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 research

Researched coding

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

1. Acoustically similar words

2. Acoustically dissimilar words

3. Semantically similar

4. Semantically dissimilar

Asked to recall them in order. Immediately recalled from their STM. 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 research

Researched capacity of STM by measuring digit span

Researcher reads out 4 digits and the participant can recall them all correctly.

The researcher can then read out 5 digits and increase the number until the participant can’t recall them anymore.

Found that the mean span across all participants for digits was 9.3 and for letters was 7.3

Miller research

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 ± 2.

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

Peterson and Peterson research

Tested 24 students in 8 different trials.

On each trial the student was given a trigram or a nonsense syllable (XYG) to remember. Given a 3 digit number to count backwards from in 3s. Prevents any mental rehearsal. 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 3% could recall correctly.

Suggested that STM duration is about 18 seconds unless we repeat the information

Bahrick research

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

Tested recall in different ways:

1. Photo recognition test - some from the yearbook.

2. Free recall - Recalling all names from graduating class

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

After 48 years recall dropped to 70%

Wagenaar research

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

Identified a clear difference between 2 memory stores

Idea that STM is acoustic and LTM is semantic hasn’t been contested.

Important step in our understanding of memory. Led to the Multi Store Model.

W Baddeley

Artificial stimuli rather than meaningful material

Words had no personal meaning to the subjects.

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

Limited application for his findings.

S Jacobs

Replicated a lot of times.

Other studies with more controlled conditions confirmed his findings.

Suggests it is a valid test of digit span.

W Miller

Cowan

Overestimated STM capacity.

Reviewed other research and concluded that the capacity of STM is about 4 ± 1 chunks.

Suggests that the lower end of the estimate (5) is more appropriate than 7.

W Peterson + Peterson

Results may have been due to interference and not decay.

Interference from counting backwards could lead to the forgetting in STM.

Their conclusions are not valid.

S Bahrick

High external validity.

Investigated more meaningful memories.

When LTM studies were done using meaningless pictures, recall was lower.

Suggests that his findings are a more real estimate of LTM duration