Power and Limits of Our Memory

Memory seems so simple a topic

How powerful is human memory? What are its limitations? How much attention do we have to be paying to remember something?

We have many kinds of memory like when we recall things from awhile ago, like facts (semantic memory), how to ride a bike (procedural memory) and personal experiences (episodic memory). When we need to keep things in mind, like a list of groceries while we walk about, we're using short-term memory (STM). We're not going to remember our list years later. We don't need to. It's just what we're keeping in mind at a moment. During the activity, you completed a classic STM measure called a forward digit span task. It's "forward" because you recalled exactly what you were told. You didn't do anything with your memory other than hold it. if I had you do something, like repeat the numbers backwards in a reverse digit span task, you would be combining STM with processing and we call it working memory. Let's focus on short term memory.

Just how much can we keep in mind even if we're doing nothing beyond holding it in mind? Notice figure 1 shows us how many people could remember digits perfectly for different lengths of sequences. Pretty much everybody can recall 2, 3, or 4 digits, but then it gets harder. A small percent of people can hold 8 or 9 digits in mind, but pretty much nobody can remember more. Generally, most people can hold about 5 to 9 chunks of information in their mind at a time. Many early psychology researchers looked at short term memory tasks, and in a classic review George Miller realized across lots of tasks like our forward digit span, people have a capacity of 7 ± 2 chunks.

Based on the largest sequence you remembered perfectly and how much of other sequences, I estimated how many chunks you can hold (figure 2). In case you worry you have a smaller capacity, please know you have many other ways to remember, like putting notes on your phone so you don't need to keep everything in mind. We can learn things more deeply so each chunk is actually much more than one item. You might notice with our activity the average is about 6 instead of 7. That's probably because you didn't do the activity in a distraction-free lab so some of your capacity was lost to other things. Short-term memory has its limits.

Despite short term memory having limits, a strikingly powerful kind of memory we have is implicit memory. Learning things usually requires attention, there is an exception. Implicit learning occurs when we learn patterns without our conscious awareness, such as probabilities or frequencies. Typically we are unable to verbally explain our implicit knowledge, but we show we know it in behavior our behaviors and choices. Among the most famous examples is how we just absorb our native language; we can follow complex grammar rules even though most of us can't explain how we do it (e.g., Reber, 1967).

Implicit memory is surprisingly different from explicit memory. There's very little variability in implicit learning ability. Age does not matter to implicit learning ability. Disorders that harm memory rarely impact implicit learning. IQ is not related to implicit learning. But implicit learning does not transfer to new tasks, even ones so structurally similar.

As a concrete real-life example, I'm a avid roller skater. I can cross my legs over each other, skate on one leg, skate backwards, twirl and so forth. But if you ask me how I do it, it's hard to explain. Skating is implicit procedural knowledge. I like to ice skate too. It's practically identical. Movements are often the same, like swizzles. But the feel of blades on ice is different than wheels on wood. I kept falling when I started. It's hard transferring my abilities, so I had to learn again. Then, after I learned to twirl on ice, I had to relearn twirling on roller skates (because it's way harder on wheels)! And non of this learning is conscious. It's a feel. So did you implicitly learn anything during our memory activity?

You had no idea I'd ask you how fast the digits went by. So you might think your guesses were random. But they're not! Overwhelming you said it was like B, which really is the same speed, χ²(2)=291.21, p<.0005, N=673!

You didn't know I'd ask, but you clearly identified the least common digit (4) as least and your rarest choice for least was 5, the most common digit. When I asked you the most common digit, you mostly chose the correct answer 5. The digit 6 was a popular choice too, and this isn't random. Six (6) was the most common digit in the first position of sequences. It's easiest to remember the first things we learn, which is called the primacy effect.

You had no idea I'd ask you about the typography of the numbers. But you didn't guess randomly (figure 4). H is the correct answer which is among the most popular. It looks a lot like A and B. My guess is many of you chose A or B because you're more used to seeing them. Let's come back to this point because it's kind of a false memory of yours.

Is our memory a perfect recording of reality? No, many things tweak our memory. And these tweaks are not random. We can predict false memories. Notice our implicit memory task about typography (figure 5). I purposely chose a rarer font for the digits but purposely chose one a lot like the most commonly used ones. When you got it wrong, you most often chose fonts you know. Your prior knowledge of fonts interfered - colored - your memory of the task you were doing. This is prospective interference because the knowledge you have came first.

Scarily, we can even "implant" false memories in people! Even after the fact! Are you immune?

Through the entire set of forward digit span tasks you watched numerals go by with a yellow rectangle around them the entire (figure 6 upper right) time. Later I asked you what color that border was. How simple! You had so much exposure to the yellow box, and you were focused on it. How could you get it wrong?

Yellow was a frequent choice (figure 6, left), not the MOST frequent chioice. Black was probably a guess when color just didn't stand out to you and you're used to frames in black on websites. You experienced another prospective interference. But why did so many answer blue? The directions for the implicit activities items said things like:

After the fact - retroactively - I implied something false about the reality you literally just experienced. It interfered with your memory, called retroactive interference. These kind of false memories happen all the time. For example, after watching a movie together, the people were instructed to make jokes about the movies main character by making up scenes. Several weeks later they cam back to the lab separately and were asked to recall everything they could of the movie. Almost half of the participants included a made-up scene as a real scene (Chrobak & Zaragoza, 2008)! And infamous example comes from the 1980's when horrific reports of abuse by day care providers spread rampant. Police understandably wanted to catch the bad guys so when children they interviewed didn't reveal abuse, police asking leading questions. What they didn't realize is they were unwittingly implants false memories in children. Fortunately, Elizabeth Loftus (1998) studied the phenomena extensively and today police are trained how to question children, and adults, so they don't accidentally interfere with memory.

The false memory 'implanted' in you is about color. I chose it to be as innocuous as possible. But since it's color, the task might not work if you have color blindness, especially if you have Tritanopia (blue-yellow color blindness). I needed a filler task before the implicit memory tasks so I gave you several items assessing your color vision. Your certificate might caution you how you may have color blindness, please know the task is not a diagnosis. It's especially likely inaccurate if you used a small screen (e.g., phone) or dimmed your screen brightness. If you're concerned about your color vision, I recommend completing an online activities specifically meant to measure color vision: Farnsworth Munsell 100 Hue Test and the Ishihara Test. Please use a bright larger screen. Save your results if they raise a concern for you and bring them with you to a optometrist or ophthalmologist for a proper diagnosis. There is help available if you have color blindness such a special contacts and glasses.

Our memory can be incredibly powerful! Our implicit memory is striking - we can remember things we didn't event know we were aware of. But memory has it's limitations too. We can only hold so much in mind at a time. But fortunately people are creative and we have ways to remember, like creating notes for ourselves. Many cognitive processes help us gather and use information, but they never create a perfect record. And among the things we need to be aware of is how much interference can mixed up our memories.

Uneasy Feelings about Your Results?
Please remember your results with any activity are not who you are. Your results are a 'snapshot' of a moment when you did an activity. It's just one measure, a single thread, of the many strands of who you are. Any result is a guess with statistical error. And it's possible the measure is flawed in a way so it doesn't work for you. Please do not think of your results as definitive dogma. Instead they're a starting point for our self reflection. Please keep in mind too, self-reflection can feel uncomfortable. "Bad" feelings are not actually bad. They're information. So, even if your activity result is inaccurate and flawed, you might ask yourself what your feeling is trying to tell you? Trusted teachers, friends, and therapists can be helpful. I wrote an essay elaborating with concrete examples how we can appreciate uneasy feelings about our activity results.

Scholarly Information?
You're welcome to use Copernican Revolution activities and essays for your thesis and studies. Having information about scholarly aspects like psychometric data, activity design details, and norm calculations may help. The primary focus of my essays is connecting educated laypersons with psychology. To help people like you, with advanced academic interests, I add an appendix with each activity.

Chrobak, Q. M., & Zaragoza, M. S. (2008). Inventing stories: Forcing witnesses to fabricate entire fictitious events leads to freely reported false memories. Psychonomic Bulletin & Review, 15(6), 1190-1195.

Loftus, E. F. (1998). The price of bad memories. Legal and Criminological Psychology, 3(1), 87-94.

Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63(2), 81-97.

Reber, A. S. (1967). Implicit learning of artificial grammars. Journal of Verbal Learning and Verbal Behavior, 6(6), 855-863.