short term memory.ppt - donald bren school of information...
TRANSCRIPT
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VISUAL MEMORY
Visual Perception
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Slide 2 Aditi Majumder, UCI
Memory is unqiue
Other aspects of visual perception Bombard us with stimuli at every instance
Memory Helps us to make sense from chain of such
instances
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Slide 3 Aditi Majumder, UCI
Two Theories in 1800s
Herman Ebbinghaus Undifferentiated memory system One memory overwritten only with “new” memories
William James Primary memory: 10s of seconds Secondary memory: Years
1960s experiments confirmed Short term memory (STM) Long term memory (LTM) Iconic memory (very small memory buffer)
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Slide 4 Aditi Majumder, UCI
Classify based on
Duration Amount of time it lasts
Content Kind of information stored
Loss Ways of loss of information Autonomous decay vs conflicting new memories
Capacity Maintenance
Methods to refresh
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Slide 5 Aditi Majumder, UCI
Discovery to Iconic Memory
Early experiments (1880s) studied the spanof apprehension
Number of letters a person could perceive in a single, very brief visual presentation DEMO!
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Slide 6 Aditi Majumder, UCI
Demo
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Slide 7 Aditi Majumder, UCI
Span of Apprehension
How many letters can you report?
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Slide 8 Aditi Majumder, UCI
Whole Report Performance
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Slide 9 Aditi Majumder, UCI
Discovery of Iconic Memory
In 1950 George Sperling duplicated results Did not match visual experience Reporting is taking too long Cannot report all that is retained within the time
provided Changed the reporting Cue based reporting on a fraction of letters
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Slide 10 Aditi Majumder, UCI
Audio cue (after letter display)
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Slide 11 Aditi Majumder, UCI
Location Cue
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Slide 12 Aditi Majumder, UCI
Location Cue
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Slide 13 Aditi Majumder, UCI
Location Cue
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Slide 14 Aditi Majumder, UCI
Location Cue
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Slide 15 Aditi Majumder, UCI
Location Cue
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Slide 16 Aditi Majumder, UCI
Location Cue
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Slide 17 Aditi Majumder, UCI
Partial Report Performance
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Slide 18 Aditi Majumder, UCI
Duration of Iconic Memory
Delay between display and cuing
If delay is long enough, partial report will be similar as whole report plot
Effect of context Mostly light Iconic memory duration: ½ sec
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Slide 19 Aditi Majumder, UCI
Content of Iconic Memory
Effectiveness of different cues Spatial position
Tone cuing for color, letter/number, row etc Effective cues Position, Color, Shape, Size
Category is ineffective Pre-categorical
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Slide 20 Aditi Majumder, UCI
Maintenance and Loss
Cannot be maintained voluntarily Loss By autonomous decay By interference
Called masking Discovered by accident
Cuing by a circle Completely erased signal Metacontrast masking or erasure
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Slide 21 Aditi Majumder, UCI
Masking Terminology
Forward or Backward Masks Homogeneous vs Noise vs Patterned Simultaneous Onset Asynchrony (SOA)
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Slide 22 Aditi Majumder, UCI
Integration Masking
Flat color mask Double the intensity of the target
No target identification for 0-16ms Improves as SOA increases Complete identification at 200ms
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Slide 23 Aditi Majumder, UCI
Interruption Masking
Brightness of mask halved instead of doubled No masking at 0ms Masking maximizes at 50ms Then improves
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Slide 24 Aditi Majumder, UCI
Metacontrast Masking (interruption)
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Slide 25 Aditi Majumder, UCI
Metacontrast Masking (interruption)
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Slide 26 Aditi Majumder, UCI
What was the letter?
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Slide 27 Aditi Majumder, UCI
Circle sometimes erased the letter Masking circle with a bigger circle undoes the
effect!!
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Slide 28 Aditi Majumder, UCI
Interocular Masking
Dual mechanisms Homogeneous masks only degrade performance
is presented to the same eye as the target Processing occurs prior to V1 area of cortex
Patterned masks degrade performance irrespective of which eye they are presented to Processing occurs after V1 area of cortex
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Slide 29 Aditi Majumder, UCI
Persistance
Does it work by persistence? You can report since you can still see
Measured by a clever method Set a tone along with start of stimulus Have user stop the tone when he no longer sees it This time is found to be longer than stimulus Subtract stimulus time to find persistance Increasing brightness or duration reduced
persistance
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Slide 30 Aditi Majumder, UCI
What is the use of iconic memory?
Processing during saccadic movements? During motion processing? By-product of some other mechanism?
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Slide 31 Aditi Majumder, UCI
Visual Short Term Memory (STM)
Gap between iconic and long term memory Iconic memory is for less than 1 sec Even meaningful conversations cannot be
explained by either iconic or long term memory How to measure? Present meaningful stimulus and ask after 1 sec But subjects will categorize
Was it knowledge or STM Need stimulus that cannot be categorized
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Slide 32 Aditi Majumder, UCI
Meaningless patterns
William Philips in1975 Show meaningless grid
of random squares Test for retention after 0-
9 seconds Same/different answer
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Slide 33 Aditi Majumder, UCI
Proof of STM
• Near perfect memory for less than 1 sec• Iconic memory
• Performance goes down dramatically after that• Well above chance
(50%)• For smaller grids
• This is proof for existance of STM
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Slide 34 Aditi Majumder, UCI
Further proof of STM
Iconic memory is spatially dependent
If second stimulus shifted in position, iconic memory fails
STM recall increases in performance
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Slide 35 Aditi Majumder, UCI
STM or LTM
Learning from verbal experiments Present a list of words Free recall Serial position curve
First and last set of words are better recalled Recency effect: Higher recall of last set of words Delay recall by a distracting task removes recency
effect Recency effect is due to STM Slowing presentation increases recall from LTM
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Slide 36 Aditi Majumder, UCI
STM vs LTM
Same experiment repeated with grid patterns Forced choice rather than
recall Recency effect for last grid
Eliminated by a coginitively demanding distractor
Faster rates reduces performance Recency effect persists
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Slide 37 Aditi Majumder, UCI
STM properties
Duration:10 seconds, longer if no interference Content: Object based spatial coordinates, Post-
categorical Capacity: Single item Loss: Mainly through replacement, though
maybe decay if no rehearsal Maintenance: Can be rehearsed
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Slide 38 Aditi Majumder, UCI
Transaccadic Memory
Conjecture: Fusion of visual stimuli during saccade
Experiment Two displays Locate the missing dot With and without saccade
Iconic vs transaccadic memory Failure with saccade
No evidence of fusion
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Slide 39 Aditi Majumder, UCI
Same as STM
STM is acting rather than iconic memory Limited to 4 items: Capacity Almost no decay within a second: Duration Better for identification than location
How do we perceive stable world during saccade? Not due to fusion If target is unmoved, other changes go unnoticed
during saccade
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Slide 40 Aditi Majumder, UCI
Conceptual Organization
Meaningless visual materials To reduce interference conceptual categorization How to study conceptual categorization? How long does it take?
Rapid Series Visual Presentation (RSVP) Series of pics presented for 1-1000s Each picture presented for 100ms-2s Detection (e.g. did you see a picnic scene?) Recognition (e.g. What did the picnic scene show?)
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Slide 41 Aditi Majumder, UCI
Results of RSVP
Fast presentation rate (100ms), detection is possible, but no recognition
Cannot comprehend pictures shown for 100-200ms
However, standalone pictures shown for same duration with noise mask can be both detected and recognized
Meaningful image within 500ms has a masking effect
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Slide 42 Aditi Majumder, UCI
Conceptual Short Term Memory
Takes 100-200ms to log in CSTM Takes another 400ms to process for
recognition If interrupted at that time, the image is lost