This week in Memory & Cognition we’ll be talking about working memory and short term memory. Often these words are used interchangeably, but I’d argue the distinction between them is important. Short term memory refers to a brief “store” we have that lasts about 20-30 seconds. This store is limited (we usually consider it to be about 7 +/-2 – you know, like 867-5309 #sorryimnotsorry). Working memory, in contrast, is like a mental work bench, or like your mind’s CEO – directing you to pay attention to this or pull that from your long term memory. Usually, when we talk about STM, it is in the context of an experiment or lab. Working memory is what helps us get through the day.
Tomorrow, we’ll focus specifically on one part of our STM/WM: the phonological loop. Phonological loop refers to our verbal short term memory store and verbal working memory system. First, we’ll do a small experiment that demonstrates the limits of our verbal short term memory. In this experiment, students will view a series of letters and be asked to remember the string of letters. As the string of letters increases in length, it should become more challenging to remember all of the letters. Usually once we get to about 7 letters within the string, performance begins to falter. For example, if presented one at a time the following sequence
D
L
M
K
students will do quite well and easily be able to remember the sequence.
If, however, the are presented with a longer sequence (one at a time on slides) such as:
S
K
O
R
L
T
Q
M
A
F
Then it is likely that many students will fail to remember some or many of the letters in the sequence because the capacity of our STM store is exhausted and our working memory cannot manipulate that much information to hold in mind.
Then we’ll see ways in which we can somewhat remedy this limitation, via chunking. For example, if I present the following one at a time you might do okay at remembering the list, even though it is a long list:
B
A
T
D
O
G
C
R
O
W
This is much easier to remember because the letters form words, or chunks. Instead of holding in mind several individual letters you can hold the chunks in mind. This alleviates some of the stress on the verbal STM store.
Together, this demonstration shows that our STM is limited but it can be improved/increased via chunking. What’s more, it starts to demonstrate some evidence that this feat of memory is achieved through some sort of phonological loop, or verbal rehearsal system.
Additional evidence for a phonological loop comes from 3 findings: the phonological similarity effect, the word length effect, and the irrelevant sound effect. The first of these, phonological similarity, suggests that word lists that have confusable sounds are more challenging to remember than those that are more distinct (ex: cat, bat, hat compared to dog, cat, red). This indicates that our verbal working memory relies on a verbal rehearsal system like a phonological loop to store short term memories. The word length effect shows that as words become longer, our short term retention decreases (ex: short lists like those above, or using words such as “opportunity”). This is likely because it takes longer to vocalize or subvocalize the words stretching the 20-30 second storage limit of STM. Lastly, irrelevant sounds interfere with our STM – for example, listening to music that has vocals while studying can interfere with short term retention.
Our verbal STM can also be influenced by decay and interference, although primarily the latter. Decay simply refers to spontaneous forgetting that occurs over time. Interference refers to forgetting that occurs because of other material that impedes learning.
Why would we have adapted a phonological loop/verbal STM system?
In order to answer this question we need to consider what happens if this system is disrupted. For example, in patients with phonological loop deficits (due to brain damage), what happens?
Research suggests the primary role of the phonological loop is to facilitate word learning. For example, without the phonological loop, learning new words or languages is nearly impossible.
Wednesday…. We’ll continue this discussion and start to add to the phonological loop in considering our visuospatial sketchpad, the episodic buffer, and our central executive. In other words, we’ll see how our WM functions more wholly.
On Friday, we’ll get into the applications of WM. For example, WM correlates with many functions. Some evidence suggests it can be trained, but does this training transfer? We will consider this question.
More later…
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