Short-Term Memory

Imagine you’re staying over at a friend’s place for the first time. You get a brief tour, are shown to the guest room (or the couch), and quickly find yourself asking, “What’s the Wi-Fi password?” Your friend points you in the direction of the router, and you quickly memorize the nonsense string of numbers and letters before heading back to your laptop on the coffee table. You’re able to maintain the information for long enough to type it in, but you’ll probably have forgotten it completely a couple of hours later. 

The cognitive system that allows us to store newly learned information for a brief period of time is called short-term memory. Even though short-term memory is often colloquially used to refer to memories lasting up to days or weeks, it actually only encapsulates information retained for about 30 seconds; anything beyond that is considered to be long-term memory.^1,2 Also called “active memory” or “short-term storage,” short-term memories are considered “easily accessible”—meaning they take little effort to remember—but can be lost just as quickly if we don’t transfer them to long-term memory through repetition or review, a process called consolidation.³

In the human brain, memory isn’t just one operation, but a series of related stages that work together to process information and store it for later use. Memory stages are often defined by their capacity (how much information can be stored at once) and duration (how long they can hold it).^1,2 The first stage is sensory memory, which processes highly detailed sensory information for as short as a few milliseconds, like the brief afterglow of a flash of light.² Information can then be transferred to short-term memory, which has a limited capacity and duration. For example, you’ve probably noticed that a longer Wi-Fi password is more difficult to memorize than a shorter one, and it’s easier to remember it 10 seconds later than it is two days later. Consolidation can transfer short-term memories into long-term storage, which has an indeterminate capacity and indefinite duration—that’s why we can probably remember several childhood birthdays years or decades later.¹ 

The information that moves from sensory memory to short-term memory is decided by several factors, one of which is attention; we might not notice the sound of a bird chirping if we’re at work, but we’re more likely to remember it if we’re birdwatching, for example. Similarly, the consolidation of short-term memories depends on rehearsal and review, time, and even sleep.³ In each transition between memory stages, whether it be from sensory to short-term memory or short-term to long-term memory, information can either be forgotten or retained depending on our goals, attention, and active behaviors such as repetition. As annoying as it can sometimes be, forgetting memories is a normal and necessary process built into our memory systems. By only holding on to details that we’ve consciously reviewed or that help us achieve our goals, we can process information more purposefully and efficiently.