Coding, Capacity And Duration Of Memory

What is short-term memory (STM)?

The limited capacity memory store. In STM coding is mainly acoustic, capacity is between 5 and 9 items on average and duration is about 18 seconds.

What is meant by acoustic?

Through sound.

What is long-term memory (LTM)?

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

What is meant by semantic?

Through meaning.

What is coding?

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

What is capacity?

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

What is duration?

The length of time information can be held in memory.

Who conducted research on coding?

Baddley (1966).

What was Baddley’s procedure?

He gave different lists of words to four groups of participants to remember:

• Group 1 - acoustically similar.

• Group 2 - acoustically dissimilar.

• Group 3 - semantically similar.

• Group 4 - semantically dissimilar.

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

What did Baddley find?

When participants did the task immediately, recalling from STM, they tended to do worse with acoustically similar words.

When participants recalled words after a time interval of 20 minutes, recalling from LTM, they did worse with the semantically similar words.

What do the findings of Baddley suggest?

That information is coded acoustically in STM and semantically in LTM.

What is the strength of Baddley’s study?

It defined a clear difference between two memory stores, later research has shown some exceptions but the idea that coding is acoustic in STM and semantic in LTM has stood the test of time and was an important step in the understanding of the memory system, leading to the MSM.

What is the limitation of Baddley’s study?

It used quite artificial stimuli. For example, the the word lists had no personal meaning to the participants so therefore, Baddley’s findings may not tell us about coding in different situations, especially in everyday life. When processing more meaningful information, people may use semantic coding for STM.

What does articifical stimuli in Baddley’s study suggest?

That his findings have limited application.

Who conducted research on capacity?

• Jacobs (1887).

• Miller (1956).

How did Jacobs (1887) find out the capacity of STM?

By measuring digit span; e.g, the researcher reads ot four digits and the participant recalls these in the correct order. If this is correct, the researcher reads out five digits and so on until the participant can no longer recall the order corrrectly.

What did Jacobs find?

The mean span for digits across all participants was 9.3 and the mean span for letters was 7.3.

What is one strength of Jacob’s study?

It has been replicated and his findings have been confirmed by other, better controlled studies, suggesting that his study is a valid test of digit span in STM

What did Miller (1956) do?

He made observations of everyday practice, for example he noted that things come in sevens.

What did Miller think the span (capacity) of STM was?

About 7 items, plus or minus two.

What else did Miller note?

People can recall five words as easily as they can recall five letters, by chunking - grouping sets of digits or letters into units or chunks.

What is a limitation of Miller’s study?

He may have overestimated STM capacity - Cowan (2001) reviewed other research and concluded that the capacity of STM was only about 4 (plus or minus 1) chunks. This suggests that Miller;s lower estimate is more apppropriate than seven items.

Who conducted research on duration?

• Peterson and Peterson (1959).

• Bahrick et al. (1975).

What did Peterson and Peterson (1959) test?

24 students in eight trials each:

• On each trial the student was given a consonant syllable to remember, as well as a three digit number.

• The student counted backwards from this number until told to stop (preventing rehearsal).

• On each trial they were told to stop after varying amounts of time: 3, 6, 9, 12, 15 or 18.

What did Peterson and Peterson find?

• After 3 seconds, recall was about 80%.

• After 18 seconds, recall was about 3%.

What do the findings of Peterson and Peterson suggest?

That STM duration may be about 18 secons, unless we repeat the information over and over (rehearsal).

What is one limitation of Peterson and Peterson’s study?

The stimulus material was artificial; it is not completely irrelevant as we do sometimes try to remember fairly meaningless material but recalling consonant syllables does not reflect most everyday activites where what we are trying to remember is meaninngful.

What does meaningless stimuli mean for Peterson and Peterson’s study?

It lacked external validity.

What did Bahrick et al. (1975) study?

393 American participants aged between 17 and 74;

• Highschool yearbooks were obtained from the participants or directly from some school.

• Recall was tested either by a photo recognition test or by free recall.

What were the findings of Bahrick et al.?

• Partcipants tested within 15 years of graduation were about 90% accurate in photo recognition, free recall was 60%.

• After 48 years, recall declined to about 70% for photo recognition. Free recall was about 30%

What do the findings of Bahrick et al. show?

That LTM may last up to a lifetime for some material.

What is the strength of Bahrick et al’s study?

It has high external validity, as the researchers investigated meaningful memories. When studies on LTM used meaningless pictures, recall rates were lower (Shepard 1967).

What does the high external validity suggest about Bahrick et al.’s study?

That their findings reflect a more ‘real‘ estimate of the duration of LTM.