Coding, capacity and the duration of memory

short term memory

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

coding is mainly acoustic

capacity is between 5 and 9 items

duration is 18 seconds

long term memory

a permanent store where limitless amounts of information can be stored for long periods of time

coding is semantic (meaning)

unlimited capacity

can be stored for a lifetime

3 basic memory processes

coding, storage, retrieval

coding

the way in which

  information is represented in

  the memory store. E.g. sound, meaning or images

storage

where the information is kept. E.g. STM or LTM

retrieval

recalling a particular piece of information. E.g. a person’s name or how to spell ‘because’.

memory

The mental processes involved in registering, storing and retrieving information

capacity

The amount of information that can be held in a memory store

duration

The length of time information can be held in memory

types of coding

semantic, acoustic, visual

Miller (1956)

Aim: to investigate capacity of STM

Method: Literature review of published investigations into perceptions and STM, from the 1930s to 50s

Results: noted things come in 7s: notes on the musical scale, days in a week, deadly sins. Believed capacity was 7 ± 2 items

chunking - grouping sets of digits / letters to remember easier

Evaluation of Miller (1956)

• LIMITATION:

P: Unclear on STM capacity

E: He did not specify how large each ‘chunk’ was

C: so we are unable to conclude the exact size of the information ‘chunks’

• STRENGTH

P: Research support - Jacobs (1887)

E: Did a digit span test to examine STM capacity for numbers and letters. Used 443 female students (aged 8-19) who had to repeat a string of numbers or letters in the same order and the number of digits/letters was gradually increased until they could no longer recall the sequence.

C: Found students had an average span of 7.3 letters and 9.3 words, supporting Miller’s notion of 7 ± 2

Peterson and Peterson (1959)

Aim: To investigate how different short intervals containing an interference task affect the recall of items presented verbally, and to infer the duration of STM

Method: 24 male and female uni students. They were tested using 48 three-consonant nonsense syllables (trigrams) as well as cards containing three-digit numbers. The researcher spelled the syllable out then immediately said the three-digit number. The participant had to count backwards in 3s from that number to prevent repetition of the trigram. At the end of the pre-set interval between 3 and 18 seconds, a red light went on and the participant had to recall the trigram

Results: Longer interval meant less accurate recall

3 seconds = 80% correct recall

18 seconds = 10%

Conclusion: STM duration is 18 secs

Evaluation of Peterson and Peterson (1959)

• LIMITATION

P: Artificial stimulus

E: The study is not fully irrelevant because we sometimes try to remember fairly meaningless information (e.g. phone numbers). Even so, recalling consonant syllables is not a normal every day thing

C: Lacks external (ecological) validity

Bahrick (1975)

Aim: Investigate duration of LTM

Method: 392 participants aged 17 to 74 were given various tests such as:

• free recall test = asked to name all the people in their graduating class

• photo recognition test = participants were shown photos

Findings: subjects tested within 15 years of graduation were 90% accurate with identifying names and faces. After 48 years it declined to 80% for name recognition and 70% for photo recognition. Free recall test = after 15 years = 60% and after 48 years = 30%

Conclusion: you can remember certain types of information for almost a lifetime - supports semantic coding and lifetime duration of LTM

Evaluation of Bahrick (1975)

• STRENGTH

P: High external validity

E: Because the researchers investigated meaningful memories. When studies on LTM used meaningless pictures to be remembered, recall dropped

C: Suggests these findings reflect a more ‘real’ estimate of duration of LTM

• LIMITATION

P: Lacks population validity

E: Sample of 392 American uni graduates. Cannot generalise to other populations

C: Unable to conclude whether other populations would demonstrate the same ability to recall names and faces after 48 years

Baddeley (1966)

Aim: STM and LTM coding

Method: gave different lists of words to 4 groups of participants to remember:

1. acoustically similar (sounds the same)

2. acoustically dissimilar

3. semantically similar (means the same)

4. semantically dissimilar

they were shown the original words and asked to recall them in the correct order.

Findings: When they did this task immediately (STM) they did worse with acoustically similar words. When recalling after 20 mins (LTM) they did worse with semantically similar words

Conclusion: STM codes acoustically, LTM codes semantically

Evaluation of Baddeley (1966)

• STRENGTH

P: Identified a clear difference between the 2 memory stores

E: Later research showed there was some exceptions to Baddeley’s research but the conclusions were the same

C: Led to the MSM

• LIMITATION

P: Artificial stimuli

E: The words had no personal meaning

C: Findings have limited application