Lecture 3 - STM

Question 1

Capacity of STM

Answer 1

7 +/- 2

Question 2

What is the digit span task?

Answer 2

• shows capacity of STM
• participants repeat back, in the correct order, a sequence of digits that have been read to them.
• shorter the sequence, the easier it is

Question 3

A way to increase the limited capacity of STM

Answer 3

Chunking - a way of recoding info.

-reduces the number of items that need to be stored in STM by increasing the info content of each unit

Question 4

What is the duration of STM, and why is it so short?

Answer 4

Duration: 20-30 seconds
Duration is so short because new info is constantly being forced into STM…
-either from the environment through the sensory register
-retrieval from long term memory

Question 5

How to prolong the duration of information in the STM

Answer 5

Rehearsal: repeating info over and over again…via we do this enough it will eventually enter our LTM

Question 6

What are the theories on why there is a loss of info from STM?

Answer 6

• Decay theory

- interference theory

Question 7

Decay theory

Answer 7

• suggests that forgetting due to the amount of time an item is held in STM
• when an item first enters STM it has a strong representation, that gradually weakens as time passes

Question 8

Evidence for decay theory

Answer 8

Brown-Peterson Task:

• a simple letter trigram (eg TDJ) is presented to a participant followed by a number such as 45.
• the participant is then asked to count down from the number out loud in threes until they’re told to stop.
• at this point, they’re asked to recall the trigram

Question 9

Results from the Brown-Peterson task

Answer 9

-mean performance degrades as length of time counting down increases.

Question 10

Probe digit task - Waugh and Norman

Answer 10

-found problems with the idea of decay theory.
-read a list of 16 digits to participants followed by a probe digit.
(the probe digit was one of the digits in the list of 16)
-the participants task was to say the target digit (the number that followed the probe digit)

Question 11

Results of the probe digit task

Answer 11

• half the participants were presented with stimuli at a rate of 4 digits a second, other half at a rate of one digit per second.
• results suggested that forgetting varied as a function of the location of the probe digit in the list.
• appears that later items interfere with earlier ones (if a probe digit was presented earlier in the list, there are more items left to interfere with the target digit)

Question 12

Interference theory

Answer 12

Suggests that we lose access to info stored in STM because other info interferes with it

Question 13

Further evidence for the interference theory - Keppel and Underwood

Answer 13

• found that performance on the Brown-Peterson task varied due to previously learnt trigrams interfering with subsequent trigrams
• this is known as PROACTIVE interference

Question 14

What is retroactive interference?

Answer 14

Where newly learnt info interferes with previously stored info

Question 15

Release from proactive interference - Wickens et al.

Answer 15

• changing the nature of the stimuli negates the effect of proactive interference.
• gave participants 3 trials of the Brown-Peterson task using trigrams.
• control group received a fourth trial of trigrams (letters)
• experimental group received a fourth trial of numbers
• performance of the control group continued to decline, whereas the experimental group returned to near perfect accuracy

Question 16

Release from proactive interference using semantic categories

Answer 16

-first three trial involved fruits (eg Apple-pear-orange)
-fourth trial stimuli were:
Fruits (control), vegetables (semantically similar), flowers (less so), professions (dissimilar)
-results demonstrated that the strength of the release from proactive interference varied due to the similarity of the semantic concepts

Question 17

STM retrieval - Serial recall task

Answer 17

• Participants presented with a list of items to learn

- then asked to repeat them back in the SAME order that they were presented (eg digit span task)

Question 18

STM retrieval - free recall task

Answer 18

• participant free to repeat back the items in any order

- easier than serial recall, as it requires less info to be processed

Question 19

Serial position effect

Answer 19

• primacy effect: easier to remember items at the start of a list. This is because they can be rehearsed longer, so they have a stronger memory trace.
• recency effect: easier to remember items late in a list. Due to there being fewer items that can interfere with these memory traces after they are encoded

Question 20

How can recency effects be nullified?

Answer 20

By getting participants to perform a different task before recalling the items (eg counting down from a number)
-this task interferes with the memory trace being held in STM

Question 21

Recognition - The Sternberg Task

Answer 21

• participants shown a set of letters, one at a time at a rate of one per second. This is called the MEMORY SET.
• following this, they are shown a PROBE item, which is another letter.
• participants have to indicate as quickly as possible whether the probe item was a member of the memory set.
• several hundred trials, memory sets ranging from 1-6 letters
• Sternberg was interested in the search process that participants used to scan through the items they had stored in their STM

Question 22

Sternberg Task - Serial self-terminating search

Answer 22

• probe item compare to each of the store memory set items one at a time until the question is answered.
• reaction times for YES answers tend to be shorter than those for NO answers.
• this is because if the probe item is in the memory set, the search can terminate as soon as it has been found.

Question 23

Sternberg Task - Parallel search

Answer 23

• each item in the memory compared to the probe item simultaneously
• reaction times will not vary, regardless of the response or the size of the memory set

Question 24

Sternberg Task - Serial Exhaustive Search

Answer 24

• memory set is searched in a serial fashion, but does not stop if it finds the answer, continues to search the rest of the memory set.
• yes and no answers would be the same
• however, reaction times would vary as a function of the memory set size.

Question 25

What search type in the Sternberg task best describes the data?

Answer 25

The serial exhaustive search

Question 26

STM and working memory

Answer 26

• STM seen as a passive store
• however some problems require active data processing
• this lead to the idea of Working memory