PSY 368 Human
Memory
Short Term Memory
Announcements
• Quiz 2 today
• Exam 1 Feb. 15 (Wed)
• Experiment 1 Report. Due Feb. 15 (so start it early,
so that you can study for the exam)
Experiment 1 assignment
• Experiment 1 - Primacy and Recency Effects in Short-term
Memory (modified from Neath & Surprenant book pg. 61)
• Download from BB assignments page. Find 3 friends willing to participate
• Report (Due Wednesday Feb. 15): The results for all subjects will be reported in class.
Your assignment is to write a 2-3 page report that includes the following:
• brief description of the purpose and design of the experiment, including independent and
dependent variables
• brief description of the participants, materials, and procedure of the study, written in your own
words
• description of results and line graph of mean percentage recall by serial position
• discussion of conclusions that can be made from the results. Include answers to these questions:
•
How long does short-term memory appear to last?
•
How important is attention to retrieval from short-term memory?
•
What kinds of everyday tasks in life use short-term memory?
Structural Model
• Memory composed of storage structures that hold memories
for a period of time
• Sensory memory
• Short-term memory (STM) or Working memory
• Long-term memory (LTM)
Short-term Memory
• Brief History
• William James (1890) associated STM
with consciousness
• Also called “primary memory,”
“immediate memory,” or “working
memory”
• Modal models are prevalent in
descriptions of STM
• Focus on memory structure
Modal Models
• Broadbent (1958)
• Three systems (stores): S-system (sensory), P-system (STM), LTM
• Some sensory info (filtered) goes from S to P-system
• Assumed STM had limited capacity and info must be REHEARSED
to keep it from fading quickly
• Atkinson-Shiffrin Model (1968)
•
•
•
•
Sensory registers (by sense)
Short-term store (STM)
Long-term store (LTM)
Executive control processes regulate flow of info between stores
Short-term Memory
• Functions
• Re-codes info from sensory memory for longer storage
• Some info goes to long-term memory - stored for an
indefinite amount of time
• Rehearsal important part of STM
• Rehearsal maintains a memory trace for a short period of time
• Rehearsal helps transfer information from STM to LTM
• Features
• Capacity, Encoding, Duration, Retrieval
Short-term Memory
• Features
• Capacity, Encoding, Duration, Retrieval
STM Capacity
How much information can be held in STM?
• More limited capacity than Sensory memory
• Span = Measure of STM capacity
• Determined as 50% accurate ordered immediate
recall of short list (3-9 items)
• Visual or auditory information
STM Capacity
• Miller (1956) proposed capacity =
7 + or - 2 “chunks” of info
• Chunk = unit of info recoded from the
sensory input
• 1 chunk = 1 letter = 1 syllable = 1
word, etc.
STM Capacity
Finding your Span: Free recall
•I’ll read a list of items to you, when I’m done I’ll ask you
to recall as many of the items as you can (any order)
• Ready
• Ready
• Read list aloud
• Read list aloud
• Check list:
• Check list:
MPWSOYNCQALB
mop pie water sun olive yo-yo
nose car quiz actor lake banana
STM Capacity
• Span differs slightly depending on definition
of“chunk”(varies with “complexity” of the
chunk)
• Digit span = 7.7
• Word span = 5.5
Letter span = 6.35
Trigrams = 3.2
• But span can also vary based on chunking
abilities (integrated and elaborated with
knowledge in LTM)
STM Capacity
• Recoding can occur in STM if there is the time
and mental resources available to reorganize the
information
• Using long-term memory to recode information
– mnemonic devices
• Using a well learned strategy to recode information
• An example is verbally recoding information because
language usage is over learned
13
STM Capacity: Chunking
The capacity of the working memory may be
increased by “Chunking”
1776198514922004
1776198514922004
XCI AFB IVC RDN AIB MQZ
X CIA FBI VCR DNA IBM QZ
KCABLTCASIHET
CATBLACKISTHE
THE CAT IS BLACK
STM Capacity: Chunking
The capacity of the working memory may be
increased by “Chunking”
1776198514922004
1776198514922004
XCI AFB IVC RDN AIB MQZ
X CIA FBI VCR DNA IBM QZ
KCABLTCASIHET
CATBLACKISTHE
THE CAT IS BLACK
STM Capacity: Chunking
• Exceptional memory
• Chase & Ericsson (1981)
• Worked with S.F., who over 2 years (320 one hour training in a
lab practice sessions) increased digit span from 7 items to 79!
• S.F. member of track and cross-country teams, and would
relate digit strings to running times:
• e.g. for string 4 1 3 1...
• “I made four thirteen point one a mile time...”
• But also used other things
• Remembers 1943 as “near the end of World War II”
• But memory span for letters, words remained near 7
STM Capacity: Chunking
• Chase and Simon (1973a, 1973b)
• Used chess players
• Novices – <100 hours
• Experts – >10,000 hours
• Place pieces on the board (up to
24 of a middle game or random
middle game) and players
viewed for 5 seconds.
STM Capacity: Chunking
• Chase and Simon (1973a, 1973b)
• Information in memory is
stored as ‘chunks’
• A chunk is a familiar pattern
that can be used as a unit
• Masters have about 100,000
chunks
• Chunks can be recognized
instantly
• It takes about 10 seconds to
create a chunk
STM Capacity: Chunking
• Chase and Simon (1973a, 1973b)


Chunks are linked to
possible actions
In chess:
identification of
weaknesses, moves,
plans
f1
STM Capacity: Chunking
• Chase and Simon (1973a, 1973b)
Results:
• The chess master is
better at
reproducing actual
game positions.
• Master’s
performance drops
to level of beginner
when pieces are
arranged randomly.
STM Capacity
Brief Summary
• STM can hold about 7 ± 2 chunks of information
But see Cowan (2000): Reviews 6 current views against
this idea
1.
7 ± 2 is correct
the material
2.
Time is the limiting capacity not # of 6.
items
Separate capacity limits for storage and
processing
3.
No STM, all memory follows general 7.
rules (e.g., interference)
There are capacity limits that are task
specific
4.
No capacity limits, but constraints on
scheduling conflicts in performance
5.
Multiple capacity limits depending on
STM Capacity: Encoding
• What is the nature of the information encoded in
STM?
STM Capacity: Encoding
• Coding: the way information is represented
• Types of coding
• Auditory: acoustic, linguistic
• Semantic: meaning
• Visual: image
• Studies indicate that most info stored AUDITORILY
Conrad (1964)
• Presented letters briefly, were to write down the letters.
• Included letters that looked alike (V and X) or sounded alike (V and C)
• Analysis of errors indicated the tendency to confuse letters with
similar sounds – STM is auditory encoding
STM Capacity: Encoding
• Coding: the way information is represented
Baddeley (1966)
• In all lists, the words either sounded alike (cat, hat, cat) had similar
meanings (tiny, small, little) or were unrelated
• Results: more errors when subjects
studied lists of words that sounded
alike (man, mad, cap) than words
that have similar meanings (big,
huge, long)
• Conclusion: Similar sounding words confused in STM because memory
code was acoustic. Semantically similar words confused in LTM
because memory code was using meaning
STM Capacity: Encoding
• Coding: the way information is represented
Zhang & Simon (1985)
• Chinese radicals (no sound) and
characters (has sound) to Chinese native
speakers.
• Results –recalled 2.7 radicals (visual
code) versus 6.4 characters (auditory
code).
Visual coding in STM
• Coding: the way information is represented
Shepard & Metzler (1971)
• Subjects shown 2 objects and asked if
they were the same or different in
different orientations
• Results: Subjects took longer to
answer when the object had been
rotated further 600, 900, 1200
2200
2000
1800
• Interpretation: people held the
1st figure in STM and mentally
rotated the 2nd to make a
comparison
Same
Mirror
1600
1400
1200
0
26
45
90
135
STM Duration
How long does information last in STM?
STM Duration
• Duration of short term memory – Peterson & Peterson
(1959)/Brown (1958) procedure
• Experimenter says: CHJ 506
• Begin counting backwards by 3’s
• After a set time, recall three letters
• Subject says: 506, 503, 500…CHJ
• After three seconds of counting,
participants performed at 80%
• After 18 seconds of counting,
participants performed at 10%
STM Duration
• Decay or Interference (Displacement)?
• Could the counting backwards have actually interfered with
memory – not just preventing rehearsal
• Keppel and Underwood (1962)
• Reexamination of Brown and Peterson data
• Waugh and Norman (1965)
• Was the memory loss the result of the passage of time- more loss as
more time passed
• Or was increasing the amount of counting backwards interfering
with retention?
• Wickens’ work (1963, 1970, 1972, 1976)
• Release from proactive interference
29
STM Duration
Keppel & Underwood (1962)
•
•
Proposed P&P results because of the practice with trigrams in procedures.
When practice was eliminated the effects of delay in recall show little effect.
Short term memory, when rehearsal is prevented, is about 15-20 seconds.
Results
P&P result: A large drop in memory
for letters for a delay of 18 seconds
between presentation and test
Little decrease in performance on trial
1, and more decrease by trial 3.
• Conclusion: previous trials interfered with later trials – proactive interference
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
• After the last digit, you hear a tone...
31
TONE
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
• The tone is a signal to recall one of the digits. The last digit
before the tone (8) occurs only once at an earlier point in the list.
32
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• The subject’s task is to recall the digit following the probe.
• Between the digit, 4, and the tone, two things happen: (1) time
passes, and (2) more digits are presented.
33
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• Which is more important in causing forgetting, time or the more digits?
• The decay principle implies time; the interference implies digits.
34
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• Time and digits are correlated (confounded). To separate them, two rates
of presentation: slow (1 digit per second) and fast (4 digits per second).
35
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• If decay causes loss of information from short-term memory, the 16
second group should remember less because more time would have
passed before they responded
36
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• Made this comparison with the probe digit in each of the following
positions: 3 (shown here), 5, 7, 9, 10, 12, 13, or 14.
37
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• Results: Little to no (not significant) difference in recall with fast vs. slow
presentation with probes near the beginning of the list. Recall dropped
sharply as the probe was moved from the end toward the beginning.
38
STM Duration
Waugh and Norman (1965)
• Subjects verbally presented with lists of 16 digits at 2 presentation rates
• 1digit per second (takes 16 seconds to present list)
• 4 digits per second (takes 4 seconds to present)
• The last digit was the repeat of an earlier digit. Subjects asked to write
down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct
answer is 6
Probe
7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8
TONE
Recall
• Conclusion: As time passes, what mainly causes forgetting from shortterm memory is exposure to additional information, not the passage of
time.
39
STM Duration
Wickens, Born, & Allen (1963)
• Changing the nature of the items to be remembered
reverses the decline in performance due to proactive
interference- release from proactive interference
• Two groups of subjects given 3 trials following the BrownPeterson task (letters) - Memory performance declined with
each trial
• Control group given a 4th trial using letters
• Experimental group switched to remembering digits
STM Duration
Wickens, Born, & Allen (1963)
• Changing the nature of the items to be remembered
reverses the decline in performance due to proactive
interference- release from proactive interference
• Experimental group,
but not control group,
performed perfectly;
they were released
from proactive
interference
41
STM Duration
Wickens (1970, 1972, 1976)
• Proactive interference occurring as a result of semantic coding in STM
• 5 groups of subjects given 3 trials of lists of 3 words each all from the
same category where all list contained names of fruit
•
Group 1 – names of fruit
•
Group 2 – vegetable names
•
Group 3 – flower names
•
Group 4 - names of meats
•
Group 5 – names of different
professions
• Then all groups given a 4 trial where all list contained names of fruit
42
STM Duration
Wickens (1970, 1972, 1976)
• Results:
1st trial all
groups about
90% correct
2nd trial more
words in same
category
all groups about
50%
3rd trial words
still in same
category
all groups 35–
45 %
4th trial , shift to fruit
category
professions 80%, meat 50%,
flowers 47%, vegetables 40%
and fruit 32%
STM Duration
Wickens (1970, 1972, 1976)
• Results:
• Conclusion:
• Information was coded using semantic information causing groups
to confuse current list with previous lists
STM Retrieval
How do we get information out of STM?
• Retrieval from STM appears to operate by searching
STM contents one at a time (serial search)
• Sternberg (1966)
STM Retrieval
Sternberg (1966)
• study short list of 1 to 6 items followed by test probe - must
decide if probe item was in list, measured time to make Y/N
response
•
Two important variables were involved
• The number of letters in each list
• The location of the letter in the memory probe – in the beginning,
middle, or end
STM Retrieval
Sternberg (1966)
• Parallel processing
• Simultaneous handling
of multiple operations
• Response times should
be the same, regardless
of the size of the set of
items, because all
comparisons would be
done at once
• Serial processing
• Operations being done one after another
• It should take longer to retrieve four
digits than to retrieve two digits
• Exhaustive serial processing – the
participant always checks the test digit
against all digits in the set, even if a match
were found partway through the list
• Self-terminating serial processing – the
participant would check the test digit
against only those digits needed to make a
response
STM Retrieval
Sternberg (1966)
• Results
• Response times increased
linearly with set size but were
the same regardless of serial
position
• It indicates that serial
exhaustive model seems to be
right
• Conclusion: people search all items
• Subjects take longer to respond by
probe (by 40 ms) when an
additional item is added to the list •
• Same results for probes that were
in the list and probes that were not
in STM when asked to retrieve an item
(happens very fast)
Automatic process - fast and efficient,
done for every item – doesn’t stop once
a match is found
STM Retrieval
Serial Position Curve
• Primacy:
• better recall for items in
the beginning of the list
than those in the middle
• Recency:
• better recall for items at
the end of the list than
those in the middle
• due to retrieval from STM
STM Retrieval
Free recall Curve
• Primacy:
• better recall for items in
the beginning of the list
than those in the middle
• Recency:
• better recall for items at
the end of the list than
those in the middle
From Murdock (1962)
• due to retrieval from
STM
• Models of STM propose that
• Primacy is due to more rehearsal for items at beginning of list - LTM
• Recency due to immediate dumping of items from STM
STM Retrieval
Free recall Curve vs. serial recall curves
From Klien et al.
(2005)
• Primacy:
• better recall for items in
the beginning of the list
than those in the middle
• Recency:
• better recall for items at
the end of the list than
those in the middle
• due to retrieval from
STM
• Models of STM propose that
• Primacy is due to more rehearsal for items at beginning of list - LTM
• Recency due to immediate dumping of items from STM
• Recency is stronger effect than primacy in free recall
Problems with the Modal Models
• When distractor task is done after every list item
preventing items from staying in STM, recency effect
still occurs
• Primacy effects have also been shown to disappear
when rehearsal is prevented
STM Summary
• Duration:
• STM is short store of about 20 s without out
rehearsal
• Interference, rather than decay
• Capacity:
• Can hold 7 + or - 2 “chunks”(capacity)
• Chunking increases capacity of STM
• Encoding: Info mostly stored in auditory form
• Retrieval: Modal models suggest recency effects
mostly due to STM retrieval
More Recent Models
• Current models of STM focus more on
processing (than structures) and typically are
models of Working Memory that include STM
in some form