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Samenvatting leren en geheugen deeltentamen 2
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Hoorcollege 11: the neural basis of visual sensory memoryYou immediately and automatically create an iconic memory
• Single, visible, precategorical, high capacity, quickly-decaying memory that holds incoming visual
stimulation for further processing.
Memory is not 1 thing
• Sensory information coming in → sensory buffer (visual persistence) → encoding into short-term
memory → working memory (basis for most of your actions)
Visual sensory memory is not 1 thing either
• There has been a lot of discussion about visual sensory memory
• How the brain enables iconic memory is not known yet
• We have to distinguish between ‘visible persistence’, ‘visual analog’, ‘postcategorical information
• We can call these concepts retinal afterimages, iconic memory (low-level icon), and fragile memory
(high-level icon)
A big question
• Memory is often used to measure consciousness, everything that exists in first person existence
o Perceptual and cognitive parts
• Cognitive blindness: eyes work perfectly, but they cannot ‘see’ anything
Same neural mechanisms that underly memory also underly awareness.
Working memory → working consciousness
Ancient history on visual short-term memory
Aristotle → “Memory is, therefore, neither Perception nor Conception, but a state or affection of one of
these, conditioned by a lapse of time.”
Visible persistence
Visible persistence does not require an intense blast of light in order to be generated, it is brief in duration,
and it has the same contrast polarity as the originating stimulus (i.e., it is not a negative afterimage).
Storage model of visible persistence
• Sensory store → some of it gets passed on to the relevant areas. Visual persistence is a
continuation of all of the sensory information coming in
• Retinal cells are still active even though the image is gone.
How can we measure the duration of visible persistence
Vary the ISI → when
they can see where the missing dot is, then there is visible
persistence
Short ISI → the visible persistence overlap. → overlapping
image
Long ISI → no overlapping, so no overlapping image
Up to 80 ms, the visual persistence is really there, after
that there is a big drop
Visible persistence is linked to a burst of neural activity time-locked to stimulus onset
,To some extend you can say that if a stimulus is presented for longer,
then the retinal cells already become exhausted while the stimulus is
still there. After the stimulus is removed, they have less energy to still
fire. → reverse-duration effect
• The longer you present a stimulus the less overlap there will be
Briefly → the relaxation of these cells coincide the duration of the visual
after effect
Past critical period → you can no longer integrate into one percept.
Visible persistence in short:
• Positive afterimage
• Duration of afterimage is linked to stimulus onset (long-lasting afterimage for brief stimulus, brief
afterimage for long-lasting stimulus)
• Related to rods in the eye (we’ll come back to this)
• Will last longer when people are dark adapted
• Lots of different paradigms (see Article)
Iconic memory: important concepts
• Capacity: 9+ Sperling, 20+ Averbach/Sligte
• Time course (lifetime): ±0.5 seconds (Sperling), 4 seconds (Sligte)
• Masking: Low-level features (Sperling), high-level objects (Sligte)
• Attention: the task itself is difficult
• Representational format: precategorical/features vs. postcategorical/objects.
It seems you don’t need attention for iconic memory
Experiment van Sperling
Whole report: report as much as you can
Partial report: only report from the row that is qued
Findings:
• Partial report superiority effect
• Up to ½ a second you are better at partial
report
• Whole report condition → while you’re
reporting, you are forgetting what you saw
Visual working memory
• Say whether there is a difference in the two arrays
• Capacity is basically never higher than 4
• Delay doesn’t matter
• If you get new visual information, it erases the previously stored iconic memory
• Similarity cause the iconic memory to be erased
From set size 4, your percentage correct does not increase. You can only store 4 items in you working
memory
Working memory activates a widespread network of brain regions
• Inattentional blindness → scene that goes on for a long time. For you to detect the changes is for
you to rely on your visual working memory. This is very difficult because you have only limited
access there. You only remember very little in a scene where things are very similar.
• Early sensory areas and later on in frontal areas.
, • Disturbing these areas → study what role these areas play → TMS
The combined VSTM paradigm: time for trouble
Partial-report change detection task
• Adapt change detection task → allows people to tap into their sensory memory, and suddenly you
have a very rich visual memory. Access their memory before the second scene, so before the test
display. The second scene erases the first array. If there is a change, it happens as this location.
Access iconic memory → Capacity will be very high.
• Compare: shorter retention interval & exact same time from memory display offset , when memory
display disappears, until the cue and the test display together are shown.
Experiment:
• Black and white display → strong after image → rods very sensitive to luminance, but they are color
blind. They cause this visual persistence. Rods keep on firing
• Isoluminant display → weak after image
• Most left panel → capacity is limitless. Only with a black and white display.
• Eliminate visual persistence → still have a capacity of almost 16
• A reflection of what people actually experience
• Big difference in the black/white and isoluminant displays → iconic memory condition → part of the
effect is explained by an after image.
• Working memory has a smaller capacity than fragile memory
o It’s not timing
o After 1 second you know which orientation you have to remember
o Only difference is, fragile: you only have the cue. Working memory: test array is shown
together with the cue. → interference
• Sensory memory is stored in the same areas as where you perceive/ consciously experience visual
stimuli. What happens in the occipital parts, you store and perceive visual information →
interference. Visual information is erased when similar visual stimuli are perceived.
Difference between FM & WM is → if you get visual interference or not
, Explain these observations → where in the visual hierarchy?
• After image → retina
• Fragile VSTM → not until V4 otherwise perceptive fields would be too big
• WM → parietal frontal areas
Natural consequences of the visual architecture:
• Higher up in visual hierarchy:
o Larger receptive fields*1
o More complex tuning*1
o Longer lifetime of neural responses*2
• Consequences (as we go up):
o Increasingly strict capacity limits
o Loss of visual details/more abstract representations
o Representational lifetime gets longer
• Low-pass filter: limiting capacity, increasing lifetime/robustness
>> VSTM capacity should decrease when moving up the visual hierarchy
>> VSTM lifetime should increase when moving up the visual hierarchy
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