Coding, Capacity and Duration of STM and LTM

Definition of memory

the process in which information is encoded, stored and retrieved

What are the three types of memory

• sensory memory - information from environment, holds for fractions of seconds

• short - term memory - store where small amounts of memory can be stored for short amount of time (limited)

• long - term memory - permanent store where limitless amount of info can be stores for long period of time

definition of encoding

changing information so that it can be stored

definition of retrieval

recovering information from storage

definition of capacity

how much info can be stored

definition of duration

length of time info can be stored in memory

EXPERIMENT - CAPACITY ON STM (JACOBS 1887)

• Aim - research capacity on STM

• Procedure - had to repeat back the strings of letters or digits the psychologist said. Kept increasing the length until unable to recall the list accurately.

• The digit span was the longest sequence recalled correctly by 50% of participants.

• Findings - average recalled 9 digits and 7 letters. mean span for digits 9.3 and mean span for letters was 7.3.

• Conclusion - has limited store capacity of 5 to 9 items - use diff memory techniques could increase capacity.

Miller - conducted similar study, found the magic number 7+ or - 2 items can be remembered, you can remember more through chunking

EVALUATION OF CAPACITY STM EXPERIMENT

• Negative - done long time ago before importance of controlling experiments was understood. Could have been unreliable as a lack of control over extraneous variable.

• Positive - High reliability - similar procedures done found similar results e.g. Miller (7 +/ 2 items) and is easy replicable

• Negative - there is variability in population so theory doesn’t apply to everyone, some naturally better at remembering

• Strength - can apply in real life scenarios e.g. license plates and chunking phone numbers

Is there an experiment on the capacity of LTM?

No

• impossible to test

• difficult as you cannot test duration

Summary of capacity

• sensory memory - vast

• short term memory - limited

• long term memory - unlimited

EXPERIMENT OF DURATION OF STM (PETERSON & PETERSON)

• Aim - if rehearsal is necessary to hold info in STM store

• Procedure - given 3 sets of letter to remember, immediately asked to recall backwards in 3s out loud. (prevents rehearsal) and had to recall letters in correct order

• Findings - 3 seconds average recall a 90%. 18 seconds average recall at 3%. virtually forgot information after 18 seconds.

• Conclusion - cannot hold information unless rehearsed. Has a limited duration of up to 18-30 seconds.

EVALUATION OF EXPERIMENT ON DURATION OF STM (PETERSON & PETERSON)

• Negative - lacks ecological validity - unrealistic in everyday life as not asked to learn trigrams

• Positive - controlled experiment - can be replicated and reduces bias.

• Negative - lacks mundane realism and can cause demand characteristics

• lacks cross-cultural and population validity - only on American university students - may not be representative of other cultures, age group - limits generalisation

meaning of displacement

new information displaces older information and pushes it out of STM

EXPERIMENT FOR DURATION IN LTM (BAHRICK)

• Aim - to test duration in long term memory

• Procedure - 392 American participants between 17 and 74. Photo recognition from grad year book and recall test of their class.

• Findings - within 15 years of graduation - 90% accurate and after 48 years - decline to 70%. free recall (without any cues - photos) within 15 years - 60% accurate and after 48 years - dropped to 30%.

EVALUATION FOR DURATION LTM EXPERIMENT (BAHRICK)

• Positive - high ecological validity - used real life memories - more realistic and generalisable to every day memory

• Negative - lack of control over extraneous variables - could have looked at yearbooks recently or stayed in contact with classmate (boosts there memory)

• High population validity - range of ages - can conclude about LTM over a lifespan

• Limits cross - cultural validity - only Americans and not other cultures - reduces external validity - may have different social practices and emphasis on education/memory

What are the three ways of encoding information

• acoustic - sound of the stimulus

• visual - physical appearance of stimulus

• semantic - meaning of stimulus

EXPERIMENT INTO ENCODING FOR LTM AND STM (BADDELEY)

• Aim - find out how we encode information

• Procedure - Participants shown a list of words in 4 categories - Acoustically similar/dissimilar and semantically similar/dissimilar

• LTM - asked to recall words after 20 min delay

• STM - asked to recall after a distraction task

• STM made more errors in acoustically similar and LTM made more errors in semantically similar

• Conclusion - STM encodes acoustically and LTM encodes semantically

EVALUATION OF EXPERIMENT INTO ENCODING STM & LTM (BADDELEY)

• positive - controlled environment - high external validity - can be replicated and tested for reliabilities and low extraneous variables

• Negative - individual difference - limits population validity as only university students asked - not representative of wider population

• lacks ecological validity - doesn’t reflect daily memory use - encode more meaningful complex info so cannot generalise

SENSORY MEMORY

• duration - less than a second

• capacity - vast

• encoding - iconic and echoic

SHORT TERM MEMORY

• Duration - 18 seconds

• Capacity - limited

• Encoding - Acoustic

LONG TERM MEMORY

• Duration - unlimited

• Capacity - unlimited

• Encoding - Semantic