Cognitive Flashcards
Capacity of STM - Millers Magic 7 (1956)
Capacity of STM - limited
Miller noticed in everyday practice that things come in sevens such as notes on a musical scale, days of the week, the deadly sins etc
He concluded that the capacity of the STM was about 7 items (plus or minus 2) and this could be increased by chunking - groups sets of digits/letters together into meaningful units
Capacity of STM - Jacob’s (1887) digit span test
Researcher reads 4 digits and increases by one each time until the ptp cannot correctly recall all of them. The final number of digits correctly recalled is their digit span.
On average ptps could recall 9.3 numbers and 7.3 letters in the correct order immediately after they were presented.
Strength of Jacob’s study - replicable
It’s an old study so may have lacked adequate controls such as confounding variables eg ptps being distracted. Despite this Jacob’s findings have been confirmed in later controlled studies eg Boop and Verhaeghen 2005) shows Jacob’s study is a valid measure of STM digits span.
Weakness of miler magic 7 - overestimates STM capacity
Jacob’s research does support millers however Cowan (2001) reviewed other research and concluded that the capacity of STM was only about 4 (plus or minus 1) chunks. This suggests that the lower end of Millers estimate (5 items) is more appropriate than 7 items.
Capacity of LTM
Potentially unlimited
Duration of STM
Limited duration - seconds. Info can be kept in for longer through rehearsal
Duration of STM - Peterson and Peterson (1959) Trigrams
24 psych students were given trigrams to recall and a 3 digit number to count backwards from in 3s or 4s to prevent rehearsal. The retention interval was varied - 3,6,9,12,15 or 18 seconds.
After 3 seconds the average recall was around 80% and after 18 seconds it was 3%. STM duration without rehearsal is up to 18 seconds.
Weakness of Peterson and Peterson study - uses meaningless stimuli
The recall of trigrams does not reflect meaningful everyday memory tasks so therefore the study lacks external validity.
Duration of LTM - Bahrick et al (1975) Yearbook photos
Ptps were 392 Americans aged between 17 and 74
1 - recognition test - 50 photos from high school yearbook
2 - free recall test - ptps listed names from their graduating class
Findings - recognition test - 90% accurate after 15yrs and 70% accurate after 48yrs
Free recall test - 60% accurate after 15yrs and 30% accurate after 48yrs
Free recall ability decreases with age to a large extent
Strength of Bahrick et al (1975) study - high external validity
Uses everyday meaningful memories eg peoples faces and names . When lab studies done with meaningless pictures to be remembered recall rates were lower - Stephenson 1967. Means that Bahrick et als findings reflect a more ‘real’ estimate of duration of LTM.
Coding in STM
Acoustically
Info is stored in memory in different forms depending on the memory store. The process of converting information between different forms is called coding.
Coding in LTM
Semantically
Coding in STM and LTM - Baddely (1966) acoustic and semantic
Gave different lists of words to four different groups of people
- acoustically similar (eg cat, cab, can) or dissimilar (eg pit, few, cow)
- semantically similar (eg great, large, huge) or dissimilar (eg good, huge, hot)
Immediate recall worse with acoustically similar words. STM is acoustic
After 20 mins worse with semantically similar words. LTM is semantic
Strength of Baddeleys study - used controlled conditions
Study had controls in place to prevent extraneous variables from confounding the results eg poor hearing - hearing test and only used people worth perfect scores. The experiment took place in controlled conditions in lab.
Limitation of Baddeleys study - used artificial stimuli
Words used had no personal meaning to ptps so tells us little about coding for everyday memory tasks. When processing more meaningful information people use semantic coding even for STM. Means the findings of this study have limited application.
MSM - Atkinson and Shiffre (1968)
The MSM describes how information flows through the memory system. Memory is made of three unitary stores that vary in encoding, duration and capacity.
MSM - Sensory register
All stimuli from the environment passes into the sensory register. It 5 memory stores one for each sense eg echoic - codes acoustically and iconic - is visual.
Coding - modality - specific, depends on the sense (visual in iconic, acoustic in echoic etc)
Duration - very brief, less than half a second
Capacity - very high
The sensory register holds an image for a few seconds while it is scanned to decide if attention should be paid and passed on through the system for further processing
MSM - transfer from SR to STM
Info passes further into memory only if attention is paid to it (attention is the key process)
MSM - STM
A limited capacity store of Temporay duration
- coding - acoustic
- duration - about 18 seconds unless info rehearsed
- capacity - between 5 and 9 (7 plus or minus 2) items before some forgetting occurs
MSM - transfer from STM to LTM
Maintenance rehearsal occurs when we repeat material to ourselves. We can keep info in STM as long as we rehearse it. If we rehearse it long enough it goes into LTM.
MSM - LTM
A permanent memory store
- coding - mostly semantic
- duration - potentially up to a lifetime
- capacity - potentially unlimited
MSM - retrieval from LTM
When we want to recall info from LTM it has to be transferred back to the STM by a process called retrieval
Limitation of MSM - evidence suggesting there is more than one store
Shallice and Warrington 1970 studied KF who suffered brain injuries after a motorcycle accident. His STM recall for digits was poor when he heard them but much better when he read them. He had trouble with verbal STM not visual STM. Other studies confirm there may be seperate STM stores for non-verbal sounds eg noises. So MSM is wrong to claim there is only one store of STM processing different types of information.
Support - Glanzer and Cunitz 1966 primary and recency effect
Words are better recalled from beginning - primary effect and end of a list - recency effect. In the primary effect words go to LTM. In recency effect - words are in STM and start of recall. Support for separate STM and LTM stores