Thursday, January 27

Not remembering some things can be synonymous with a good memory


When asked the other day about a bakery near my house, I replied that I had recently eaten their delicious chocolate chip cookies. My wife corrected me, pointing out that the cookies I ate were actually oatmeal raisins.

Why did I make this memory error? Is it an early sign of impending dementia? Should I call my doctor?

Or is it good to forget the details of cookies, given that everyday life is filled with an abundance of details, too many for a finite human brain to accurately remember?

I am a cognitive scientist and have been studying human perception and cognition for over 30 years.

My colleagues and I have been developing new theoretical and experimental ways of exploring these kinds of errors.

Are these memory mistakes a bad thing, the result of faulty mental processing? Or, although it seems contrary to common sense, could those mistakes be a good thing, a desirable side effect of a cognitive system with limited capacity which works efficiently?

We lean towards the latter: that memory errors may actually indicate a way in which the human cognitive system is “optimal” or “rational.”

Are people rational?

For decades, scientists have debated whether human cognition is strictly rational.

Starting in the 1960s, psychologists Daniel Kahneman and Amos Tversky conducted pioneering research on this topic. They concluded that people often use quick mental strategies also known as heuristics.

For example, when asked if the English language has more words that begin with the letter “k” or have “k” as the third letter, most people say that there are more words that begin with “k.”

Illustration showing a brain and computing data
Memory errors can indicate a way in which the human cognitive system is “optimal” or “rational.” (Photo: GETTY IMAGES)

Kahneman and Tversky argued that people come to this conclusion by quickly thinking of words that begin with “k” and those with “k” in the third position, realizing that they can think of more words with that initial “k”.

Both scientists referred to this strategy as the “availability heuristic”: what comes to mind most easily influences the conclusion.

Although heuristics tend to work well, this is not always the case. Therefore, Kahneman and Tversky argued that human cognition is suboptimal. In fact, the English language has many more words with “k” in the third position than there are words that start with “k”.

Sub-optimal or the best it can be?

However, in the 1980s, new research began to appear in the scientific literature suggesting that human perception and cognition could often be optimal.

For example, several studies found that people combine information from multiple senses, such as vision and hearing, or vision and touch, in a statistically optimal way, despite noise in sensory signals.

Perhaps most importantly, the research showed that, at least some cases of apparently suboptimal behavior, are actually the opposite.

A baseball player throwing a ball
How well can you measure the speed of a ball coming towards you? (Photo: GETTY IMAGES)

For example, it was well known that people sometimes underestimate the speed of a moving object. So the scientists hypothesized that the perception of human visual movement is suboptimal.

But more recent research showed that the statistically optimal sensory interpretation or perception is one that combines visual information about an object’s speed with the general knowledge that most objects in the world tend to be stationary or move slowly.

Furthermore, this optimal interpretation underestimates the speed of an object when the visual information is noisy or of poor quality.

Because the theoretically optimal interpretation and the actual interpretation of people have errors in similar circumstances, it is possible that these errors are unavoidable when the visual information is imperfect. In other words, people actually perceive speeds of movement as well as they can be perceived.

The scientists found similar results when studying human cognition. People often make mistakes when remembering, reasoning, deciding, planning, or acting, especially in situations where information is ambiguous or uncertain.

As in the perception example of estimating visual speed, the statistically optimal strategy when performing cognitive tasks is to combine information from data, such as things one has observed or experienced, with general knowledge about how the world normally works.

Young man trying to remember something
People have a limited memory capacity: they cannot remember everything in detail. (Photo: GETTY IMAGES)

The researchers found that the mistakes made by the optimal strategies (unavoidable mistakes due to ambiguity and uncertainty) resemble the mistakes that people actually make, suggesting that people may be performing cognitive tasks as well as they can be performed.

Evidence has accumulated that errors are inevitable in perceiving and reasoning with uncertain information. If so, mistakes are not necessarily indicators of faulty mental processing. In fact, people’s perceptual and cognitive systems may be working quite well.

Your brain, under limitations

There are often limitations in human mental behavior. Some are internal: people have a limited capacity to pay attention; you cannot attend to everything simultaneously. AND people have limited memory capacity: cannot remember everything in detail.

Other limitations are external, such as the need to decide and act quickly. Given these limitations, people may not always be able to perform optimal cognition.

But, and this is the key point, although your perception and cognition might not be as good as they would be without restrictions, yes could be as good as possible under those limitations.

Consider a problem whose solution requires you to think about many factors simultaneously. If, due to attention span limits, you cannot think of all the factors at once, you will not be able to think of the optimal solution.

But if you think of as many factors as you can have in your mind at the same time, and if these are the most relevant factors about the problem, then you can think of a solution that is the best possible, given that your attention is limited.

The limits of memory

This approach, which emphasizes “limited optimization”, is sometimes referred to as the “resource-wise” approach. My colleagues and I have developed a resource rational approach to human memory. We think of memory as a type of communication channel.

When you put an item into memory, it is as if you are sending a message to your future self. However, this channel has a limited capacity and therefore cannot transmit all the details of a message.

Consequently, a message retrieved from memory at a later time may not be the same as the original message stored in memory. And this explains why errors occur.

If your memory store cannot faithfully hold all the details due to its limited capacity, then you will need to make sure that all the data it can hold is the really important data. That is to say, memory would be the best possible in limited circumstances.

Folders with documents in a filing cabinet drawer
Like a filing cabinet drawer, a human brain has a limit on how much it can store. (Photo: GETTY IMAGES)

In fact, scientists have found that people tend to remember details relevant to a specific task and forget details irrelevant to that task.

What’s more, people tend to remember the essence of a memory stored in memory, even if they forget the small details. When this occurs, people tend to mentally “fill in” the missing details with the most frequent or common properties.

In a sense, using common properties when details are missing is a kind of heuristic – it’s a quick and practical strategy that often works well but sometimes fails.

Why did I remember having chocolate chip cookies when, in fact, I had eaten oatmeal raisin cookies?

Because I remembered the essence of my experience, eating cookies, but forgot the fine details and therefore I filled in these details with the most common properties, namely chocolate chip cookies.

In other words, this error shows that my memory is working its best under its limitations. And that’s a good thing.

* This article was originally published on The Conversation. You can read the original version here.

Robert Jacobs is professor of brain and cognitive sciences at the University of Rochester, in the state of New York, in the United States.

It may interest you:

* 10 Early Alzheimer’s Symptoms You Shouldn’t Ignore
* Do you sleep less than 6 hours at night? Be careful because you could suffer from dementia
* An accident caused him to lose all his memories; what her boyfriend did to win her back is wonderful


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