Introduction to my Project, the Basics of Working Memory, and Digit Span

Welcome to my blog. My name is Adam and I am a senior at Basis Flagstaff. For the next 2-3 months, I will be studying the short-term effects of an hour-long exercise session on working memory or short-term memory with Dr. Birkett PhD of NAU and my Basis advisor and biology teacher, Sheri Jordan.


My interest in psychology started during my sophomore year when I took AP psychology. I primarily took the class because I heard the AP exam was straight forward and relatively easy. Little did I know that I would quickly start to enjoy the class and learning about psychology in general. One of the more interesting topics we covered was memory because of how impressionable and inconsistent it can be.


Fast forward a few years and I have come across the opportunity to study memory and how it can be influenced in a real-world environment. Dr. Birkett originally constructed the study to look at how weekly, hour-long exercise sessions would affect working memory over the course of many weeks. However, I will be studying how exercise affects working memory immediately after a weekly session.


So how can we observe these differences in working memory? Well, there is a psychological test called digit span that can measure just how well a person can use their working memory. To conduct a digit span test, you give the subject sets of one-digit numbers and they attempt to recite them back to you. The first few sets start off with only 3 numbers. If they are recited correctly to a certain degree, the subject can move on to reciting back sets of 4 numbers. As they continue to recite sets correctly, the amount of numbers they have to recite increases. This is where two fundamental rules of working memory come into play.


The first one is the rule of 7 ± 2. It says that our brains can only process between 5 and 9 pieces of information at a time. This number varies based on what kind of information is being processed. It is harder to remember 7 types of fruits or colors than 7 digits. This is true not only because digits are a simpler thing to remember, but also because we tend to group digits. A common example of digit grouping is phone numbers where we group the first 3 digits and the last 4 digits (ex. 778-4433). I experienced this first-hand when I took the digit span test for the first time. I struggled to recite the sets of 8 digits, but successfully recited a set of 9. This is because it's not as hard to remember 3 groups of 3 numbers as opposed to one group of 9.


The second psychological rule is called the serial position effect. It says that we tend to memorize the first and last items in a list more easily than the ones in the middle. The reason why we remember the first items better has to do with what we are subconsciously doing when we are listening to the items being read out. When we are given each additional item to remember, we try to quickly recite the items we have already been given. For example, if I have just heard the 4th number out of 9, I will quickly try to recite the first 4 numbers in my head right before I hear the 5th. While this method works early on when you only have to recall a few numbers, it doesn't work as well when you have to think of the last 7 numbers right before you hear the 8th. Every time that we do these mental recitals we hear the same few numbers from the start of the list in our head and this solidifies them in our memory. The last items that are given to us are remembered easier simply because they are fresh in our memory. When we analyzed my performance on the digit span, the serial positioning effect was clearly there. The digits that I got wrong in the lists tended to be in the middle of the lists. The graph below illustrates the serial positioning effect in action.

In this example, subjects were given lists of 7 words to memorize. They memorized the first word about 75-80% of the time. The 3rd, 4th, and 5th words were recalled less than 50% of the time. The subjects could recall the last word about 70-75% of the time. 








The best way to conduct a digit span test is by implementing it through a computer program called PEBL. This is because a computer can read out a list of numbers at a consistent rate, volume, and tone of voice whereas a researcher might need to catch their breath between numbers giving the subject more time to recite. It also automatically randomizes the digits so the researcher doesn't need obtain randomized number lists before the study. On top of this, PEBL will organize the data of each trial neatly in a spreadsheet so it can be analyzed immediately after a subject completes the digit span. All the researcher has to do is set variable controls such as how much time is given between the reading of one digit to the next. Once that is done, the same exact test can be given to subjects however many times is needed.


Once I program a digit span test, I will be testing subjects immediately before an exercise session and immediately after. Then I will be comparing the results of the two to see if their performance changed in multiple ways. One of those ways is simply looking at how many lists were successfully memorized. I can also look at how long it took subjects to enter the numbers back into the program in milliseconds and which numbers within a list were entered in wrong to see if serial positioning is affected. PEBL observes the trial in many ways and they can all be looked at to see not only if working memory improves, but also if there is any change in the way subjects use their working memory to memorize the lists such as different uses of grouping.


In addition to the digit span test, I can use the reverse digit span. In this test, subjects are asked to recite the numbers in reverse order. For example, if they are given the digits 9 2 8, they are supposed to enter them back into the program as 8 2 9. The reverse digit span can give us a better idea of how working memory is affected and this is due to the inherent difference between working memory and short-term memory.


As psychologists conducted similar experiments in the past, they realized that short-term memory had a lot to do with how we process information that we are given in a short period of time. As time passed, short-term memory became known as working memory because the name reflects how our brain is processing information instead of just memorizing it. In the case of digit span versus reverse digit span, a regular digit span test only has subjects memorize a list while a reverse digit span has them memorize a list, and then process that list to recall it backwards. It's a task that is more involved and it encapsulates the idea that working memory is about memorizing and processing information in a short period of time.


As I gather more data by implementing the two digit span tests, I can look at how performance improves after a workout. I can also look into how this improvement changes over multiple workout sessions.


For now, I am taking a CITI ethics course to be able to carry out this study. I am also starting on writing an IRB amendment that will allow me to join Dr. Birkett's study once it is approved.


Thank you for reading and joining me as I update my blog every week to tell you about how my senior research project is progressing.