Structures of Memory » Duration of Memory Stores

What you'll learn this session

Study time: 30 minutes

The three main memory stores: sensory, short-term and long-term memory
How long information stays in each memory store
Key research studies on memory duration
How to apply this knowledge to improve your own memory
Real-world applications of memory duration research

Duration of Memory Stores

Our memory isn't just one single system - it's made up of different stores that hold information for different lengths of time. Understanding how long information stays in each store helps us understand how we remember (and forget) things in our everyday lives.

Key Definitions:

Memory: The ability to encode, store and retrieve information.
Duration: How long information remains in a memory store before it fades.
Memory stores: Different systems in the brain that hold information for varying lengths of time.

📖 The Multi-Store Memory Model

In 1968, Atkinson and Shiffrin proposed that memory consists of three separate stores: sensory memory, short-term memory (STM) and long-term memory (LTM). Each store has a different capacity and duration.

⏰ Why Duration Matters

Understanding how long information stays in each memory store helps explain why we forget things quickly sometimes (like a phone number we just heard) but remember other things for years (like how to ride a bike).

Sensory Memory

Sensory memory is the first stop for all the information your senses pick up from the environment. It holds an exact copy of what you see, hear, feel, taste or smell.

Duration of Sensory Memory

Sensory memory has an incredibly brief duration:

Visual sensory memory (iconic): 0.5 seconds or less
Auditory sensory memory (echoic): 2-4 seconds

Because sensory memory lasts for such a short time, most information is lost almost immediately unless we pay attention to it and transfer it to short-term memory.

Research Study: Sperling (1960)

George Sperling conducted a classic experiment on iconic memory. He showed participants a grid of letters for just 50 milliseconds, then asked them to recall specific rows. Participants could only remember about 4-5 items, showing how quickly visual sensory memory fades.

This study proved that we see more than we can remember and that visual sensory information disappears very quickly if not transferred to short-term memory.

Short-Term Memory (STM)

Short-term memory is where we hold information we're currently thinking about or working with. Think of it like your brain's workspace or clipboard.

Duration of Short-Term Memory

Information in short-term memory typically lasts for about 15-30 seconds without rehearsal (repeating the information). If you actively rehearse information (like repeating a phone number), you can keep it in STM longer.

💡 Maintenance Rehearsal

Simply repeating information over and over (like saying a phone number repeatedly) can extend how long it stays in STM, but this information is easily lost if you get distracted.

📊 Displacement

When STM gets full (around 7±2 items), new information pushes out old information. This is why you might forget the beginning of a sentence by the time you reach the end of a long paragraph.

Research Study: Peterson & Peterson (1959)

In this famous study, participants were shown trigrams (three-letter combinations like "GHJ") and then asked to count backwards in threes from a given number (a distraction task to prevent rehearsal). When tested after various intervals:

After 3 seconds: 80% recalled correctly
After 18 seconds: only 10% recalled correctly

This study showed that without rehearsal, information in STM fades within about 18-30 seconds.

Long-Term Memory (LTM)

Long-term memory is our permanent storage system. It holds all our knowledge, experiences, skills and memories that last beyond the short term.

Duration of Long-Term Memory

The duration of long-term memory is potentially unlimited - information can be stored for a lifetime. Some memories from early childhood can be recalled decades later and skills like riding a bike can be retained even after years without practice.

🎓 Semantic Memory

General knowledge and facts can be stored indefinitely. For example, most people never forget how to read once they've learned.

🎮 Procedural Memory

Skills and procedures (like riding a bike or typing) can last a lifetime once fully learned, even with long periods of disuse.

📅 Episodic Memory

Personal experiences may fade over time but significant events can be remembered for decades, though details may become less accurate.

Research Study: Bahrick et al. (1975)

Researchers tested people's ability to recognise former classmates from high school yearbooks. They found that people could recognise about 90% of their classmates' faces even 15 years after graduation and around 60% after 48 years. This shows the remarkable duration of certain types of long-term memories.

Factors Affecting Memory Duration

Why Some Memories Last Longer Than Others

Several factors influence how long information stays in our memory stores:

Emotional significance: Emotionally charged memories tend to last longer in LTM
Elaborative rehearsal: Making meaningful connections to existing knowledge helps transfer information from STM to LTM
Retrieval practice: Regularly recalling information strengthens memory traces
Context: Information learned in multiple contexts is more likely to be retained

💻 Real-World Application: Studying

Understanding memory duration helps with effective studying. Instead of cramming (which only keeps information in STM), spaced repetition techniques help transfer knowledge to LTM. Reviewing material at increasing intervals (1 day, 3 days, 1 week, etc.) is more effective than studying everything at once.

🎯 Memory Improvement Techniques

To improve memory duration, try these techniques:

Break information into chunks (helps with STM capacity)
Create meaningful associations (helps transfer to LTM)
Use visual imagery (creates stronger memory traces)
Teach the material to someone else (deepens understanding)

Comparing Memory Stores

Duration Summary

Here's a quick comparison of how long information typically stays in each memory store:

Memory Store	Duration	Example
Sensory Memory	Less than 1 second (visual) 2-4 seconds (auditory)	The brief afterimage you see after a camera flash
Short-Term Memory	15-30 seconds without rehearsal	Remembering a phone number long enough to dial it
Long-Term Memory	Potentially unlimited (years to lifetime)	Remembering how to ride a bike even after years of not riding

Exam Tip 💡

When answering questions about memory duration in exams:

Always refer to specific research studies (like Peterson & Peterson or Sperling)
Be precise about the duration times for each store
Explain how information transfers between stores
Consider real-world applications and examples

🧠 Test Your Knowledge!