Storing Memories
One of the most influential ways psychologists have studied memory is through the information-processing model, which compares the human mind to a computer. Like a computer, your brain:
- Receives input from the environment
- Processes and organizes that information
- Produces an output, such as a thought, decision, or action
The Atkinson–Shiffrin Model
Within the information-processing framework, Richard Atkinson and Richard Shiffrin (1968), proposed that memory moves through three distinct stages:
- Sensory Memory
- Short-Term Memory (STM)
- Long-Term Memory (LTM)
Their model (Figure 1) was the first to describe memory as a system of stages—much like information moving through a computer’s processors. Information (visual, auditory, tactile, etc.) enters from the environment, briefly lingers in sensory memory, moves into short-term memory if we pay attention to it, and may eventually be stored in long-term memory through rehearsal or meaningful processing.
Sensory Memory
In the Atkinson-Shiffrin model, stimuli from the environment are processed first in sensory memory: storage of brief sensory events, such as sights, sounds, and tastes. We are constantly bombarded with sensory information. We cannot absorb all of it, or even most of it. And most of it has no impact on our lives.
For example, what was your professor wearing the last time you saw them? Chances are, you don’t remember. Sensory information about sights, sounds, smells, and even textures, which we do not view as valuable information, we discard.
If light reflects off your cup of coffee hits your eye; the image is transferred through the optic nerve to the sensory register. If you do not attend to it, it fades from this memory store and is lost. In fact, your cup may be on your desk most of the time, and you see it without really “seeing” it many times during the day. If we view something as valuable, the information will move into our short-term memory system.
sensory memory
Sensory memory is the first and briefest stage of memory. It stores raw sensory input—what you see, hear, smell, taste, and touch—for only a fraction of a second to a few seconds.
Inconic and Echoic Memory
Visual sensory memory is known as iconic memory (from the word icon or “image).
Iconic memory was first studied by the psychologist George Sperling (1960). In his research, Sperling showed participants a display of letters in rows, similar to that shown in Figure X, “Measuring Iconic Memory.” However, the display lasted only about 50 milliseconds (1/20 of a second).
Then, Sperling gave his participants a recall test in which they were asked to name all the letters that they could remember. On average, the participants could remember only about one-quarter of the letters that they had seen.
Auditory sensory memory is called echoic memory, named after the phenomenon of an echo. Unlike iconic memory that tends to fade quickly, echoic memories have a longer lifespan and can persist for up to four seconds (Cowan, Lichty, & Grove, 1990).
This feature is beneficial in various ways, for instance, it enables you to recall the beginning of an extensive sentence when you reach its end, or to jot down your psychology professor’s last remark even after they’ve completed their sentence.
Short-Term Memory
Short-term memory (STM) is a temporary storage system that processes incoming sensory memory. The terms short-term and working memory are sometimes used interchangeably, but they are not exactly the same.
Short-term memory is more accurately described as a component of working memory. Short-term memory takes information from sensory memory and sometimes connects that memory to something already in long-term memory.
Short-term memory storage lasts 15 to 30 seconds. Think of it as the information you have displayed on your computer screen, such as a document, spreadsheet, or website. Then, information in STM goes to long-term memory (you save it to your hard drive), or it is discarded (you delete a document or close a web browser).
short-term memory
Short-term memory is a limited-capacity system that holds information you are currently using or thinking about. STM typically lasts 15–30 seconds unless you rehearse it.
For example, you are trying to remember a phone number that someone just gave you, so you begin repeating it to keep it in STM until you have a chance to write it down or dial it. However, if someone interrupts you to ask you a question while you are rehearsing the number, responding interferes with rehearsal, and the phone number is lost.
Short-Term Memory Practice
You may find yourself asking, “How much information can our memory handle at once?” To explore the capacity and duration of your short-term memory, have a partner read the strings of random numbers out loud to you, beginning each string by saying, “Ready?” and ending each by saying, “Recall,” at which point you should try to write down the string of numbers from memory.
Note the longest string at which you got the series correct. For most people, the capacity will probably be close to 7 plus or minus 2. In 1956, George Miller reviewed most of the research on the capacity of short-term memory and found that people can retain between 5 and 9 items, so he reported the capacity of short-term memory was the “magic number” 7 plus or minus 2. However, more contemporary research has found working memory capacity is 4 plus or minus 1 (Cowan, 2010). Generally, recall is somewhat better for random numbers than for random letters (Jacobs, 1887) and also often slightly better for information we hear (acoustic encoding) rather than information we see (visual encoding) (Anderson, 1969).
From STM to LTM: The Role of Rehearsal
Rehearsal moves information from short-term memory to long-term memory.
rehearsal
Active rehearsal (or maintenance rehearsal) is a way of attending to information to move it from short-term to long-term memory. During active rehearsal, you repeat (practice) the information to be remembered. If you repeat it enough, it may be moved into long-term memory. For example, this type of active rehearsal is the way many children learn their ABCs by singing the alphabet song.
Alternatively, elaborative rehearsal is the act of linking new information you are trying to learn to existing information that you already know. For example, if you meet someone at a party and your phone is dead but you want to remember his phone number, which starts with area code 203, you might remember that your uncle Abdul lives in Connecticut and has a 203 area code. This way, when you try to remember the phone number of your new prospective friend, you will easily remember the area code.
Levels of Processing
Craik & Lockhart (1972) proposed the Levels of Processing Model, which states that the deeper you think about something and the more meaning you can associate with it, the better you remember it.
Memory Traces
When memories are encoded and stored in the brain, they have to be stored somewhere, so the brain biochemically alters itself and its neural tissue. Just like you might write yourself a note to remind you of something, the brain “writes” what’s called a memory trace, or engram, changing its own physical composition to do so.
The basic idea is that events (occurrences in our environment) create a memory trace through a process of consolidation: the neural changes that occur after rehearsal to move a memory into long-term memory. Memory trace decay, when the physical record of a memory fades, and interference, memory obstruction caused by competing information, are two factors that affect short-term memory retention.
How long can you remember?
Peterson and Peterson (1959) investigated short-term memory using the 3 letter sequences called trigrams (e.g., CLS) that had to be recalled after various time intervals between 3 and 18 seconds. Participants remembered about 80% of the trigrams after a 3-second delay, but only 10% after a delay of 18 seconds, which caused them to conclude that short-term memory decayed in 18 seconds. During decay, the memory trace becomes less activated over time, and the information is forgotten.
However, Keppel and Underwood (1962) examined only the first trials of the trigram task and found that interference, where previously learned trigrams interfered with learning new trigrams, also affected short-term memory retention.
Long-Term Memory
long-term memory
Long-term memory is the system for storing information over long durations—from hours to decades. Its capacity is essentially unlimited. It holds information that is not in immediate use but needs to be remembered for an extended period of time.
How Is Long-Term Memory Organized?
Most researchers agree that memories are stored in semantic networks, where concepts are linked by meaningful associations (Collins & Loftus, 1975).
For example, hearing “peanut butter” may immediately activate:
- jelly
- sandwich
- lunch
- childhood memories
- American foods
This is spreading activation—one concept activates related concepts automatically. The more connections a memory has, the easier it is to retrieve.
Other Memory Models
The Atkinson–Shiffrin model was the first major framework to describe memory as a system of stages, and it remains useful for understanding the movement from sensory memory to short-term and long-term storage. However, psychologists have since developed additional models that refine, expand, or challenge aspects of this early approach. These newer models highlight that memory is far more complex than a simple three-stage pipeline.
Levels of Processing Model (Craik & Lockhart, 1972)
Instead of focusing on where memory is stored, the Levels of Processing model explains memory in terms of how deeply information is processed.
- Shallow processing (e.g., focusing on how a word looks or sounds) leads to weak, short-lived memory.
- Deep processing (thinking about meaning, making connections, applying information) produces more durable, long-term memories.
This model helps explain why elaboration, making personal connections, and studying with meaning-based strategies improve learning.
Tulving’s Long-Term Memory Systems
Endel Tulving argued that long-term memory is not one unified system, but several specialized systems supported by different brain networks:
- Episodic memory — personal experiences and autobiographical events
- Semantic memory — facts, concepts, and general knowledge
- Procedural memory — skills, habits, and motor abilities
This model is helpful for explaining why someone with amnesia may forget personal events (episodic memory) but still remember how to play piano or ride a bike (procedural memory).
Baddeley and Hitch Model of Working Memory (1974)
Baddeley and Hitch expanded on the idea of short-term memory by showing that it is not a single “holding tank” but a collection of specialized systems that actively work with information. They proposed that working memory includes:
- A phonological loop for verbal and auditory information
- A visuospatial sketchpad for visual and spatial material
- An episodic buffer that integrates information across senses
- A central executive that directs attention and manages all three systems
This model helps explain everyday experiences—such as why it’s harder to remember a phone number while someone is talking to you (two tasks competing for the phonological loop).
Connectionist/Parallel Distributed Processing (PDP) Models
More recent models view memory through the lens of neural networks. In connectionist models, memory is stored as patterns of activation across many interconnected nodes, rather than in separate “boxes” or stages.
- Learning strengthens the connections between nodes.
- Retrieval occurs when a pattern is reactivated.
This approach resembles how modern artificial neural networks learn and helps explain why memories can be fuzzy, reconstructive, and influenced by related knowledge.