Structures of Memory

Structure of memory definition

Memory in psychology can be defined as a mental ability to encode, store and retrieve information. But why does some information stick, and some go in one ear and out of another?

Atkinson & Shiffrin (1968) proposed a model of memory that can account for the variability in memory processes. They posited that memory comprises several structures, each having its own characteristics.

Structure of memory examples

According to Multi-Store Memory Model, memory is not a unitary system. Instead, it consists of the sensory store, the short-term memory store (STM) and the long-term memory store (LTM).

Types of memory structure: Sensory store

The sensory store, also known as the sensory register, is where the sensory information from the environment is first processed. Everything we perceive through our senses at any given moment is filtered through this store.

The sensory register doesn't have a capacity limit, meaning it can store an unlimited number of sensory stimuli. Still, the duration for which information can stay there is very short. After a fraction of a second, the information is either transferred to the short-term memory store or is forgotten.

For the transfer to occur, we need to pay attention to the information. Only the information that is attended to can move to the STM store.

Types of memory structure: Short-Term Memory Store

The short-term memory store can hold information for around 18 seconds, but its capacity is limited to only about 7 (+/- 2) chunks of information. For information to enter this store, it needs to be encoded acoustically or in the form of words; this can occur through verbal or mental repetition.

When information is held in the STM, it is readily available for us to recall, we can also rehearse the information in our mind, so it stays in our memory for longer. This is called maintenance rehearsal.

Moreover, rehearsal allows the transfer of information to the long-term memory store. The information not sufficiently rehearsed is forgotten either because the store has reached its limited duration making (decay) or because of displacement. Displacement occurs when old information is replaced by new information.

Types of memory structure: Long-Term Memory Store

The memories we make throughout our lifetime are stored in the long-term memory store. Its capacity is thought to be unlimited, similarly to its duration. Encoding of information occurs semantically, which means information is stored based on its meaning. For the information to be transferred to our long-term memory, elaborative rehearsal is necessary.

Once the information is stored in the long-term store, we can bring it back to awareness, reminisce and think about it. However, as time passes, some memories will decay and be forgotten.

Structure and function of memory

The diagram illustrates how information flows through the stores in the multi-store memory model.

The multi-store model of memory diagram, StudySmarter Originals

Stages of memory in Psychology: encoding, duration and capacity

Let's summarise how different memory stores encode information, how long they can store information and how much information they can contain.

Evidence for the types of memory structure

There are several experimental research findings that are consistent with what Atkinson and Shiffrin (1968) predicted in their model.

Murdock's serial position curve study

Murdock (1962) presented 16 participants with lists of random English words. His lists varied in length, with the shortest having ten and the longest having 40 words. By the end of the list, participants were asked to write down all the words from the list that they could remember.

It was found that participants remembered the words at the beginning (primacy effect) and the end of the list the best (recency effect), while the words in the middle weren't remembered as well. This is called the serial position effect.

The study concluded that the primacy effect is likely due to participants having time to rehearse, so they moved to LTM. And the recency effect was due to the information not yet decaying from the STM store at the time of recall.

Murdock's findings support the existence of separate memory stores, one which keeps rehearsed information and one which keeps the recent information for a brief period.

Peterson & Peterson (1959) short-term retention study

Peterson & Peterson (1959) investigated the duration for which information can be kept in the short-term memory store when maintenance rehearsal is controlled.

They presented participants with a list of trigrams – combinations of three random consonants (e.g., WQB). Participants had to count back from a random number after seeing the list; this is a form of distraction task to prevent recall.

Researchers found that the number of trigrams that participants remembers decreased with time.

• After six seconds without rehearsal, participants only remembered 50% of trigrams, while after 18 seconds they remembered less than 10%.

It was concluded that the information in short-term memory decays after around 18 seconds.

The case study of Clive Wearing

The case of Clive Wearing was described by Wilson, Kopelman and Kapur (2008). Clive Wearing was a patient who developed global amnesia after a viral infection. He lost the ability to create new memories and forgot all the information stored in his long-term memory.

Wearing could still keep information in his short-term memory for a brief time but then would forget what had just happened after a few seconds had passed.

Clive's STM memory was preserved despite the neurological damage that caused LTM loss. His case suggests that STM and LTM rely on different memory stores, which supports the Multi-Store Memory Model.

Memory case studies such as that of Clive Wearing provide supporting evidence of the multi-store model of memory, freepik.com

Criticism of the Multi-Store Memory Model

Some aspects of the Multi-Store Model have been criticised. The capacity of short-term memory can differ depending on the person. Some people struggle to keep the seven chunks of information in their memory, while others can remember a few more. Therefore, it doesn't account for individual differences.

Alternative memory models have also proposed that the STM store does more than just storing and rehearsing. It is also thought to be capable of manipulating information to aid complex processes like problem-solving, reasoning, or planning.

Some critics argue that rehearsal is not always sufficient or necessary for the transfer of information. Some events from our past can be recalled for a long time despite not rehearsing them. On the other hand, sometimes we rehearse information, for example, to prepare for a test, and we still have problems recalling it later, suggesting the model may be too simplistic.

Evidence also suggests that the LTM store proposed by this model is oversimplified and that there are likely many types of long-term memories that are stored differently. This is exemplified by the case of Clive Wearing, who, despite losing his long-term autobiographical memory, retained his long-term procedural memory.