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1
Memory
ISE 4121
LONG-TERM MEMORY
WORKING
MEMORY
SENSORY
STORE
A little experiment in memory …
Courtesy of NASA Ames Cognition Laboratory (http://human-
factors.arc.nasa.gov/cognition/tutorials/ModelOf/memory5.html)
Step 1: take out a blank sheet of paper and put “List 1” on the top.
Then put your pencil/pen down.
Step 2: listen to the list of words carefully.
Step 3: after the entire list is finished, you will be instructed to write
down as many of the words as you can remember.
Step 4: check your list against the one I show you and write the
number correct at the top of the page.
Repeat steps 1 – 4 with List 2 and List 3.
ISE 4122
2
Results from an earlier experiment
ISE 4123 http://human-factors.arc.nasa.gov/cognition/tutorials/ModelOf/memory5.html
Impact of memory on system design ...
Power:
Vast store of knowledge
Limitations:
Forgetting
Limited working memory
Attention
ISE 4124
3
“Just the facts” about memory ...
Three subsystems of memory:
Short-term sensory store
Working memory (short-term memory) –WM/STM
Long-term memory - LTM
These subsystems differ in several ways
Capacity
Sensory store __________________________________
WM is ______________________________
• (the "magic number" 7 plus or minus 2)
LTM __________________________
ISE 4125
“Just the facts” about memory … (cont.)
Differences in memory subsystems (cont.)
Duration
Sensory store _____________________________________
WM _____________________________________________
LTM _____________________________
Codes
Sensory store ____________________
WM ____________________________
LTM ____________________________
ISE 4126
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How it works (or doesn’t) ...
Working Memory (WM)
A model (from Baddeley)
ISE 4127
Central
Executive
Phonological LoopVisuospatial Sketchpad
• Stored in analog spatial form
• From visual sensory system or
LTM
• Stored in acoustical form
• Info kept active through
rehearsal
WM: How it works (or doesn’t) ...
Restrictions:
Capacity - 7 + 2 “items” of information.
Time - 7 - 70 second “half-life”
Some solutions ...
Increase capacity by “chunking”
Create meaningful sequence already present in LTM
Experiments:
– Subject could recall > 20 binary digits by coding into octal (0101111 57)
– Subject could recall > 80 digits by coding into running times (353431653
3 min, 53.4 sec mile; 3 hr, 16 min, 53 sec marathon)
– Chess masters recall board with great accuracy; "chunk" into strategic
patterns
ISE 4128
5
WM: How it works (or doesn’t) ... Examples of everyday chunking:
Parsing - break up into chunks
phone numbers, social security numbers
Reading musical staffs ("Every Good Boy Does Fine")
Medical school mnemonics
Songs: constraints of rhythm, rhyme
"We Didn't Start the Fire"
Preamble to the US Constitution
Oral history / epic poetry
Other approaches to handling WM limitations:
Minimize load
Visual “echoes”
Exploit different codesISE 4129
How it works (or doesn’t) ...
Long-term memory (LTM)
Types
Semantic memory - general knowledge
Event memory
Episodic - an event in the past
Prospective - remember to do something
Basic mechanisms:
Storage - through active rehearsal, involvement, or link to an existing memory.
Alternatively - “everything gets in”
Retrieval - depends on
item strength
number and strength of associations to other items
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6
LTM: How it works (or doesn’t) ...
Organization of information in LTM
Most-used information is semantic
retrieval depends on semantic associations
good design builds / uses appropriate semantic associations
The network of semantic associations around specific topics are
schemas
Schemas involving sequences of activities are scripts
Schemas concerning how equipment and systems work are mental models
ISE 41211
LTM: How it works (or doesn’t) ...
What it means for design …
Encourage regular use of info
Standardize
Design information to be remembered
Provide memory aids
ISE 41212
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Memory versus knowledge “in the world”
When do you not need to remember something?
(Why do you not need to remember what a penny looks like?)
When the knowledge is already "in the world"!
(Because you only need to recognize a penny - and nothing else
looks like it.)
ISE 41213
Knowledge “in the world”from Norman, D.A. The Design of Everyday Things, (formerly "P.O.E.T.") 1988. New York: Currency/
Doubleday.)
Affordances
Constraints
Mappings
Conceptual Models
Visible Structure
Reveals:
– 1. affordances
– 2. constraints
– 3. mappings
ISE 41214
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Affordance
"refers to perceived or actual properties of the thing, primarily
those fundamental properties that determine just how the thing
could possibly be used.” (Norman, pg. 9)
Affordances of objects: e.g., chairs, tables, cups
Affordances of materials: e.g., glass, wood
Affordances of controls: How are things operated?
ISE 41215
Examples ...
ISE 41216
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Constraints
Those aspects of a device or material that limit its perceived possible uses.
Physical: size, shape, possibilities for movement, etc.
Semantic: meaning of the situation related to the notion of “conceptual models”
Cultural: defined by tradition, meaning within the culture (e.g., the color red, triangular shape)
Logical: placement of controls, direction of movement, etc. related to “mappings”
ISE 41217
Examples ...
Physical constraints
Semantic constraints
Cultural constraints
Logical constraints
ISE 41218
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Conceptual Models
Our understanding of the way things work, how things are put
together, cause & effect, etc.
Depends on the visibility of the system structure, the timing of the
feedback, and consistency of cause/effect relationships
Builds a framework for storing knowledge about a system or device
“in the head.”
Used to develop explanations, recreate forgotten knowledge, and
make predictions.
ISE 41219
Mappings
Making the connection between how things work and how we
think they work.
Some examples (recall the display design lessons) …
– Principle of Pictorial Realism: Displayed quantities should correspond to the
human's internal model of these quantities.
– Congruence: The linear motion of a control and display should be along the
same axis and the rotational motion of a control and display should be in the
same direction.
– Principle of the Moving Part: The direction of movement of an indicator on a
display should be compatible with the direction of movement of an operator's
internal representation of the variable whose change is indicated.
– Spatial compatibility: The spatial arrangement of displays should be preserved in
the controls.
ISE 41220
11
Your turn …
Imagine that Benjamin Franklin has been transported to
your apartment. Given his legendary inquisitiveness, spend
a few minutes discussing:
1. What would Mr. Franklin would be able to “figure out” in
your apartment/home.
2. Describe how Mr. Franklin is able to figure these things out
in terms of the affordances, constraints, mappings, and
visible structure.
Use the following table to help organize your answer.
ISE 41221
What Mr.
Franklin can
figure out
AffordancesPhysical
Constraints
Semantic
Constraints
Logical
Constraints
Cultural
Constraints
ISE 41222
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ATTENTION!!!
ISE 41223From page 147 of Wickens et al.
ATTENTION RESOURCES
ATTENTION!!!
A "flexible, sharable, processing resource of limited availability".
Our ability to attend to several things at once (time-sharing)
depends on:
Controlled vs automatic processing
Skill
Which resource(s) required
Attention “tasks” can be divided into 4 categories ...
ISE 41224
13
1. Selective Attention
"requires the monitoring of several channels (sources) of information to
perform a single task.”
Example: scanning cockpit instruments
Limitations:
– As the number of channels of information increases, performance declines (even
when the overall signal rate is the same).
– Can select inappropriate aspect(s) of the environment to process.
– "Cognitive tunnel vision" in complex environments with many displays, especially
under stress. (Example: 1972 Eastern Airlines crash in the Everglades).
Errors associated with Selective Attention are generally the result of an
intentional, but unwise choice.
ISE 41225
Selective Attention
Design Guidelines:
Place frequently sampled displays together.
Place sequentially sampled displays together.
Use external aids/reminders to help people remember when the display was
last sampled.
ISE 41226
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2. Focused Attention
Requires attending to one source of information at the exclusion of all
others
Examples:
Trying to study while someone else is talking on the phone
Trying to enter numerical data into Excel while others are discussing basketball scores
and stats.
Limitations:
Impossible to ignore a visual stimulus within 1 degree of visual angle of the visual
information you are interested in.
Auditory stimuli sufficiently loud with respect to the signal you are interested in,
and/or similar to it, can interfere with the signal.
Errors associated with focused attention are generally unintentional,
driven by the environment.
ISE 41227
Focused Attention
Design Guidelines: Parallel vs serial processing
Parallel processing is helpful when: two tightly coupled tasks are performed simultaneously (e.g., control roll and pitch of
aircraft)
two or more information sources imply common action (redundancy gain)
Parallel processing is harmful when similar aspects of different stimuli must be processed (resource competition)
two or more stimuli imply different actions
e.g., a batter distracted by a moth
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3. Sustained Attention
"the ability of observers to maintain attention and remain alert over
prolonged periods of time."
Example: Security guard watching monitor for intruders.
Limitations:
Vigilance decrement - a decline in the speed and accuracy of signal detection
with time on the task (found more in the laboratory than in real world tasks).
ISE 41229
Sustained Attention
Design Guidelines:
Appropriate work-rest schedules and task variation.
Increase the conspicuity of the signal.
Reduce uncertainty as to when and where.
Training.
ISE 41230
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4. Divided Attention
"two or more separate tasks must be performed at the same time, and
attention must be paid to both.”
Example: Driving and talking to a passenger.
Limitations:
Time-sharing ...
ISE 41231
The Resource Metaphor of Attention
Time-sharing (or doing two tasks simultaneously) is difficult because
we have limited attention resources.
The Performance-Resource Function (PRF)
ISE 41232
17
The Performance Operating Characteristic
(POC) curve
ISE 41233
Performance Operating Characteristic Curve
0
0.5
1
1.5
-0.5 0 0.5 1 1.5
Task A
Task B
Limitations of the "single-resource" theory
of attention
Difficulty insensitivity
In some experiments it has been shown that making one time-shared task more
difficult has no effect on the performance of the other.
Perfect time-sharing
Structural alteration effects
In some experiments it has been shown that altering the structure (but NOT the
difficulty) of one task affects performance on the other.
Example: Manual vs vocal responses to a tone discrimination task while tracking.
ISE 41234
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Multiple-resource theory
Instead of one "pool" of resources, there are several different capacities
of resources:
Codes: spatial or verbal
Modalities: visual or auditory
Stages of processing: early (encoding/central processing) or late (responding)
The more resources are shared, the more tasks will interfere.
ISE 41235
Multiple-resource theory
To the extent that tasks demand separate rather than common
resources:
Time-sharing will be more efficient
Difficulty insensitivity will be observed
The POC will be more "boxy"ISE 41236
MODALITIES
Visual
Auditory
Codes
Spatial
Verbal
RESPONSESManual
Vocal
STAGES
Encoding Central Processing
Response
19
Limitation of multiple resource theory
The three proposed dimensions (stages, codes, modalities) do not
account for all experimental findings. For example:
Tasks with different rhythmic requirements are hard to time-share.
Control dynamics affect the efficiency of time-sharing a manual tracking task with
another task.
ISE 41237
Implications & design recommendations
Since spatial and verbal codes draw upon separate resources, time-
sharing manual and verbal responses is highly efficient (assuming that the
manual response is spatial in nature and that the vocal response is
verbal). Example:
pilots fly the airplane (spatial, manual task) and simultaneously talk to air traffic
control (verbal, vocal task).
This example also demonstrates different modalities (visual and auditory) which
also draw from separate resources;
therefore …
Design systems to support a mix of manual and vocal responses for time-
shared tasks.
ISE 41238
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Multiple resource theory
The effect of training
Training can make tasks data limited rather than resource limited
Data limited tasks can coexist more easily than resource-limited
Reasoning behind “part-task training” paradigms
People can also be trained to timeshare tasks more efficiently
Rapid switching between tasks
True multi-tasking
ISE 41239