Features of Memory

Types of Memory

The four main different types of memory are probably not new to you. These are long-term memory (LTM), short-term memory (STM), sensory memory and working memory.

You are using LTM daily when you write, for example, because you learned how to write at a young age.

Fig. 1. An example of LTM is riding a bike.

You are using STM when you mentally repeat a list of groceries your mum just asked you to buy, for example.

You may have sensory memory when smelling a flower.

You are using your working memory when solving a mathematical equation.

The differences between the different memory types can be narrowed down when the memory features are explored. Memory has three main features:

1. Capacity refers to the amount of information that can be stored.
2. Encoding refers to the type of code that is used to transform information into memories.
3. Duration refers to the amount of time in which memory can be retrieved before it is forgotten.

Let's take a look at the features of both LTM and STM.

Features of Short-term Memory

The capacity of the STM system is small. Miller (1956) conducted a study in which he read participants a series of random numbers. The findings suggested that most people could only recall 5 to 9 digits. Even more, when participants were presented with pairs of numbers, they could recall 5 to 9 pairs. This suggests that information is grouped or chunked when stored, and short-term memory has a capacity of 7 (plus or minus 2) items.

In what relates to the encoding of STM, it has been suggested that STM encoding is acoustic. Such a conclusion was drawn from Wickelgren's (1965) study, in which he read out loud four letters to participants. To avoid rehearsal, Wickelgren asked participants to write down eight interference letters as a distraction task. The results indicated that when the interference letters were phonetically similar to the letters participants had to remember, participants made more mistakes. This, in turn, was evidence that information encoding is acoustic.

Peterson and Peterson researched the duration of STM in 1959. Participants in this study had to learn trigrams one at a time in intervals of 3, 6, 9, 12, 15 and 18 seconds.

After learning each trigram (and to avoid rehearsal), participants were asked to do a mental math exercise.

The results indicated that the shorter the interval between learning and recall was, the better the performance. After 3 seconds, around 80% of the trigrams were recalled, while after 18 seconds, only 10% were recalled. This was taken as evidence that the duration of this type of memory is of around 18 seconds, which can be described as short.

Features of Long-term Memory

It is difficult, if not impossible, to establish the capacity of LTM. Can you quantify all that you know? It is very hard. LTM capacity has been explained in terms of neuronal networks. Given that memories are dependent on neuron connections and that these cannot be unlimited, it is logical to conclude that LTM is not infinite. At the same time, the number of connections in our brains is enormous. Although psychologists acknowledge that there must be a limit to LTM capacity, they work based on the assumption that LTM capacity is unlimited, given its vast potential.

Fig. 2. Illustration of the unlimited number of neural connections in the brain.

The encoding of LTM is related to semantics. Baddeley (1966) conducted a study in which participants had to learn a list of words. The list could contain words similar in sound (e.g. hat, cap, rat, man, at) or similar in meaning (e.g. large, enormous, big, giant, huge). Twenty minutes after the learning phase, participants were asked to reproduce the list of words. The results showed that more mistakes were made when the words were similar in sound, suggesting that LTM encoding must be semantic.

The study of the duration of LTM has also been shown to be complex. While memories are stored for years, there is also information that cannot be recalled after hours. You may remember the name of someone you were introduced to two years ago, but you may not remember the name of someone you were just introduced to minutes ago. The duration of LTM is somewhat explained by theories of forgetting, for which you find a designated explanation.

As you probably realised from the studies reviewed, they use different ways to measure memory. The following section reviews the measurement of memory.

Measurement of Memory in Psychology

It is probably apparent that memory is not observable, although everyone can relate to it. The fact that it is not observable makes memory difficult to be measured. And because of this, psychologists have invested decades of research in developing tools to measure memory.

In experimental research, several paradigms have been employed to measure memory. Here we will review three:

1. Free recall and recognition is a paradigm widely used in memory research. It involves the presentation of lists of items, such as words, numbers or trigrams, that participants have to memorise. After some time, participants are asked to recall such a list, usually in any order. The more items participants remember, the better their memory is.
2. Priming is the method through which participants are given a list of words they must remember, for example, playground, hospital, three, mathematics, snack and pencil. During the testing phase, participants are given a list of parts of words. Following the example, the list would be following: pl, tal, the, ma, ck and pen. However, such a list would also include parts of words that have not been learned previously. Memory can be observed that primed words are recognised faster than other words
3. Last, there is the sentence verification paradigm. This involves stating sentences to participants and asking them to answer as fast as possible whether the sentences are true or false. An example would include researchers saying, "The sky is green", and a participant responding ", false". The faster the answer is given, the better the memory is consolidated.

Although the development of such paradigms has greatly benefited memory research, memory can also be assessed through memory tests. Let's move on to learn about the types of memory tests.

Types of Memory Tests Psychology

Memory tests are used to assess the memory abilities of individuals. Further, memory tests can detect potential memory difficulties or diseases, such as dementia.

The different psychological memory tests emerge based on the memory they measure. This way, there are tests for STM, LTM and working memory.

List of Memory Tests in Psychology

Here you will find a list of some memory tests and the type of memory they measure.

• WISC V (Wechsler intelligence scale for children) provides information about working memory, processing speed and auditory working memory.
• WPPSI-IV (Wechsler preschool and primary intelligence scale) can measure a child's working memory.
• WMRS (Working memory rating scale) can identify early working memory difficulties.
• BAS3 (British ability scale) assesses working memory.

• TOMAL-2 (Test of memory and learning) is used to measure verbal memory, non-verbal memory, composite memory, verbal delayed recall, sequential memory, free recall, and associative recall.
• WAIS-IV (Weschler Adult Intelligence Scale) provides information about the retention, processing and organisation of information.
• WMS-IV (Wechsler Memory Scale) measures auditory, visual, visual working, immediate and delayed memories