Lecture 3 - STM Flashcards
Capacity of STM
7 +/- 2
What is the digit span task?
- 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
A way to increase the limited capacity of STM
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
What is the duration of STM, and why is it so short?
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
How to prolong the duration of information in the STM
Rehearsal: repeating info over and over again…via we do this enough it will eventually enter our LTM
What are the theories on why there is a loss of info from STM?
- Decay theory
- interference theory
Decay theory
- 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
Evidence for decay theory
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
Results from the Brown-Peterson task
-mean performance degrades as length of time counting down increases.
Probe digit task - Waugh and Norman
-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)
Results of the probe digit task
- 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)
Interference theory
Suggests that we lose access to info stored in STM because other info interferes with it
Further evidence for the interference theory - Keppel and Underwood
- found that performance on the Brown-Peterson task varied due to previously learnt trigrams interfering with subsequent trigrams
- this is known as PROACTIVE interference
What is retroactive interference?
Where newly learnt info interferes with previously stored info
Release from proactive interference - Wickens et al.
- 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
Release from proactive interference using semantic categories
-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
STM retrieval - Serial recall task
- 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)
STM retrieval - free recall task
- participant free to repeat back the items in any order
- easier than serial recall, as it requires less info to be processed
Serial position effect
- 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
How can recency effects be nullified?
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
Recognition - The Sternberg Task
- 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
Sternberg Task - Serial self-terminating search
- 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.
Sternberg Task - Parallel search
- 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
Sternberg Task - Serial Exhaustive Search
- 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.
