psy 368 human memory

PSY 368 Human MemoryShort 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)• Long-term memory (LTM)

or Working memory

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.

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

• Read list aloud

• Check list:

M P W S O Y N C Q A L B

• Ready

• Read list aloud

• Check list:

mop pie water sun olive yo-yo nose car quiz actor lake banana

STM Capacity

STM Capacity

• Span differs slightly depending on definition of“chunk”(varies with “complexity” of the chunk)• Digit span = 7.7 Letter span = 6.35• Word span = 5.5 Trigrams = 3.2

• But span can also vary based on chunking abilities (integrated and elaborated with knowledge in LTM)

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• 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

STM Capacity

STM Capacity: Chunking

The capacity of the working memory may be increased by “Chunking”

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K C A B L T C A S I H E T

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T H E C A T I S B L A C K

STM Capacity: Chunking

The capacity of the working memory may be increased by “Chunking”

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T H E C A T I S B L A C K

• 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

• 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.

• Chase and Simon (1973a, 1973b)

STM Capacity: Chunking

• 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

• Chase and Simon (1973a, 1973b)

STM Capacity: Chunking

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Chunks are linked to possible actions

In chess: identification of weaknesses, moves, plans

• Chase and Simon (1973a, 1973b)

STM Capacity: Chunking

Results: • The chess master

is better at reproducing actual game positions.

• Master’s performance drops to level of beginner when pieces are arranged randomly.

• Chase and Simon (1973a, 1973b)

STM Capacity: Chunking

Brief Summary

STM Capacity

• STM can hold about 7 ± 2 chunks of information

But see Cowan (2000): Reviews 6 current views against this idea

• 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

STM Capacity: Encoding

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

• Coding: the way information is represented

STM Capacity: Encoding

• 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

Baddeley (1966)• In all lists, the words either sounded alike (cat, hat, cat) had

similar meanings (tiny, small, little) or were unrelated

STM Capacity: Encoding

• Coding: the way information is represented

• 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).

Zhang & Simon (1985)

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Visual coding in STM

• Results: Subjects took longer to answer when the object had been rotated further 600, 900, 1200

• Interpretation: people held the 1st figure in STM and mentally rotated the 2nd to make a comparison

Shepard & Metzler (1971)

1200

1400

1600

1800

2000

2200

0 45 90 135

SameMirror

• Subjects shown 2 objects and asked if they were the same or different in different orientations

• Coding: the way information is represented

STM Duration

How long does information last in STM?

• 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• Duration of short term memory – Peterson & Peterson

(1959)/Brown (1958) procedure

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• 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

STM Duration

Keppel & Underwood (1962)

STM Duration

• 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.

• Conclusion: previous trials interfered with later trials – proactive interference

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.

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STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

• After the last digit, you hear a tone...

TONE

• 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

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• 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

STM Duration

Waugh and Norman (1965)

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.

Probe

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

• 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.

Recall

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

Recall

• Which is more important in causing forgetting, time or the more digits?• The decay principle implies time; the interference implies digits.

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

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).

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

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

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

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.

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

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.

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• 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

STM Duration

Waugh and Norman (1965)

7 0 8 4 1 6 0 9 5 5 3 7 2 4 7 8

TONE

Probe

Recall

• Conclusion: As time passes, what mainly causes forgetting from short-term memory is exposure to additional information, not the passage of time.

• Two groups of subjects given 3 trials following the Brown-Peterson task (letters) - Memory performance declined with each trial• Control group given a 4th trial using letters• Experimental group switched to remembering digits

Wickens, Born, & Allen (1963)

STM Duration

• Changing the nature of the items to be remembered reverses the decline in performance due to proactive interference- release from proactive interference

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• Experimental group, but not control group, performed perfectly; they were released from proactive interference

Wickens, Born, & Allen (1963)

STM Duration

• Changing the nature of the items to be remembered reverses the decline in performance due to proactive interference- release from proactive interference

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• 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

Wickens (1970, 1972, 1976)

• 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

STM Duration

Wickens (1970, 1972, 1976)

STM Duration

1st trial all

groups about 90% correct

• Results:

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%

Wickens (1970, 1972, 1976)

STM Duration

• 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

• 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

Sternberg (1966)

• 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

• 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

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

• 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

STM Retrieval

• Conclusion: people search all items 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

Sternberg (1966)

• 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

Serial Position Curve

STM Retrieval

STM Retrieval

• 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

Free recall Curve

From Murdock (1962)

• 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

• 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

Free recall Curve vs. serial recall curves

• 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

From Klien et al. (2005)

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