The Average Human Has an Accurate Memory myth

Does the Average Person Have an Accurate Memory?

The average human has a limited short-term memory and a fairly inaccurate long-term memory. This is due to the way we process, encode, and recall memories. Other factors related to memory, attention, perception, and our brain all play into our memory problems.

Why Do Humans Have Memory Problems?

Our memory accuracy problems come from a few places:

1. Our attention: Our ability to consciously focus on more than one thing at a time is limited. We can split our attention by alternating focus between details, but this comes at a cost of decreased awareness. Attention affects what we perceive and how we process, encode, and recall memories.
2. Our Perception: We have millions of specialized sensory receptors in our bodies and they can sense millions of stimuli every moment. When we sense something with any of our senses our subconscious chooses whether to perceive it or not (store it in our “sensory memory”). We can store a lot in our sensory memory but information is held for just 1/5 – 1/2 of a second before it “decays”.^[8] Unless conscious attention is applied, the subconscious will decide what is perceived and what becomes a short-term memory, mainly based on what has been “useful” in the past.
3. Our limited short-term memory capacity: The average short-term working memory holds anywhere from around 5 – 7 items at a time, and only holds them for about 20 seconds each. Important items that connect with other ideas you have or that have attention focused on them are committed to long-term memory to be recalled. The others are forgotten.^[3][4][5]
4. Our brain re-wires itself when it encodes and recalls information: Every thought and every stimulus we have rewires our brain and every thought changes our perception of reality. When we encode memories we make connections. When we recall memories, we recall them from lots of different places. This can result in the brain inserting false details in old memories and then re-coding them that way.
5. The subconscious, selective attention, and evolutionary hardwiring. Our brain is conditioned to be efficient and our subconscious makes a number of choices based on this. Our selective attention can filter out important details to a given situation if they wouldn’t typically be useful to remember. Bias (conscious and subconscious) plays a big role in our memory problems.

A film that explores “how memory works“.

Human Memory Processing Versus Storage

Our brains have pretty amazing long-term memories. We absorb millions of stimuli every moment, and each perceived sensory memory can move from short-term storage to long-term via our 86 billion neurons. Each neuron makes about 1,000 – 10,000 connections creating a neural network with outstanding storage and processing power. This all runs on about 20 Watts of power (assuming body takes 100 Watts worth of calories and brain takes 20% of power).

The storage space is vast, but the filter we use to decide what goes in long-term memory is limited. As explained above, we can only process a few items at once, our attention spotlight only really focuses on one of those at a time, and a lot of the decision making is hardwired and done subconsciously.

Our memory problems usually come for our processing limitations, not storage or comprehension limitations.

How Does the Brain Process Memory?

The brain processes memories by directing attention (consciously or subconsciously) at stimuli and then uses the memory related parts of the brain to process that information.

First we receive input from stimuli via our senses. This is stored in sensory memory for only a few short moments. We then orient our attention (either purposefully or as a reflex) alternating focus between as many as 5 -7 pieces of information. These pieces can be retained in short-term working memory (AKA short-term memory or working memory) for up to about 20 – 30 seconds. We then decide which pieces are important and commit those to long-term memory (long-term memory = bits of sensory information stored in neurons and connected via synapses).

A video from Khan Academy looking at how the brain processes sensory, working, and long-term memory.

Memory Problems Related to the Different Types of Memory

There are a few different models, or theories, of how to describe the memory process. The Baddeley and Hitch model below is still widely used, so we will explain memory using this model.

Simple version of the working memory model: Sensory input -> sensory memory -> attention -> working memory -> long-term memory.[7]

You can learn more about the different memory types and the Baddeley and Hitch model here (there is tons of information, and that will help you understand why memory can be so wonky).

NOTE: This model explains memory and doesn’t talk about which parts of the brain are controlling which pieces. We have biological explanations, but they are complex, so we can talk about them separately.

Sensory Memory and Attention

We can take in a lot of sensory data but we can only focus our attention on a few at a time.

Our brain keeps these sensory memory blips for only a matter of seconds. Then we must decide (consciously or subconsciously) which of these blips to orient our attention to and store in short-term working memory (AKA short-term memory or just working memory).

NOTE: Attention also dictates which stimuli we take into our sensory memory. We can recall short-term memories from long-term memory.

Short-term Working Memory

The brain can store about 5 – 7 pieces of information in working short-term memory. This is the information a person can hold in their conscious mind and alternate their focus between.

In the 1 – 20 seconds the information from your senses is stored in working memory you must (either consciously or subconsciously) use your “brain power” decide which pieces of information are useful. Useful information is transferred to long-term memory, non-useful pieces of information are discarded.

Long-Term Memory

Long-term memory can last anywhere from a few hours to a lifetime. For all of our short-term memory and attention limitations, our long-term memory is very vast. The problem is, it isn’t always very accurate.

Our long-term memory isn’t like the files on your computer, which contain audio, video, and text programs. Rather, memory is just 86 billion neurons, which each receive and store a bit of sensory information. These neurons are connected through about 1,000 – 10,000 synaptic pathways each.

When two neurons fire at the same time a connection is strengthened. When we recall a memory, we are calling on a network of neurons to reform the picture. The stronger a connection, the easier the recall. It is in the recall process that things start getting messy and our memory begins getting untrustworthy.

Eyewitness Testimonies and Memory

A number of studies have shown that eyewitness testimonies are not as useful as one may expect. The problem is that our memories are actually very susceptible to suggestion. Perjury is defined as “knowingly making a false statement”, but the truth is our memories are so untrustworthy on average that the average person would have no way to tell whether they were making a false statement or not.^[1]

Original Memory Versus Recalled Memory

Original memory is your memory the way you experienced it. Because of your lack of attention, on average, the original memory isn’t an accurate recount of an event. It is a recount of your experience of the event with the potential that you have filled in the blanks. Everything you committed to long-term memory, including half-truths and lies is in the original memory.

Recalled memory is the version you get any time you “play back the tape”. The thing is, you don’t just encode and store a memory in one place; your brain makes a matrix of connections to different places. You remember the space of the room, the sounds, the smells, the visuals, the touch, etc. Your brain, on the fly, jigsaws together the puzzle pieces recreating a scene. Typically this is done at the request of an outside stimulus or inside thought as a trigger (your brain orients attention in a few different ways). Whether a smell reminds you of something, a direct question does, or your purposely try to recall the memory on your own accord your brain accesses a memory when prompted. Once your brain starts putting the pieces together, the trouble starts. Your brain is likely to fill in the blanks it doesn’t have when accessing memory, if something is suggested in any way the brain has a tendency to fill in memory gaps with the details (true or not).^[6]

Ways to Access Memories

There are two main ways to access (or “recall”) a memory, they are: recognition and recall. Humans are generally good at recognition; we can pick a face out of a crowd and commit many faces to memory with little work.

One the other hand, humans aren’t hardwired to be great at recall. The more important a detail the better we recall it. For example “fire burn, fire bad”. That is an easy connection to make. Remember what color hat your friend wore on Friday, as it’s not a useful or often recalled, is much harder to remember accurately (unless you focused your attention on it purposefully or connected that information in meaningful way). As long as our brain makes sense of the recall, it has done its job. This is fine for every day occurrences, but when exact details are needed our memories start to show their weakness.