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Memory

LONG-TERM MEMORY

WORKING

MEMORY

SENSORY

STORE

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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

http://human-factors.arc.nasa.gov/cognition/tutorials/ModelOf/memory5.html

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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)

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

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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"

"Joseph and the Amazing Technicolor Dreamcoat"

Preamble to the US Constitution

Other approaches to handling WM limitations: Minimize load

Visual “echoes”

Exploit different codes

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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 … (stay tuned - more in the display

design lesson!)– 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 …

Recall the question regarding Benjamin Franklin given to you as homework last week.

1. List a few of the things you’ve thought of that 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 outAffordances

Physical Constraints

Semantic Constraints

Logical Constraints

Cultural Constraints

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ATTENTION!!!

From page 147 of Wickens et al.

ATTENTION RESOURCES

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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)

Performance Operating Characteristic Curve

0

0.5

1

1.5

-0.5 0 0.5 1 1.5

Task A

Tas

k B

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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"

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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