Types of Memory

Memory is a process in which information is retained about the past:

Most psychologists agree that there are different types of memory: the sensory register, short-term memory (STM), and long-term memory (LTM). The three memory stores differ in duration (how long a memory lasts), capacity (how much can be held in the memory) coding (how much can be held in the memory) and coding (how information is stored, creating a ‘trace’)

Sensory Register:

1. The sensory register temporarily stores information from our senses (sight, sound, touch, taste and smell)- it’s constantly receiving information from around us.

2. Unless we pay attention, it disappears quickly through spontaneous decay- the trace fades.

3. The sensory register has a limited capacity, and a very limited duration (i.e. we can remember a little information for a very short time).

4. Information is coded depending on the sense that has picked it up e.g. visual, auditory or tactile

Short-Term Memory:

1. Short-term memory has a limited duration (i.e. we can remember a little information for a short time).

2. Coding is usually acoustic (sound).

Long-Term Memory:

1. Long-term memory has a pretty much-unlimited capacity and is theoretically permanent (i.e. it can hold lots of information forever). Coding is usually semantic (the meaning of the information).

2. There are different types of long-term memory:

   • Episodic memory stores information about events that you’ve actually experienced, such as a concert or a visit to a restaurant. It can contain information about time and place, emotions you felt, and details of what happened. These memories are declarative- this means they can be consciously recalled.

   • Semantic memory stores facts and knowledge that we have learnt and can consciously recall, such as capital cities and word meanings. It doesn’t contain details of the time or place where you learnt the information- it’s simply the knowledge.

   • Procedural memory stores knowledge of things such as walking, swimming, or playing the piano. This information can’t be consciously recalled.

Sperling (1960)- An investigation of the sensory register:

Method:

• In a laboratory experiment, participants were shown a grid with three rows of four letters for 50 milliseconds (0.05 seconds). They then had to immediately recall either the whole grid or a randomly chosen row indicated by a tone (high, medium or low) played straight after the grid was shown.

Results:

• When participants had to recall the whole grid, they only managed to recall 4 or 5 letters on average. When a particular row was indicated, participants could recall an average of 3 items, no matter which row had been selected.

Conclusion:

• The participants didn’t know which row was going to be selected, so it could be concluded that they would have been able to recall 3 from any row; therefore, almost the whole grid was held in their sensory register. They couldn’t report the whole grid because the trace faded before they could finish recalling

Evaluation:

• Because this was a laboratory experiment, it was highly scientific. The variables could be controlled, and it would be easy for someone to replicate the study. However, the artificial setting of the study means that it lacks ecological validity- people don’t normally have to recall letters in response to a sound, so the results might not represent what would happen in the real world.

Peterson and Peterson (1959)- The duration of STM:

Method:

• Participants were shown nonsense trigrams (3 random consonants, e.g. CVM) and asked to recall them after either 3, 6, 9, 12, 15 or 18 seconds. During the pause, they were asked to count backwards in threes from a given number. This was an ‘inference task’ to prevent them from repeating the letters internally.

Results:

• After 3 seconds, participants could recall about 80% of trigrams correctly. After 18 seconds, only about 10% were recalled correctly

Conclusion:

• When rehearsal is prevented, very little can stay in STM for longer than about 18 seconds

Evaluation:

• The results are likely to be reliable- it’s a laboratory experiment where the variables can be tightly controlled. However, nonsense trigrams are artificial, so the study lacks ecological validity. Meaningful or ‘real-life’ memories may last longer in STM. Only one type of stimulus was used- the duration of STM may depend on the type of stimulus. Also, each participant saw many different trigrams. This could have led to confusion, meaning that the first trigram was the only realistic trial.

Bahrick et al (1975) investigated LTM in a Natural Setting:

Bahrick et al (1975)- Very long-term memories (VLTMs):

Method:

• 392 People were asked to list the names of their ex-classmates. (This is called a 'free-recall test'.) They were then shown photos and asked to recall the names of the people shown (photo-recognition test) or given names and asked to match them to a photo of the classmate (name-recognition test).

Results:

• Within 15 years of leaving school, participants could recognise about 90% of names and faces. They were about 60% accurate on free recall. After 30 years, free recall had declined to about 30% accuracy.

  After 48 years, name recognition was about 80% accurate, and photo recognition was about 40% accurate.

Conclusion:

• The study is evidence of VLTMs in a 'real-life' setting. Recognition is better than recall, so there may be a huge store of information, but it's not always easy to access all of it — you just need help to get to it.

Results:

• This was a field experiment so it had high ecological validity. However, in a 'real-life' study like this, it's hard to control all the variables, making these findings less reliable — there's no way of knowing exactly why the information was recalled well. It showed better recall than other studies on LTM, but this may be because meaningful information is stored better. This type of information could be rehearsed (if you're still in touch with classmates, or if you talk to friends about memories of classmates), increasing the rate of recall. This means that the results can't be generalised to other types of information held in LTM.

Jacobs (1887)- The capacity of STM:

Method:

• Participants were presented with a string of letters of digits. They had to repeat them back in the same order. The number of digits or letters increased until the participant failed to recall the sequence properly.

Results:

• Most of the time, participants recalled about 9 digits and 7 letters. This capacity increased with age during childhood.

Conclusion:

• Jacobs concluded that STM has a limited storage capacity of 5-9 items based on the range of results. Individual differences were found, such as STM increasing with age, possibly due to the use of memory techniques such as chunking. Digits may have been easier to recall as there were only 10 different digits to remember, compared to 26 letters.

Evaluation:

• Jacobs’ research is artificial and lacks ecological validity- it’s not something you’d do in real life. Meaningful information may be recalled better, perhaps showing STM to have an even greater capacity. Also, the previous sequences recalled better, perhaps showing STM to have an even greater capacity. Also, the previous sequences recalled by the participants might have confused them in future trials.

Miller reviewed research into the capacity of STM:

1. Miller (1956) reviewed research into the capacity of STM. He found that people can remember about 7 items.

2. He argued that the capacity of STM is 7, plus or minus 2- ‘Miller’s magic number’.

3. He suggested that we use ‘chunking’ to combine individual letters or numbers into larger, more meaningful units.

   • For example, 2,0,0,3,1,9,8,7 is all the digits STM can hold. ‘Chunked’ into the meaningful recent years of 2003 and 1987, it’s much easier to remember.

STM could probably hold about 7 pieces of chunked information, increasing STM’s capacity.

Coding is about the way information is stored in memory:

1. In STM, we sometimes try to keep information active by repeating it to ourselves. This means it generally involves acoustic coding.

2. In LTM, coding is generally semantic- it’s more useful to code words in terms of their meaning, rather than what they sound or look like (although coding in LTM can also be visual or acoustic).

Baddeley (1966)- Investigating coding in STM and LTM:

Method:

• Participants were given four sets of words that were either acoustically similar (e.g. man, mad, mat), acoustically dissimilar (e.g. pit, cow, bar), semantically similar (e.g. big, large, huge) or semantically dissimilar (e.g. good, hot, pig). The experiment used an independent groups design participants were asked to recall the words either immediately or following a 20-minute task.

Results:

• Participants had problems recalling acoustically similar words when recalling the word list immediately (from STM). If recalling after an interval (from LTM), they had problems with semantically similar words.

Conclusion:

• The patterns of confusion between similar words suggest that LTM is more likely to rely on semantic coding and STM on acoustic coding.

Results:

• This is another study that lacks ecological validity. Also, there are other types of LTM (e.g. episodic memory, procedural memory) and other methods of coding (e.g. visual) that this experiment doesn't consider. The experiment used an independent group design, so there wasn't any control over participant variables