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Memory

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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.

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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

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“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 __________________________

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“Just the facts” about memory … (cont.)

Differences in memory subsystems (cont.)

Duration

Sensory store _____________________________________

WM _____________________________________________

LTM _____________________________

Codes

Sensory store ____________________

WM ____________________________

LTM ____________________________

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How it works (or doesn’t) ...

Working Memory (WM)

A model (from Baddeley)

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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

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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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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

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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

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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.)

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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

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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?

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Examples ...

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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”

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Examples ...

Physical constraints

Semantic constraints

Cultural constraints

Logical constraints

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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.

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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.

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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.

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What Mr.

Franklin can

figure out

AffordancesPhysical

Constraints

Semantic

Constraints

Logical

Constraints

Cultural

Constraints

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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 ...

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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.

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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.

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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.

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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).

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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.

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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 ...

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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)

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The Performance Operating Characteristic

(POC) curve

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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.

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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.

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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

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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.

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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.

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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

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