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Memory
Memory
Memory is the capacity to retain information over
time (in both living organisms and computers).
There is no single memory system in our brain but
several, functionally distinct systems.
They differ in
• the type of information that they store,
• the duration for which it is stored, and
• the maximum amount of information that can
be stored (capacity).
The psychology of memory: two pioneers...
William James
Hermann Ebbinghaus
History of the STS/LTS distinction
1890 - William James draws distinction between primary and
secondary memory.
PRIMARY MEMORY
SECONDARY MEMORY
Reward portion of present
space of time
Linked to conscious experience
Genuine past
Unconscious - permanent
Retrieval is effortless
Retrieval is effortful
The development of computers in the 1960s provided another
analogy which split memory into two:
CPU/RAM = STS, STORAGE = LTS
Modal model of memory developed by Atkinson & Shiffrin (1968)
The modal model of memory
Sensory
Rehearsal
Store
Sensory
Store
Short
Long
Term
Term
Store
Store
Transfer
Sensory
Store
Displacement
(Forgetting)
But what is the evidence for separate STS / LTS?
The Modal Model (Atkinson & Shiffrin)
STIMULUS INPUT
e.g. Visual (iconic)
Auditory (echoic), etc.
Some Control Processes:
Rehearsal, Coding,
Decisions, Retrieval
Strategies
Sensory
Memory
RESPONSE
OUTPUT
Short-term
Memory
RETRIEVAL
ENCODING
Long-term
Memory
Sensory Memory
Sensory memory is a “short-term storage facility” for
incoming sensory information.
Holds information only long enough for higher-level
cognitive processes to operate on it, e.g., object
recognition.
There is one separate form of sensory memory for
each of the five senses, for example:
• Iconic memory: visual sensory memory holding a
“snapshot” of recent (200-300 ms) visual input.
• Echoic memory: auditory sensory memory
“echoing” recent (several seconds) auditory input.
Iconic Memory Experiment
Sperling (1963):
43 array of randomly chosen English letters
• Whole-report condition:
• After brief presentation, letters disappear
• Subjects have to report which letters were shown
• Partial-report condition:
• After brief presentation, letters disappear
• The pitch of a played tone indicates whether to
report the letters in the first, second, or third row.
Iconic Memory Experiment
Whole-Report Condition
Your task: Memorize as many letters as
possible in the following display and report
them after the display has disappeared.
Iconic Memory Experiment
Iconic Memory Experiment
HBXV
MFZT
PGWQ
Iconic Memory Experiment
Iconic Memory Experiment
How many letters did you remember?
Typically, people can report only 4 or 5 of
them correctly.
Iconic Memory Experiment
Partial-Report Condition
Your task: Memorize as many letters as possible
in the following display.
Right after the display has disappeared, an arrow
will point to one of the previously shown rows.
Report as many letters as possible that were
shown in that row.
Iconic Memory Experiment
Iconic Memory Experiment
EYHN
GXKF
MQZT
Iconic Memory Experiment
Iconic Memory Experiment
Iconic Memory Experiment
How many letters did you remember
this time?
Often, people can report all four letters.
Iconic Memory Experiment
Partial-Report Condition
Let us do the partial-report condition one more
time, in case you were not prepared the first time.
Iconic Memory Experiment
Iconic Memory Experiment
KCRQ
PVZG
LHXS
Iconic Memory Experiment
Iconic Memory Experiment
Iconic Memory Experiment
You did not know where the arrow was going to
appear; therefore, you must have memorized all 12
letters in order to get all four relevant letters right.
The Sperling experiment thus shows that iconic
memory can hold at least 12 letters.
Other research shows that in fact iconic memory can
hold much more information – a quite detailed
“snapshot” of the visual scene.
However, this information fades very quickly (fast
decay).
Working Memory
Working memory is also known as short-term memory.
It can hold information for longer durations than
sensory memory.
However, its capacity is severely limited.
Working memory can hold multimodal information, i.e.,
acoustic and visual information.
Example: Dialing a phone number that somebody has
just told us.
Working Memory Store
• What happens if you need to keep
information in working memory longer than
30 seconds?
• To demonstrate, memorize the following
phone number (presented one digit at a time):
857916 3
Working Memory Store
• What is the number?
857-9163
The number lasted in your working memory
longer than 30 seconds
So, how were you able to remember the
number?
Maintenance Rehearsal
• Mental or verbal repetition of information
allows information to remain in working
memory longer than the usual 30 seconds
Maintenance Rehearsal
Sensory
Input
Sensory
Memory
Attention
Working or
Short-term
Memory
Maintenance Rehearsal
• What happens if you can’t use maintenance
rehearsal?
• Memory decays quickly
• To demonstrate, again memorize a phone
number (presented one digit at a time)
– BUT, have to count backwards from 1,000 by sevens (i.e.,
1014, 1007, 1000 … etc.)
628509 4
Working Memory Store
• What is the number?
628-5094
Without rehearsal, memory fades
Peterson’s STM Task
• Test of memory for 3letter nonsense
syllables
• Participants count
backwards for a few
seconds, then recall
• Without rehearsal,
memory fades
100
Percentage 90
who recalled 80
consonants
70
60
50
40
30
20
10
0
3
6
9
12
15
18
Time in seconds between presentation
of consonants and recall request
(no rehearsal allowed)
Working Memory Store
• What happens if you need to remember more
than 7 +/- 2 items?
• To demonstrate, memorize the following 16
digit number (presented one digit at a time):
1492181219982001
Working Memory
In a famous paper, Miller (1956) studied the capacity
of working memory.
He found that people can hold about seven
plus/minus two items in working memory.
The problem is: How do you define “item?”
For example, expert chess players can store entire
game configurations in working memory.
Chess novices can memorize the positions of at most
a few pieces.
What is the reason for this? Differences in working
memory?
Chunking
• Grouping small bits of information into
larger units of information
– expands working memory load
• Which is easier to remember?
–4 8 3 7 9 2 5 1 6
– 483 792 516
Working Memory
Chunking
TMCAIADMKSPJDINC
TMC AIADMK
SP
JD
INC
Coding in WM
Conrad’s experiment (1964)
Letters presented visually
Asked to recall immediately
Errors like A for K ; E for P  Acoustic coding
Wicken’s expt. (1972)
Elements of same semantic categories overlap  Semantic
Coding
Visual Coding  Recall time varies with spatial orientation
Three-Box Model of Memory
Long-Term Memory
You can still remember events that happened a long
time ago, for example, when you were a child.
Long-term memory is able to store large amounts of
information over very long durations.
There are several distinct types of long-term memory:
• Procedural memory (Implicit Memory)
• Declarative memory (Explicit Memory)
• Semantic memory
• Episodic memory
Long-Term Memory Store
• Once information passes from sensory to
working memory, it can be encoded into
long-term memory
Maintenance Rehearsal
Sensory
Input
Encoding
Sensory
Memory
Attention
Long-term
Working or
memory
Short-term
Memory Retrieval
Procedural Memory
• Also called implicit memory
• Memory for skill
• Demonstrated only by doing
• Arises without conscious recall
• Examples: Riding a bike, playing tennis, playing the
piano.
Declarative Memory
• Memory for facts and events
• Demonstrated by speaking
• Arises with conscious recall
• Semantic memory:
• Knowledge of facts
• For example, things that you learn in this course
• Episodic memory:
• Contains personally experienced events
• E.g., what you did on your birthday last year.
How long does it last
% recall
1 yr
3 yr
Time
50yr
Remembering Over Years
• Marigold Linton tested her
own memory for personal
events over a period of
several years.
• Retention fell at a gradual but
steady rate.
Long-Term Memory Store
• Function - organizes and stores information
– more passive form of storage than working memory
• Unlimited capacity
• Duration - thought by some to be permanent
Maintenance Rehearsal
Sensory
Input
Encoding
Sensory
Memory
Attention
Long-term
Working or
memory
Short-term
Memory Retrieval
Long-Term Memory Store
• Encoding - process that controls movement
from working to long-term memory store
• Retrieval - process that controls flow of
information from long-term to working
memory store Maintenance Rehearsal
Sensory
Input
Encoding
Sensory
Memory
Attention
Long-term
Working or
memory
Short-term
Memory Retrieval
Encodings
• Different formats
• Implicit Memory  Production rules
– Neural locus of production rules is cerebellum
• Explicit Memory  Network of connected
nodes
– Distributed most likely throughout entire cortex
and other areas.
Conceptual Grid
a memory test...
DOORKNOB
CONCRETE
SUNSHINE
RAILROAD
SOFTBALL
HAMMER
CURTAIN
DOCTOR
SUBWAY
CANDLE
FOLDER
TURKEY
COFFEE
PLAYER
LETTER
TOWEL
KITTEN
MAPLE
PENCIL
TABLE
Serial Position Effects
no
distractor
task
distractor
task
• In free recall, more items are recalled from start of
list (primacy effect) and end of the list (recency
effect)
• Distractor task (e.g. counting) after last item
Serial-Position Effect
• The tendency for recall
of first and last items on
a list to surpass recall of
items in the middle of
the list.
Serial Position Effects
• Explanation from Atkinson and Shiffrin (1968)
model:
– Early items can be rehearsed more often
 more likely to be transferred to long-term memory
– Last items of list are still in short-term memory (with
no distractor task)
 they can be read out easily from short-term memory
How We Remember
Effective Encoding
Rehearsal
Mnemonics
Rehearsal
• Maintenance Rehearsal: Rote repetition of
material in order to maintain its availability in
memory.
• Elaborative Rehearsal: Association of new
information with already stored knowledge
and analysis of the new information to make it
memorable.
Why We Forget
Decay
Replacement
Interference
Cue-dependent Forgetting
Psychogenic Amnesia
Decay
• Decay Theory: The theory that information in
memory eventually disappears if it is not
accessed; it applies more to short-term than
to long-term memory.
Interference
• Retroactive Interference: Forgetting
that occurs when recently learned
material interferes with the ability to
remember similar material stored
previously.
• Proactive Interference: Forgetting
that occurs when previously stored
material interferes with the ability to
remember similar, more recently
learned material.
Cue-dependent Forgetting
• Cue-Dependent Forgetting: The inability to retrieve
information stored in memory because of insufficient
cues for recall.
• State-Dependent Memory: The tendency to
remember something when the rememberer is in the
same physical or mental state as during the original
learning or experience.
Psychogenic Amnesia
• The partial or complete loss of memory (due
to nonorganic causes) for threatening
information or traumatic experiences.
Evaluating Modal Memory Model
• Pro: provides good quantitative accounts of
many findings
• Contra:
– assumption that all information must go through
STM is probably wrong
– Model proposes one kind of STM but evidence
suggests we have multiple kinds of STM stores
Cognitive Architecture of Memory
• Incorporates more details
• Processing power in memory
ACT* Model: Adaptive Control of Thought (Anderson)
External Environment
Encoding
Performance
Working
Memory
Storage
Match
Retrieval
Declarative
Memory
Execution
Production
Memory
The Working Memory Model (Baddeley)
Visuo-spatial Sketchpad
Processing of Visual
Information
Executive Control System
Supervises and controls
processes
Articulatory Loop
Rehearsal and processing of
auditory information
Working Memory Model
• Baddeley (1992)
• 3 interacting components
Visuospatial
Sketch Pad
Central
Executive
Phonological
Loop
Working Memory Model
• Visuospatial sketch pad - holds visual and spatial info
• Phonological loop - holds verbal information
• Central executive - coordinates all activities of working
memory; brings new information into working memory
from sensory and long-term memory
Visuospatial
Sketch Pad
Central
Executive
Phonological
Loop
Baddeley’s working memory
model
Baddeley proposed replacing unitary short-term store
with working memory model with multiple components:
• Phonological loop
• Visuo-spatial sketchpad
• Central executive (ignore the episodic buffer)
Baddeley and Hitch (1974)
Baddeley (1986)
Phonological Loop
(a.k.a. articulatory loop)
• Stores a limited number of sounds – number
of words is limited by pronunciation time, not
number of items
• Experiment:
LIST 1:
Burma
Greece
Tibet
Iceland
Malta
Laos
LIST 2:
Switzerland
Nicaragua
Afghanistan
Venezuela
Philippines
Madagascar
Reading rate determines serial recall
• Reading rate seems to
determine recall
performance
• Phonological loop stores
1.5 - 2 seconds worth of
words
Working memory and Language
Differences
• Different languages have
different #syllables per digit
• Therefore, recall for
numbers should be
different across languages
• E.g. memory for English
number sequences is better
than Spanish or Arabic
sequences
(Naveh-Benjamin & Ayres, 1986)
Two routes to phonological loop
Visual
presentation
Auditory
presentation
Articulatory
control
process
Speech code
Phonological
loop
• Articulatory control process converts visually presented words
into a speech code
• Articulatory suppression (e.g. saying “the” all the time)
– disrupts phonological loop
– diminishes word length effect with visual presentation
(visiospatial sketchpad takes over)
Immediate word recall as a function of modality of
presentation (visual vs. auditory), presence vs. absence
of articulatory suppression, and word length.
Baddeley et al. (1975).
Neural Network Models of
Memory
• Long-term memory:
- weight-based memory; the memory representation
takes its form in the strength or weight of neural
connections
• Short-term memory:
- activity-based memory, in which information is
retained as a sustained or persistent pattern of
activity in specific neural populations
Weight-based memory
• Long-term associative memories can be
formed by Hebbian learning: changes in
synaptic weights between neurons
Donald O. Hebb
Working Memory and Prefrontal
Cortex
Delayed Match to Sample Tasks
• Correct response requires keeping location of food in mind.
• Monkeys and humans w/lesions of PFC fail these tasks.
• Infants younger than 12 months also fail versions of these tasks.
The Hippocampus
Memory
Learning
Navigation
THE HIPPOCAMPUS =
Dentate Gyrus, CA1-CA3, & Subiculum
Marjor input from Entorhinal Cortex
which is  other brain areas such as
the Prefrontal Cortex
Information Flow:
Entorhinal Cortex 
Dentate Gyrus
CA3CA1
Subiculum
Neurogenesis: birth of new neurons
Highly active throughout development
Also adult hippocampal neurogenesis
(dentate gyrus)!
What might this mean for learning and
memory?
Hippocampal Damage
• Retrograde Amnesia: loss of memories before
damage to the hippocampus
• Anterograde Amnesia: inability to form new
memories
• Some causes: aging, Alzheimer’s disease,
stress, temporal lobe epilepsy
Patient H.M.
Patient H.M.
After Surgery for Temporal
Lobe Epilepsy
Anterograde Amnesia:
Intact working and procedural memory
Could not commit to long-term
SOME Retrograde Amnesia:
Couldn’t remember 3–4 -day prior to
surgery, + some events up > 11 years
prior
Able to commit new motor skills to
long-term memory without actually
remembering learning them
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