Memory is a complex cognitive function that not only allows us to remember where we have left our house keys but also our life experiences, to distinguish the people we love from the strangers and even to remember who we are and what we like.
Short-term memory plays an essential role in the memory process since it is at the base of learning and problem solving, allowing us to retain information for a short period of time, but enough to link the data and give them a logic. Thanks to short-term memory we can maintain a coherent conversation or follow the steps of a recipe, for example. However, do you know how long that kind of memory actually lasts?
The patient who allowed us to determine how long short-term memory lasts
For Psychology, the term “short term” is really a very short period of time, so there is some consensus that short-term memory lasts between 15 and 30 seconds. It lasts not days, hours, minutes, but only 15-30 seconds.
How has it been determined?
Cognitive psychologists established that short-term memory is only maintained for a range of 15 to 30 seconds after analyzing patients who have suffered from amnesia. The first documented patient to show profound long-term memory loss with intact short-term memory was named Henry M.
He was treated for epilepsy when he was 20, in the 1950s. At that time, doctors removed a part of his brain trying to cure him of seizures. Although the epilepsy improved, he suffered serious consequences: he lost the ability to form new long-term memories. During the 40 years that he lived after his surgery, Henry M. did not form any significant new memories of his life.
Henry M. did not remember what he had done the day before and did not recognize the doctor who treated him during those 40 years, but he could remember a phone number and repeat it to another person, as well as carry on a relatively normal conversation since he retained the information for a few brief seconds in his memory before it disappeared.
Neuroscientist Suzanne Corkin compared memory to a hotel. We can see short-term memory as the lobby and long-term memory as the guest rooms. She wrote: “Information is collected in the hotel lobby of Henry’s brain, but cannot be recorded in the rooms.”
Other studies carried out with patients with anterograde amnesia and people with intact memory have confirmed that short-term memory lasts between 15 and 30 seconds.
Fragmentation, the technique to improve working memory
The brevity of short-term memory also explains why it is so difficult for us to remember a series of numbers for very long unless we repeat them over and over again in our minds. That repetition updates short-term memory, which deteriorates rapidly, so that its content vanishes after 30 seconds if we can’t store it in long-term memory.
In this sense, a study carried out at the Institut d’Investigacions Biomèdiques August Pi i Sunyer suggested that short-term memory activity is very fragile and begins to degrade after the first 10 seconds. However, these researchers hypothesize that short-term memory activity does not simply disappear, but diffuses into the neural network, so that in the end the memory is different and distorted. In practice, it would not be a loss in the strictest sense of the term, but rather that the neurons that are at the base of short-term memory lose their stability and the information fades if it does not go to long-term memory.
However, it has also been appreciated that people with a higher IQ are capable of retaining more information in their short-term memory. There is a simple technique called “Chunking” that serves to expand the amount of data we can store in our short-term memory.
One method of improving our ability to remember data for a short period of time is to chunk that information; that is, organize it into meaningful sections. For example, it is easier to remember 9 numbers if we divide it into 3 groups of 3. It is also easier to remember a long number by dividing it into shorter sections, as we usually do with telephone numbers.
In general, the average persons under normal conditions should be able to hold an average of 4 items in their short term memory. However, if you apply the fragmentation technique, you can remember much more.
Sources:
Barbosa, J. et. Al. (2020) Interplay between persistent activity and activity-silent dynamics in the prefrontal cortex underlies serial biases in working memory. Nature Neuroscience; 23: 1016–1024.
Monuszko, K. (2014) Permanent Present Tense: The Unforgettable Life of the Amnesic Patient, H.M. J Undergrad Neurosci Educ; 12(2): R3–R4.
