6.4. Memory Systems: Sensory, Short-term and Long-term Memories

According to the Stage Model, there are three memory systems: the Sensory Memory, the Short-term Memory, and the Long-term Memory. Each of these systems has different features and performs different functions with respect to the sensory inputs.

The Stage Model of memory, proposed by Atkinson and Shiffrin, divides human memory into three main systems based on the duration and capacity of stored information. The Sensory Memory captures all incoming sensory information for a very brief period, usually under a second; the Short-term Memory holds a limited amount of information for up to 30 seconds; and the Long-term Memory serves as a vast, permanent storehouse for information that can last a lifetime. Each system plays a critical role in how we process, retain, and retrieve memories.

Think of memory systems like a library. The Sensory Memory acts like the entrance where all incoming information is quickly glanced at (like browsing through new books), but only the books you find interesting (the information you pay attention to) get taken to the Short-term Memory, where you read them briefly (like checking out a book for a short time). Finally, the Long-term Memory is like the archive of the library where you can store entire shelves of knowledge for years.

The incoming information first enters the sensory memory. Sensory memory has a large capacity. However, it is of very short duration, i.e. less than a second. It is a memory system that registers information from each of the senses with reasonable accuracy.

Sensory Memory is the very first stage in the memory process, where all sensory input is held temporarily. It has a large capacity because it collects everything that our sensory organs detect—sounds, sights, smells, etc. However, this information is extremely fleeting; if not processed further, it fades quickly within less than a second. For instance, if you see a flash of light, you may still perceive its afterimage for a moment even after it has disappeared. This is due to the functionality of the sensory memory.

Imagine you're at a carnival, and you watch a fireworks display. The bright lights and loud sounds capture your attention. When the fireworks are over, you may still vividly recall the bright colors for a brief moment. This brief recall of the colors and sounds represents sensory memory at work, recording just enough to aid your understanding before it fades.

The second memory store called the short-term memory (abbreviated as STM), which holds small amounts of information for a brief period of time (usually for 30 seconds or less).

Short-term Memory is crucial for processing information we focus on. It has a limited capacity, typically around 7 items at once (plus or minus two), and it holds information for a maximum of about 30 seconds without rehearsal. This type of memory allows us to work with information in real time, such as remembering a phone number long enough to dial it. If the information in STM is rehearsed (either through maintenance rehearsal like repeating it to ourselves or elaborative rehearsal by connecting it to what we already know), it can sometimes be transferred to long-term memory.

Consider a situation where you're given a friend's phone number to remember. If you repeat the number over and over (maintenance rehearsal), you might be able to recall it long enough to dial it. However, if you associate the number with a memorable date, such as their birthday, you might help it stick in your long-term memory for future reference.

It has a vast capacity. It is a permanent storehouse of all information that may be as recent as what you ate for breakfast yesterday to as distant as how you celebrated your sixth birthday.

Long-term Memory is where data is stored on a more permanent basis. Unlike short-term memory, its capacity is virtually unlimited, and information can remain there for an entire lifetime. Long-term memories are generally encoded semantically, which means they are stored with context or meaning rather than just as raw data. This allows for efficient retrieval of information, although sometimes, we might forget things due to interference or inability to access the right retrieval cues.

Think of Long-term Memory as a vast bookshelf filled with books (pieces of information). Some books are new volumes (recent memories) like yesterday's lunch, while others are classics (old memories) that represent important events in your life, like your first day of school. Every time you recall a memory, it's like dusting off an old book and reading its contents again.

As suggested earlier, all informations which our senses receive are not registered; […] Only that information which is attended to enters the STM from sensory registers and in that sense, selective attention, as you have already read in Chapter 5, is the first control process that decides what will travel from sensory registers to STM.

Control processes are mechanisms that manage the flow of information between the different memory systems. The first among these is selective attention, which filters the incoming sensory information, allowing only what is deemed important or relevant to proceed to Short-term Memory. Other control processes include maintenance rehearsal, which helps retain information in Short-term Memory, and elaborative rehearsal, which integrates new information with existing knowledge for transfer to Long-term Memory.

Imagine you're at a crowded party trying to listen to your friend speak. Your mind has to filter out the noise and chatter around you to focus on their voice. This ability to filter out distractions and concentrate on your friend’s words is like selective attention, guiding important information (in this case, your friend’s conversation) into your Short-term Memory.

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