When I was asked the other day about a bakery near my home, I replied that I had recently eaten its mouth-watering chocolate cakes. My wife corrected me and noticed that the cookies I ate were actually oatmeal raisins.
Why did I make this memory error? Is this an early sign of impending dementia? Should I call my doctor?
Or is it a good thing to forget the details of a dessert, given that everyday life is filled with an enormous number of details, too many for a limited human brain to remember exactly?
I am a cognitive scientist and have been studying human perception and cognition for more than 30 years. My colleagues and I have developed new theoretical and experimental ways of exploring this kind of error. Are these memory errors a bad thing as a result of incorrect mental treatment? Or, counterintuitively, could they be a good thing, a desirable side effect of a cognitive system with limited capacity that works effectively? We lean to the last – that memory errors can actually indicate a way in which the human cognitive system is “optimal” or “rational”.
Are people rational?
For decades, cognitive scientists have been thinking about whether human cognition is strictly rational. From the 1960s, psychologists Daniel Kahneman and Amos Tversky conducted groundbreaking research on this topic. They concluded that people often use “fast and dirty” mental strategies, also known as heuristics.
For example, when asked if the English language has multiple words starting with the letter “k” or with “k” as the third letter, most say that there are multiple words beginning with “k”. Kahneman and Tversky argued that people reach this conclusion by quickly thinking of words starting with “k” and with “k” in the third position, noting that they can think of more words with the initial “k”. Kahneman and Tversky referred to this strategy as the “accessibility heuristic” – the easiest thing to think about affects your conclusion.
Although heuristics often give good results, they sometimes do not. Therefore, Kahneman and Tversky argued that no, human cognition is not optimal. In fact, the English language has many more words with “k” in the third position than words starting with “k.”
Suboptimal or the best it can be?
In the 1980s, however, research began to emerge in the scientific literature, suggesting that human perception and cognition can often be optimal. For example, several studies showed that humans combine information from multiple senses – such as sight and hearing, or sight and touch – in a way that is statistically optimal, despite noise in the sensory signals.
Perhaps most importantly, research has shown that at least some cases of apparent suboptimal behavior are actually the opposite. For example, it was well known that people sometimes underestimate the speed of an object in motion. So scientists assumed that man’s visual perception of movement is suboptimal.
But recent research has shown that the statistically optimal sensory interpretation or percept is one that combines visual information about the speed of an object with general knowledge that most objects in the world tend to be stationary or slow moving. Moreover, this optimal interpretation underestimates the speed of an object when visual information is noisy or low quality.
Because the theoretically optimal interpretation and people’s actual interpretation make similar errors in similar circumstances, it may be that these errors are unavoidable when visual information is imperfect and that people actually perceive speeds of movement as well as they can be perceived.
Researchers found related results when they studied 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 perceptual example of visual speed estimation, 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 of how the world typically works. Researchers have found that the mistakes made by optimal strategies – unavoidable mistakes due to ambiguity and uncertainty – are similar to the mistakes people actually make, suggesting that people can perform cognitive tasks as well as they can be performed.
Evidence has grown that errors are inevitable when perceiving and reasoning with ambiguous inputs and uncertain information. If so, errors are not necessarily indicators of erroneous mental therapy. In fact, people’s perceptual and cognitive systems can actually work quite well.
Your brain, under constraints
There are often limitations to human mental behavior. Some limitations are internal: People have a limited ability to pay attention – you can not take care of everything at once. And people have limited memory capacity – you can not remember everything in detail. Other constraints are external, such as the need to decide and act in a timely manner. Given these limitations, humans may not always be able to perform optimal perception or cognition.
But – and this is the key point – even though your perception and cognition may not be as good as they could be, if there were no limitations, they could be as good as they could get the presence of those limitations.
Consider a problem whose solution requires you to think about many factors at once. If due to capacity constraints on attention you can not think of all factors at once, then you will not be able to think of the optimal solution. But if you think about as many factors as you can have in your mind at the same time, and if these are the most informative factors for the problem, then you will be able to think of a solution that is as good as possible given. your limited attention.
The limits of memory
This approach, which emphasizes “limited optimality,” is sometimes known as the “resource-rational” approach. My colleagues and I have developed a resource-rational approach to human memory. Our framework thinks of memory as a form of communication channel.
When you place an item in memory, it is as if you are sending a message to your future self. However, this channel has limited capacity and can therefore not transmit all the details in one message. As a result, a message retrieved from memory at a later time may not be the same as the message that was retrieved at the earlier time. This is why memory errors occur.
If your memory store cannot faithfully maintain all the details of stored items due to its limited capacity, then it would be wise to make sure that the details it can maintain are the important ones. That is, the memory must be the best it can be under limited circumstances.
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Researchers have actually found that people tend to remember task-relevant details and to forget task-irrelevant details. In addition, people tend to remember the general core of an object placed in memory while forgetting its fine details. When this happens, people tend to mentally “fill in” the missing details with the most frequent or common characteristics. In a way, the use of common features when details are lacking is a form of heuristics – it’s a quick and dirty strategy that will often work well, but sometimes fails.
Why did I remember eating chocolate cakes when I had actually eaten oatmeal raisin cakes? Because I remembered the core of my experience – eating cookies – but I forgot the fine details, and therefore filled these details with the most common properties, namely cookies with chocolate chips. In other words, this error shows that my memory works as well as possible under its limitations. And that’s a good thing.
Robert Jacobs, Professor of Brain and Cognitive Science, University of Rochester
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