Coding, capacity and duration of memory

Capacity

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

Chunking

Grouping sets of digits or letters into chunks

Coding

The format in which information is stored in the various memory stores

Duration

The length of time information can be held in memory.

Long-term memory

The permanent memory store. In LTM coding is mainly semantic (meaning), has unlimited capacity and can store memories for up to a lifetime

Short-term memory

The limited-capacity memory store. In STM coding is mainly acoustic (sounds), capacity is between 5 and 9 items and duration is about 18 seconds

Baddeley 1966

Researched coding

Gave different lists of words to 4 groups of participants to remember:

1. Acoustically similar words (sound similar)

2. Acoustically dissimilar words (sound different)

3. Semantically similar (similar meaning)

4. Semantically dissimilar (different meanings)

Participants were shown these words and were asked to recall them in order. They started by recalling immediately from their STM and did worse with acoustically similar words. After 20 minutes they recalled from their LTM and did worse with semantically similar words.

Suggests that information is coded acoustically in STM and semantically in LTM.

Jacobs 1887

Wanted to find out how much information could STM hold at a time.

Researched digit span of coding

For example a researcher reads out 4 digits and the participant can recall them all correctly.

If this is correct the researcher can read out 5 digits and increase the number until the participant can’t recall them anymore.

This is the individual’s digit span.

He found that the mean span across all participants for digits was 9.3. The mean span for letters was 7.3

Miller 1956

Made observations for everyday practice.

He noted that everything comes in 7s (7 days a week, 7 notes in a scale)

He thought this wasn’t an accident and suggested that the capacity of STM might be about 7 plus or minus 2.

Also noted that people can recall 5 words as easily as they can recall 5 letters. Doing this by chunking

Peterson and Peterson 1959

Tested 24 students in 8 different trials.

On each trial the student was given a trigram or a nonsense syllable (XYG) to remember. They also were given a 3 digit number to count backwards from. Prevents any mental rehearsal.

They were told to stop after varying periods of time, 3, 6, 9,12, 15, 18 seconds.

After 3 seconds 80% could recall it correctly. After 18 seconds only 3% could recall correctly.

They suggested that STM duration may be about 18 seconds unless we repeat the information over and over.

Bahrick 1975

Studied 392 American participants aged between 17 and 74. High school yearbooks were obtained from the participants or directly from their schools.

They tested recall in different ways:

1. Photo recognition test (50 photos) some from the yearbook.

2. Free recall where participants recalled all names of their graduating class.

Participants tested within 15 years of graduation were accurate 90% of the time.

After 48 years recall dropped to 70%

Wagenaar study

Recorded 2400 events over 6 years in a diary and tried to recall them

Very accurate recall, supports the fact that the capicity is extremely large.

S Baddeley

His study on encoding identified 2 different memory stores. Led to the MSM of memory.

STM Acoustic. LTM Semantic.

W Baddeley

Words had no personal meaning to the subjects.

There may be semantic encoding in STM for more meaningful pieces of information.

Limited application.

S Jacobs

Replicated a lot of times.

These confirmed his findings.

Valid test of digit span.

W Miller

Overestimated STM capacity.

Capacity of 5 better than of 7.

W Peterson + Peterson

The study could’ve been done on interference and not decay.

Counting backwards takes up more processing.

Their conclusions are not valid.

S Bahrick

High external validity.

More meaningful memories so his estimate for LTM duration is more real.