Memory - The capacity to retain information over time
STM - A temporary store where small amounts of information can be kept for brief periods. It is a fragile store and information can be easily lost
LTM - A permanent store where limitless amounts of information can be stored for long periods of time
Capacity - The amount of information that can be held in memory at any one time
Duration - the length of time that memories can be held
Encoding - The conversion of incoming information into a form that can be stored in memory
Storage - Maintaining information in memory over a period of time
Retrieval - The process of searching for stored information and bringing it to mind
Model - Theories of memory which are explained by researchers through the use of flow charts
Atkinson and Shiffrin (1968)
Most well known for the multi-store model
They proposed that information enters the system from the environment and first registers on the sensory memory store for a brie period of time before either daying or passing on to the STM. The STM has a very small capacity and information can be lost of not rehearsed. If the material is suffieciently rehearsed it passes on to the LTM
At each stage of the process , there are constraints (limitations) in terms of capacity, duration and encoding
Strengths - It provides evidence to support the distinction between STM and LTM
Weakness - The model is too simple and does not show the complexity of the memory
Study of STM and capacity of STM
If you read a list of 15 letters quickly, then cover them up and write them down in the same order, it will probably seem impossible. The second list same thing done again but the letters were split into five chunks and the groups of letters were not meaningful. The third list was also split into five chunks, but the groups of letters had meaning.
The capacity of STM is 7 + or - 2
Chunking combined letters or numbers makes them easier to remember
STM has a limited storage capacity of between five and nine items
Memory span can be increased by chunking
He experiemented with immediate serial recall of one-syllable, two-syllable and three-syllable words, and for two-word and eight-word phrases
Chunk size matters- smaller chunks are easier to remember than larger ones
The span as measured in chunks depends on the amount of information contained in the chunk
Participants had a shorter memory span for larger chunks than smaller ones
Bower and Springston (1970)
Participants were presented with a random letter sequence, and they were then asked to recall the sequence. They were then presented with another letter sequence, but were split into meaningful chunks.
People recall meaningful chunks rather than non meaningful chunks
The way things are chunked can improve recall
Strengths - A repeated measures design was used
Weaknesses - The amount of information that was presented was the same
Study of sensory memory: To find the capacity and duration of sensory memory
He used a chart containing three rows of letters, which he displayed for very brief exposures (50 milliseconds) to participants. They were asked to recall as many letters as possible and could usually recall 4 or 5, but were aware of more. Sperling changed procedure and trained participants to distinguish between 3 tones. He then exposed the chart for the same amount of time, but played the tones when the chart disappeared. Top row – high tone. Middle row – medium tone. Bottom row – low tone. On average participants recalled three items from whichever row had been cued the by tone.
The reason why participants can only recall 4 or 5 items in the whole report technique is because the image of the whole array fades during the time it takes to report back these items. Information in sensory memory is unprocessed. Information is passively registered in sensory memory (we cannot control what enters it). We then actively select certain items for transmission to STM by paying attention.
Strengths - It was a lab experiment and had a high level of control and it can be replicated with similar results (reliable) Weaknesses - The stimuli used were artificial and may not reflect how we use memory in everyday circumstances (the study might lack validity)
Glanzer and Cunitz (1966)
Study of STM and LTM: To look for distinctions between STM and LTM
Participants were presented with a list of words one at a time and tested on their free recall. There were two conditions:
1. Participants were asked to recall the words immediately after being presented
2. Participants were given a distracter task after being told the words and had to count backwards in threes for 30 seconds and then asked to recall the words
From condition 1 they had found the serial position curve. From condition 2 they found that the distracter task disrupted the recency effect and words from the last part of the list were not well recalled. The distracter task had replaced the last few words from the STM, but not affected the earlier words in the list as they had been rehearsed and passed into the LTM
Strengths - It was a highly controlled laboratory experiment and had been replicated many times
Weaknesses - The artificiality of the task means that it might not represent how memory works in everyday life
Bahrick et al (1975)
Study of duration in LTM: To study very long term memories in a real-life setting
There were three tasks: 1. In a free recall test 392 people were asked to list the names of their ex-classmates. 2. In a photo recognition task, participants were shown photos of ex-classmates and asked if they could remember the names. 3. In a name recognition task, participants were given names of their ex-classmates and asked to find the matching photos.
Within 15 years of leaving school, participants were 60% accurate in free recall and could recognise 90% of faces and names. Within 48 years, participants were 30% accurate in free recall and could recognise 75% of faces and names. Free recall memory had declined more than more than photo and name recognition.
Strengths - It has a high level of mundane(everyday) realism: remembering faces is a task relating to real-life settings
Weaknesses - Class mates faces and names are a very particular type of memory information, they may have emotional significance and there will have been opportunity for a great deal of rehearsal, given the daily contact class mates will have experienced. This is not true for other types of information
Study of capacity in STM
Participants were presented with strings of letters or digits and were asked to repeat them back in the same order. The length of the string was increased, from three to four to five etc, until the participant was unable to repeat the sequence accurately.
On average, participants recalled nine digits and seven letters. The average recall increased with age. STM has a limited storage capacity of between five and nine items, but learned memory techniques (e.g. chunking) may increase capacity as people get older. Since there are 26 letters in the alphabet but only 10 digits (0-9) letters may be harder to recall.
Strengths - Later studies (Miller 1956) have supported Jacobs’ findings
Weaknesses - The research is artificial. In real-life settings people do not usually need to remember strings of meaningless numbers or letters, and the research therefore has a low ecological validity
Investigating encoding in STM and LTM: To look at the effects of acoustic and semantic encoding on recall from STM and LTM
Participants were given four sets of words from the following groups: acoustically similar, acoustically dissimilar, semantically similar and semantically dissimilar. They were asked to recall as many words as possible, either immediately or after 20 minutes.
In immediate recall situation (from STM), participants had more difficulty remembering the acoustically similar words. In the delayed reaction condition (from LTM), participants had more difficulty remembering the semantically similar words. The difference in the difficulty suggests that STM relies on acoustic encoding while LTM relies on semantic encoding.
Strengths - It was a lab experiment and he used familiar words rather than consonants
Weaknesses - The research is artificial; in a real-life setting people do not need to remember a string of words and therefore has low ecological validity.
Peterson and Peterson (1959)
To study the duration of STM: To find out how long items would remain in STM without rehearsal
Participants were presented with a consonant trigram (e.g. CKF). They were then asked to count backwards in threes from a specific number, to stop them rehearsing the trigram. This procedure was repeated several times using different trigrams on each presentation.
Participants were able to recall about 80% of trigrams after a 3-second interval without rehearsal. Recall became progressively worse as the intervals lengthened, until after 18 seconds, they recall fewer than 10% correctly. Information disappears or decays very rapidly from STM when rehearsal is prevented.
Strengths - The lab experiment was carried out in controlled conditions. This study used a repeated measures design to avoid individual differences
Weaknesses - Trigrams are artificial things to remember - not be a good way of testing how we remember things in everyday life. It is possible that the loss of information was more to do with capacity limitations than duration. The trigrams may have caused proactive interference (confusion) and so later trigrams are incorrectly recalled
To investigate the nature of coding in STM
Participants were presented with a random sequence of six consonants. He projected them in a very rapid sequence on to a screen. There were two conditions: 1. The letters were acoustically similar. 2. The letters were acoustically dissimilar. Immediately after the presentation, participants were asked to write the letters down in correct serial order.
Conrad found that participants frequently made errors of recall. The majority of errors involved the substitution of a similar sounding letter. Participants found it more difficult to recall strings of letters that sounded the same than letters that sounded different. We must convert visually presented material to an acoustic code in STM and that we then find it difficult to distinguish between words that sound the same e.g. there is acoustic confusion.
Strengths - It was a well controlled lab experiment
Weaknesses - It used artificial stimuli – we do not have to remember strings of consonants in everyday life. He used students as his participants who might not be representative of the general population
Sensory memory - A set of limited capacity, modality-specific stores that hold information for a very brief period of time
Iconic store - Visual input (things we see)
Echoic store - Auditory input (things we hear)
Hapatic store - Tactile input ( things we touch)
Basic reasons for forgetting
Encoding failure - Information did not get into memory
Storage failure - Information has disappeared from memory and is no longer in storage
Retrieval failure - Information is stored in memory but it cannot be located
Two major theories of forgetting
Decay theory - Information in memory eventually disappears if it is not used
Interference theory - Information stays in memory permanently even if it is not used. Forgetting occurs because other things we have learnt somehow prevent us from finding the information we want
Duration - Very limited
Encoding - mainly sound (acoustic)
Forgetting - Mainly displacement
Duration - Unlimited
Encoding - mainly by meaning (semantic)
Forgetting - Mainly interference
Neuropsychological evidence for STM / LTM
Strongest evidence for a distinction between STM and LTM come from the study of people who have suffered from brain damage. The loss of memory among such people is usually selective, e.g. it affects one type of memory but not another.
People with Alzheimer's disease have been found to have low levels of the neurotransmitter acetycholine. This shows that acetycholine might have an important function in LTM.
Modern brain-scanning techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) scans have provided more support for the existence of two separate memory stores.
The case of HM
He underwent brain surgery to remove parts of his temporal lobes and hippocampus. The operation left him with severe memory deficits, although his IQ remained above average. He was able to recall events in his early life but was unable to remember events for about ten years before the surgery and could not learn or retain new information. This suggests that HM had a normal STM but his LTM was now defective.
Shallice and Warrington (1970)
The case of KF
A young man sustained brain injuries after a motorcycle accident. He appeared to have his LTM intact in that he was able to learn new information and recall stored information, however his STM was affected so that he had a recency effect of only one item.
Drachman and Sahakian (1979)
Investigated the effects of acetycholine
They administered a drug to a group of participants that blocks the action of acetycholine in the brain. The gave the participants various memory tasks that tested either STM or LTM and compared them with a controlled group
The experimental group performed at normal levels on the STM taks, but poorly on LTM taks
This shows that STM and LTM work as separate stores
Squire et al (1992)
Found that the hippocampus is active in LTM tasks whereas areas in the prefrontal cortex are activated for STM tasks.
Beadsley et al (1997)
Showed that the prefrontal cortex of the brain was active when participants were involved in STM tasks.
Factors that affect the capacity of STM
Influence of LTM
Factors that affect the duration of STM
Intention to recall
Amount of information to be recalled
Strengths of the multi-store model
It has made an important contribution to memory research. The information-processing approac has enabled psychologists to construct testable models of memory and provided a foundation for later important work
Weaknesses of the multi-store model
The model is over-simplified and fails to reflect the complexity of human memory.
It does not take into account that different types of things we have to remember.
Much of the supporting evidence for the MSM comes from artificial, laboratory studies, which might not reflect how memory works in everyday life.