The Structure and Process of Memory
Memory as an Information-Processing System
Psychologists often describe memory using an information-processing model, similar to how a computer works. Information first arrives as input — what you see, hear, or otherwise sense. This input then goes through processing — the brain works on it, changes it, and decides what to do with it. Finally, the result of this work becomes output — what you produce, such as an answer, an action, or a spoken word. This three-stage system underpins everything psychologists study about memory.
Memory works as a three-stage system: input (information enters through the senses), processing (the brain works on the information), and output (the result is produced, such as an answer or action).
Encoding, Storage and Retrieval
Within this system, three key processes turn raw input into a usable memory. Encoding happens first — the brain converts what has been sensed into a code it can hold on to, such as a sound, an image or a meaning. Storage is what happens next: the coded information is kept in the system, ready to be used later. Retrieval is the final process — bringing the stored information back out when it is needed, whether that is recalling a name, an answer in an exam, or a fact learned years ago.
These three processes work together. If any one of them fails, the memory cannot be used successfully. Information that is never encoded properly cannot be stored; information that was never stored cannot be retrieved; and information that is stored but poorly organised can be very hard to retrieve, even though it has not actually been lost.
Sometimes information has been encoded and stored successfully, but retrieval still fails at that moment. This is why a fact can feel like it is “on the tip of your tongue” — it is there in storage, but something is stopping you from bringing it back out. This shows that encoding, storage and retrieval, while connected, are genuinely separate processes: a problem with one does not necessarily mean the others have failed too.
Short-Term and Long-Term Memory: Duration and Capacity
Psychologists compare memory stores using two features: duration and capacity. Short-term memory (STM) has a short duration — information fades quickly unless it is actively rehearsed — and a limited capacity, meaning only a small amount of information can be held at once. Long-term memory (LTM) works very differently: its duration can stretch across a whole lifetime, and its capacity is vast, able to hold huge amounts of information built up over years.
Think about the difference between remembering a phone number you have just been told and remembering your own home address, which you have known for years. The phone number sits briefly in short-term memory and disappears within moments unless you repeat it to yourself. Your home address has been transferred into long-term memory through repeated use over time, so it can be retrieved instantly, years later, without any conscious effort.
STM has a short duration and small capacity — information fades within moments unless rehearsed. LTM has a much longer duration, potentially lasting a lifetime, and a much greater capacity.
Retrograde and Anterograde Amnesia
Damage to the brain can disrupt these memory stores, producing amnesia. Retrograde amnesia affects memories formed before the injury or illness that caused the amnesia — the person struggles to recall things they knew or experienced beforehand. Anterograde amnesia works in the opposite direction — it disrupts the ability to form new memories from the point of injury onward, even though old memories from before may remain intact.
A person with retrograde amnesia may fail to recognise family members they knew well before their injury, or forget events, skills and facts they had already learned. A person with anterograde amnesia can usually still recall their life before the injury, but struggles to lay down brand new memories afterward — they might be introduced to someone and moments later have no memory of meeting them at all. The key distinction for exams: retrograde looks backwards to memories already formed; anterograde looks forwards, blocking the formation of new ones.
Some patients with severe anterograde amnesia can still hold a conversation normally, because information can pass briefly through short-term memory. The problem lies in transferring that information into long-term storage — moments later, the conversation itself is gone. This tells psychologists that short-term memory and long-term memory can be affected differently by brain injury, supporting the idea that they are genuinely separate stores within the wider memory system.
Why This Matters for Memory as a System
Amnesia is powerful evidence for psychologists because it shows that memory is not one single, unbreakable process. If encoding, storage and retrieval formed a single chain, brain damage would either wipe out all memory or none of it. Instead, amnesia can selectively damage the ability to form new memories while leaving old memories intact, or damage recall of the past while allowing new learning to continue. This supports the idea that different parts of the memory system — input, processing, encoding, storage and retrieval — can be affected separately by different types of brain damage.