likely to become a smaller piece of the story. This necessitates that we get comfortable with the reality that we don’t possess a DVR in our brains and that we part ways with yet another illusion of the importance and power of our uniquely human intuition.




Chabris, C. F., & Simons, D. J. (2010). The Invisible Gorilla. New York: Random House.


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