Mirror, Mirror: Memory As a Reflection of the Environment

Take a few minutes to reflect on these questions:

• Why is there a distinction between short-term memory and long-term memory?
• Why does forgetting happen?
• What are the environmental demands my memory?
• Why does a lot of forgetting happen initially, but then it tapers off?
• What is the optimal amount of time that I need to spend studying to remember something?

Why do we forget?

In a previous post, we graphed the forgetting curve of Hermann Ebbinghaus's study of his own memory. For very short delays, his memory was very good. But as the delays got longer, his memory for his list of trigrams (e.g., "LEK") dropped precipitously. Then the accuracy for remembering the list leveled off at around 20%.

We also drew a forgetting curve for the recall of Spanish vocabulary words across an entire life span. The shape of the graph was surprisingly similar to the forgetting curve of non-sense words used in Ebbinghaus's study. There was a large amount of forgetting initially, but then the percent of recalled words off at around 60%.

These two graphs are interesting in their own right, but you might be asking yourself the following questions: Why are these graphs shaped this way? Why are forgetting curves steep at first and then asymptote at some value? There must be a reason why memory works this way. Let's look to finches, moths, and ants for some answers.

Finches, moths, and ants...oh my!

During his trip to the Galápagos Islands, Charles Darwin noticed something peculiar about a particular family of birds. Although they were of the same family, there were several different species of finches, each with a distinctive beak. Some of the birds had a wide, stout beak; whereas, other finches had a sharp, pointed beak. It turned out that the different shapes aided the birds in consuming food for their different diets. The wide-beaked finches ate nuts and berries, while the sharp-beaked finches ate insects. In effect, the shape of the beak was optimized to the finch's environment, which included their dietary requirements [1].

But what happens if the environment changes? Can an organism's features evolve to respond to the change? It's hard to conduct a controlled laboratory experiment to answer this question; fortunately, a natural experiment occurred at the turn of the century. During the rise of the Industrial Revolution in Great Britain, the amount of pollution escalated rapidly. Ash from the factories coated trees in the surrounding region. Trees that once had light-colored bark, now covered in soot, turned to a dark gray. Resting on the bark of these trees was a species of moth, called the peppered moth. The most prevalent pepper moth had bodies that matched the original color of the tree bark. When the trees became gray, birds could now easily spot the white moths against the gray background. Due to some natural variation in pigmentation, some moths were born a darker color, which was much more difficult for predators to see. As the lighter colored moths were eaten, the ratio of darker moths to lighter moths tipped in favor of the dark-bodied pepper moths [2].

The study of finches demonstrated that species are optimized to their environment, and the study of pepper moths showed that the range of variation within a species can tilt depending on the factors that lend themselves better to survival. So far, however, this conversation has been about the outward appearance of an organism. What about an animal's behavior? Herbert A. Simon wrote this about the complex behavior of the ant:

Imagine watching an ant on the beach. Its path looks complicated. It zigs and zags to avoid rocks and twigs. Very reminiscent of complex behavior — what an intelligent ant! 

Except an ant is just a simple machine. It wants to return to its nest, so it starts moving in a straight line. When it encounters an object, it zigs to avoid it. Repeat until the destination is reached. 

Trying to simulate the path itself would be difficult, but simulating the ant is easy. It’s maybe a half-dozen rules.

The point of this parable is to illustrate the interaction between the environment and perceived complexity. Lots of complex looking things are really the result of the territory, the shape of the beach, and not the agent, in this case, an ant. 

But, of course, with this metaphor, I’m not really talking about ants. I’m talking about people. How much of the complexity of human behavior is really the product of the environment? [3]

Memory, as we have seen, is highly complex. There appears to be at least two different storage mechanisms (i.e., short- vs. long-term memory) and several different classifications of memory types (i.e., semantic vs. episodic; procedural vs. declarative). Can we explain the complexity of memory by looking at the environment? 

"All the news that's fit to print" (in memory).

To answer that question, we need a model of the environment, and see if it matches (more or less) to the models of memory that we currently have (i.e., the forgetting curves). How would you construct a model of the information in your everyday environment? That seems like a tall order. Since we live in an information-rich environment, it might be a good idea to narrow it down. 

That's precisely what two cognitive scientists did when attempting to construct their own model of the informational environment [4]. They decided to look at all of the words that appeared in the headlines of the New York Times for a two-year period (i.e., 730 days between Jan. 1, 1986 and Dec. 31, 1987). They tracked two variables. The first was the day on which a word appeared. For example, the word Challenger occurred on days 29, 31, 34, 36, 40, 44, and 99. Then they counted how many times that word appeared in a 100-day window (n = 7 for Challenger). These two variables allowed them to construct a retention function, which is the probability that a word will appear on the 101st day given n number of days since its last occurrence. 

To make that a little more clear, let's look at some hypothetical data (see Fig. 1). Suppose we want to know, What is the probability that a word will appear on the 101st day, given it has been 20 days since the last time I saw it? According to the hypothetical retention function, I have about an 11% chance of that particular word appearing. If it's been 100 days since the last I saw it, however, then the probability drops to around 3%. In other words, it is highly unlikely that a particular word will appear in my environment as more time passes since the last time it appeared. I think this makes intuitive sense. It's unlikely that we will read about Muammar Gaddafi today, given we haven't heard anything about him in several years.

Figure 1: A hypothetical retention function for words appearing on the 101st day.

To bring this full circle, it seems that our memory is like a finch's beak, a pepper moth's coloration, or an ant's path on the beach. Memory is optimized to the environment in which it operates; thus, memory is a reflection of the environment. The forgetting curves show that memory is solid for short durations, similar to the New York Times headlines model showing that it is highly likely that a particular word will show up again given a short delay [5]. But then as time goes on, that word is less likely to show up. So why bother remembering a piece of information if it is unlikely to appear again in one's informational world?

The STEM Connection

If memory is in fact a reflection of our environment, then what does that mean for the way we structure the informational environment in our classrooms? First of all, the forgetting curves reinforce the adage: Use it or lose it. If the informational environment does not demand that I remember something, then guess what? I'm probably not going to remember it. 

However, we can systematically and intentionally structure the information environment so that important declarative chunks or procedural memories are needed and exercised in a periodic fashion. If something is important enough to remember (e.g., the slope-intercept form of a linear equation), then keep bringing it up. Keep using important information. As the demands in the informational environment escalate, then students will rise to the occasion. If learned well, then it might even make it into the part of the curve that never goes to zero (i.e., permastore).


Share and Enjoy!

Dr. Bob

For More Information

[1] Darwin's finches

[2] Peppered moth evolution

[3] Simon, H. A. (1996). The sciences of the artificial (Vol. 136). MIT press.

[4] Anderson, J. R., & Schooler, L. J. (1991). Reflections of the environment in memory. Psychological Science, 2(6), 396-408.

[5] Some might argue that editors of newspapers and magazine's are sensitive to our ability to remember and therefore might decide not to write about something that occurred long ago. While that might be the case, Anderson and Schooler (1991) also used two other databases to construct their argument. They included a database of children's speech (CHILDES) and the second author's email inbox.