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"Place one pound chopped watermelon, 1/2 cup pineapple juice, 1/2 cup white rum, 1/4 cup triple sec liqueur, and 1 tsp grenadine in the jug of a blender and blend until smooth."
This is the recipe for Watermelon Mai Tai. Simple, right? Yes, but only because your working memory enables you to keep several pieces of information in mind at the same time.
Your working memory is your mental workspace. When it functions as it should, it enables you to hold information in your mind for brief periods of time and manipulate that information mentally; for example, if given the numbers 8, 3, and 9, you can keep these digits in mind while adding them up without having to return to this page to double-check what digits you were given. If you cannot keep three single-digit numbers in mind for long enough to add them up, that's a clear mark of working memory problems.
Working memory impairments appear to lie at the core of Attention-Deficit/Hyperactivity Disorder or ADHD. According to DSM-V, a diagnosis of ADHD requires the presence of six or more of the following symptoms for six months or more: forgetfulness, absentmindedness, carelessness, short attention span, difficulties listening, difficulties following instructions, trouble organizing activities, and a disliking of tasks that take mental effort.
Do Learning Disabilities Have a Genetic Basis?
According to Tracy Alloway, a professor of education, working memory is a bit like a mental jotting pad, and how good your working memory is will either ease your path to learning and success or hinder it.
Alloway and her team conducted a large screening study of over 3,000 students. Of these, 10 percent were found to have working memory impairments that resulted in below age-expected performance on English and math tests, a poor attention span, forgetfulness, and difficulties following the teacher's instructions. The researchers hypothesize that differences in children's working memory are largely the result of differences in the children's genes and, hence, may not be correctible, at least not at a young age.
Newer research, however, undercuts a purely genetic explanation of differences in working memory abilities. For example, studies have shown that training the working memory capacity in children with ADHD may significantly reduce the risk of long-term learning disabilities and poor academic performance. It thus appears that proper training can correct working memory deficits, even at a young age.
The Effect of Training on the Capacity of Working Memory
In the 1950s, Psychologist George Miller conducted studies of the capacity of our working memory, suggesting that we can only hold between five and nine items in our working memory at any one time. An item in working memory can be a digit, a letter, or a tone, or a more complex pattern, such as the name of a friend.
Miller's findings that the maximum capacity of our working memory is nine items may seem surprising at first, as it would seem to predict that a U.S. phone number, including the area code, exceeds the capacity of our working memory.
This, however, is not quite true. While we cannot hold more than nine items in mind at any one time, if Miller's findings are right, we can hold indefinitely more complex items in mind by using a process called "chunking." For example, the six-letter string "FBICIA" may count as two items for someone capable of grasping "FBI" and "CIA" in chunks, and the eight-letter string "LOLXOSYS" may count as three items ("LOL," "XO," and "SYS") rather than eight for someone familiar with the newspeak brought about by the invention of the internet and texting.
Miller's studies of the capacity of working memory have been a major source of inspiration for future memory research and hypotheses about the mind. For example, they have been influential in developing the so-called global workspace model of the mind, according to which the mind contains an executive "desktop" with ever-changing, workable information spread across it.
In today's internet culture, perhaps an even more apt metaphor for working memory is that of an email inbox that never contains more than seven emails, plus or minus two, which you can then manipulate by answering them or completing the requested task.
Newer research has shown that Miller's magical number seven probably is too high. A more realistic estimate is that people can hold between one and four items in mind at any one time. The more recent findings have also shown that the capacity of working memory can be increased by practicing holding items in mind.
Psychologists Bopp and Verhaeghen, for example, found that the working memory capacity of participants subjected to memory training tasks over a five-day period had expanded their working memory capacity from one to four items. These findings suggest that there isn't a set limit to the capacity of working memory.
Other studies have yielded similar results. In one study, psychiatrist Klingberg and his colleagues recruited 53 children between the ages of 7 and 12 with ADHD and divided them into two groups. The children in the first group were given working-memory tasks that gradually increased in difficulty, and the individuals in the second group were given tasks that stayed at the same level of difficulty for the length of the trial. At the end of the study, the first group—the group whose working memory tasks had gradually become more difficult—performed significantly better than the second group on the final tests of their working memory.
Training Working Memory Repairs the Brain's Spam Filters Glitches
But the hypothesis that a "workout" for working memory enhances our ability to keep information in mind and manipulate it by making us capable of juggling more information is not the only one currently on the table. Another is that working memory "workouts" can prevent irrelevant information from interfering with information processing in working memory.
Neuroscientists McNab and Klingberg, for example, conducted a study in which they compared participants with poor working memory to individuals with especially good working memory. The volunteers were asked to remember items on a computer screen with different-colored squares while inside a brain scanner. The findings revealed that the areas of the prefrontal cortex in the front of the brain, which are involved in working memory tasks, became significantly more active during categorization-memory tasks in participants with particularly good working memory, but not in participants with working memory deficit.
These results suggest that training doesn't necessarily improve working memory by expanding its capacity, allowing you to hold and manipulate more items at the same time. Rather, training may improve working memory by reducing its capacity, at least when it comes to irrelevant information that interferes with the task at hand.
This, in turn, gives us good reason to think that working memory deficits needn't be the result of a limited working memory capacity but can also be the result of working memory allowing too much task-irrelevant information into the mental workspace. Like email spam, task-irrelevant information serves no function other than cluttering the mental workspace. An ultra-effective spam filter can prevent pointless clutter from filling up the mental workspace and distracting you from completing the task at hand.
Nowadays, even an ultra-effective spam filter won't quite do the trick when it comes to preventing our inboxes from filling up increasingly more quickly, eventually ending up becoming completely unmanageable. But without the spam filter, it would take you days rather than hours to delete the unnecessary information and allow you to manipulate the information that you were supposed to work with.
On this second way of explaining the benefits of a working memory workout, we can compare a poorly functioning working memory to a full and increasingly growing and cluttered email inbox, the kind of inbox that can prevent you from getting your work done.
There are thus two ways in which training can potentially improve your working memory. One is by increasing the capacity of your global workspace, thus allowing you to mentally juggle more items at the same time. As long as task-irrelevant information doesn't enter your mental workspace, your ability to work with more items at the same time can result in more efficient information processing.
The other way that a working memory workout can improve working memory is by fixing the glitches in the brain's spam filters, thus enabling your cognitive system to keep task-irrelevant information out of your mental workspace. With the distractors, you should be able to process information in your working memory more efficiently.
References
Alloway et al. (2009). The cognitive and behavioural characteristics of children with low working memory. Child Development, 80, 606-621.
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.
