Memory

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Short-term memory (STM)

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Your memory for immediate events. Has limited duration and limited capacity.

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Long-term memory (LTM)

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Your memory for events that have happened in the past. Lasts anywhere from 2 minutes to 100 years. Has potentially unlimited duration and capacity (in a healthy mind).

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Duration

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A measure of how long a memory lasts before it becomes unavailable.

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Studies on the duration of memory

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1. Peterson and Peterson (1959) - Duration of STM
2. Bahrick et al (1975) - Duration of LTM
3. Nairne et al (1999) - Duration of STM

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Peterson and Peterson (1959)

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- 24 students attending their university and each participant was tested over 8 trials
- Each trial: participant was given a consonant syllable and a three-digit number eg. TXH 512
- They were asked to recall it after a retention interval of 3, 6, 9, 12, 15, or 18 seconds
- During the retention interval they had to count backwards from their 3 digit number

RESULTS:
- Participants were 90% correct after 3 seconds
- 20% correct after 9 seconds
- 2% correct after 18 seconds

Suggests:
STM has a very short duration, less than 18 seconds, if verbal rehearsal is prevented

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EVALUATION:
Peterson and Peterson (1959)

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x Lacked ecological validity - stimulus material was artificial
x Findings may be explained by displacement rather than the material only lasting a short time in STM
x Small sample size
x Participants may guess aims of study - possibility of demand characteristics
x Contradictory evidence - Nairne et al (1999)
+ Opened door for further investigation into duration of memory

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Bahrick et al (1975)

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- Tested 400 people ages 17-74 on their memory of classmates
- Various tests: photo-recognition test and free-recall test included

RESULTS
- Participants who were tested within 15 years of graduation were about 90% accurate in identifying faces
- After 48 years, this declined to about 70% for photo recognition
- Free recall was about 60% accurate 15 years, dropping to 30% after 48 years

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EVALUATION:
Bahrick et al (1975)

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x Results may be due to rehearsal
x Investigator bias
+ Quite large, varied sample (range of ages)
+ Range of tests

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Nairne et al (1999)

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- Modified the Peterson's technique so that the material to be remembered was the same across trials (to prevent one set of items interfering with another)
- Participants were shown 5 nouns and after a retention interval were shown them in a different order and had to recall them in the correct order

RESULTS
- Found that items could still be accurately recalled after as long as 96 seconds

SO...
Seems that info. remains for longer in STM if there is no interference from other items

x Words instead of syllables - participants may have remembered these easier

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Capacity

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This is a measure of how much can be held in memory. It is measured in terms of bits of information such as number of digits.

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Encoding

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The way information is changed so that it can be stored in memory (after being entered via the senses).

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Chunking

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Miller proposed that the capacity of STM can be enhanced by grouping sets of digits or letters into meaningful units or 'chunks'.

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Studies on the Capacity of Memory

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1. George Miller (1956) - Capacity of STM
2. Jacobs (1887)
3. Simon (1974)

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George Miller (1956)

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- Made observations that everyday things come in 7's e.g. 7 days of the week, 7 notes on musical scale
- Also reviewed several studies that have investigated the span of STM e.g. where participants counted dots flashed on a screen or were tested on the recall of words

RESULTS
- Participants accurate with 7 dots counted on the screen but very inaccurate when 15 dots shown
SO...
Capacity of STM is about 7+-2 (chunks)

- He also observed that people can recall 5 words as well as they can 5 letters - chunking

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EVALUATION:
Miller (1956)

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x Chance of investigator bias - relies heavily on his own interpretation
x Miller may have overestimated capacity of STM - not scientific
x Relatively dated study - unsure of how much control on variables
+ Real-world applications - UK Postcode system (Baddeley has done research to back this up)

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Jacobs (1887)

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- Tested digit span
- Each participant first listened to 4 digits and had to recall these in the correct order. If they got the order right then they progressed to 5 digits and so on, until they couldn't recall it correctly. This determined their digit span.
- Same activity was repeated with letters

RESULTS
- Mean span - digits = 9.3
- Mean span - letters = 7.3
- Digit span increased with age. 8 year old's average = 6.6 digits, 19 year old's = 8.6 digits

MAY BE BECAUSE....
People develop strategies to improve their digit span as they get older such as chunking.

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EVALUATION:
Jacobs (1887)

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x Very old study - may not have been very well controlled
+ Range of ages shown - generalisable

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Simon (1974)

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- Tested his own recall for one-syllable, two-syllable and three-syllable nouns and also familiar phrases
- He read them aloud and then later tried to see how many he could recall

RESULTS:
- Slightly shorter span for three-syllable words than one- or two-syllable words
- Found that there was a shorter memory span for longer phrases than shorter phrases

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EVALUATION:
Simon (1974)

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x Lacks generalisability - only one person involved
x Investigator bias - up to his own interpretation

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Encoding

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The way information is changed so that it can be stored in memory. It enters via the senses and then stored in different forms such as visual codes (picture), acoustic forms (sounds) or a semantic form (meaning).

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Free Recall

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A method of testing memory. Participants have to remember a list and are asked to recall the items by writing as many as they know down in any chosen order.

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Retention Interval

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The period of time during which you have to remember something.

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Articulatory Suppression task

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An activity that prevents rehearsal of words in the articulatory loop.

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Studies on Encoding in Memory

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1. Baddeley (1966a and b)
2. Brandimote et al (1992) - STM
3. Frost (1972) - LTM

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Baddeley (1966 a and b)

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- Group A participants were given acoustically similar words e.g. cab, can, mad, max
- Group B were given acoustically dissimilar words e.g. pit, few, cow, pen
- Group C given semantically similar words e.g. great, large, big, huge
- Group D given semantically dissimilar words e.g. good, huge, hot
- On each trial 5 words were read out
- After a time interval, participants were shown 10 words and were asked to select the correct 5 words and place them in the right order

RESULTS:
- When STM tested - participants with acoustically similar words had lowest recall
SUGGESTS: words in STM are encoded acoustically
- When LTM tested (time interval of 20 mins) - group with semantically similar words had lowest recall
SUGGESTS: words in LTM are encoded semantically

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EVALUATION:
Baddeley (1966)

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x Quite artificial stimuli were used - should be cautious when generalising the results
i.e. - if info is meaningful, they may use semantic encoding even for STM tasks
x LTM task was not very long term (not very realistic)
- 20 mins not the same as remembering over months and years
- possible that different kinds of encoding processes are involved when info is stored over months and years

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Brandimote et al (1992)

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- Showed participants 6 picture pairs
- One of each pair was a component of the other
- Participants were asked to 'subtract' the second picture from the first one for each pair
- During the retention interval, some participants had to say 'la la la' to prevent any verbal rehearsal (an articulatory suppression task)

RESULTS:
- Performance was unaffected by the articulatory suppression task
SO... images were visually rather than verbally encoded
- encoding in STM not always acoustic
- Normally, we 'translate' visual images into verbal codes in STM - HOWEVER since verbal rehearsal was prevented in this study, visual encoding was used

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EVALUATION:
Brandimote et al (1992)

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+ Research support - Wickens et al (found that sometimes used semantic encoding) and Frost

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Frost (1972)

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- Visual encoding in LTM
- Participants were shown drawings of 16 common objects
- After a 15 minute interval, participants were tested on recall of the drawings and their responses were timed
- In some cases, the original drawing was presented in a different form - from a slightly different perspective

RESULTS:
- Participants responded more quickly when the drawings were identical to the original presentation
SHOWS... they encoded drawings visually

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EVALUATION...
Frost (1972)

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x Speed of response was important
- When people are required to make quick decisions, this affects the kind of information recalled
- Hintzman and Curran found that quicker responses make people more dependent on recognition (visual in Frost's study) than recall (semantic)
- Encoding may have been visual and semantic in Frost's study

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Multi-store model

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Components:
- Sensory Memory (SM)
- Short-term Memory (STM)
- Long-term Memory (LTM)
- Incoming sensory information
- Iconic Store
- Echoic Store
- Haptic Store
- Attention
- Maintenance rehearsal
- Information retrieval

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Sensory Memory

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Duration: Milliseconds
Capacity: Very large
Encoding: Auditory for hearing, visual for sight etc

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Short-term Memory

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Duration: Less than 18 seconds
Capacity: Limited, 7+-2 chunks
Encoding: Mainly acoustic

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Long-term Memory

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Duration: Potentially forever, in a healthy mind
Capacity: Very large
Encoding: Mainly semantic

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Process:
Attention

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- Information first arrives at SM
- Attention causes information to be transferred to STM

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Rehearsal

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- Information in STM is in a fragile state. It disappears through decay or displacement...
- It disappears if not rehearsed (decay)
- It disappears if new information enters (displacement)
- Verbal rehearsal maintains information in STM (information is repeated over and over again)
- Increasing verbal rehearsal leads to transfer fro m STM to LTM; the more rehearsal of an item, the better it is remembered = Maintenance rehearsal

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EVALUATION:
Multi-store model

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1) Research evidence supports the MSM
- Shows the existence of STM and LTM as separate stores
- Beardsley used brain scanning and found that the prefrontal cortex is active during STM but not LTM tasks
- Squire et al also used brain scanning and found that the hippo-campus is active when LTM is engaged
- Different areas of the brain in use supports separate stores

2) Case of HM supports MSM
- Hippocampi removed which led to an inability to transfer STM to LTM
- LTM not affected
- Shows that there is a distinction between short & long-term memories

3) Very simplified model
- STM can be further subdivided into verbal and visual, suggested by WMM
- LTM can be divided too (semantic, episodic, procedural) - Schachter et al
- MSM has single stores (LTM and STM)