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Human Computer Interaction

Week 2Users

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A Cognitive perspective

Cognition: How we gain knowledge These includes:

Understanding Remembering Reasoning Attending Being Aware Acquiring Skills Creating New Ideas

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Human Information Processing

Human Information Processing Stages: Encoding Comparison Response Selection Response Execution

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Information Processing and HCI Human Processor Model (Card et al,

1983): The Perceptual System The Motor System The Cognitive System

Human Processor Model provides a means of characterizing the various cognitive processes that are assumed to underlie the performance of a task.

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Human’s Memory

There are three types of memory function:Sensory Memory

Short-term / Working Memory

Long-term Memory

Selection of stimuli governed by level of arousal

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Sensory Memory

Buffers for stimuli received through senses Iconic memory: visual stimuli Echoic memory: aural stimuli Haptic memory: tactile stimuli

Continuously overwritten

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Short-term Memory (STM)

Scratch-pad for temporary recall Rapid access ~ 70 ms Rapid decay ~ 200 ms Limited capacity ~ 7 ± 2 chunks (Miller,

1956)

Example 2126985697 212 698 5697

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Long-term Memory (LTM) Repository for all our knowledge

Slow access ~ 1/10 second Slow decay, if any Huge or unlimited capacity

Two types Episodic – serial memory of events Semantic – Structured memory of facts,

concepts, skills Semantic LTM derived from episodic LTM

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Vision

Two stages in vision Physical reception of stimulus Processing and interpretation of

stimulus

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Visual Perception

Perception is an active process Two perception theories:

Constructivist approach: has been used to inform the design of information displays to make information stand out and be readily perceivable.

Ecological approach: has been used to inform the design of interface objects in terms of how they afford the actions that are intended to be performed on them.

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Optical Illusions

the Ponzo Illusion the Muller Lyer Illusion

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Graphical Coding Color Coding (not color pollution) Effectiveness of color coding in

cognitive tasks: searching and Identifying targets (Davidoff, 1987): Segmentation (region division). Amount of color (more color, more search

time). Task demand (best for search task, not

categorization and memorization of objects).

Experience of user (color is more useful for inexperienced than for experienced users.

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Color Coding (Travis, 1991) Color is a useful coding mechanism for

grouping: use different colors to distinguish layers (e.g. front and back layers).

Color makes things stand out: use color to make features prominent (e.g. currently active files could be colored in orange).

Figure/background: Dark or dim backgrounds should be used, such as deep blue, and bright colors for the foreground.

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Hearing Provides information about environment:

distances, directions, objects, etc. Physical apparatus:

Outer ear – protects inner and amplifies sound Middle ear – transmits sound waves as vibrations

to inner ear Inner ear – chemical transmitters are released and

cause impulses in auditory nerve Sound

Pitch – sound frequency Loudness – amplitude Timbre – type of quality

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Hearing (cont.)

Humans can hear frequencies from 20 Hz to 15 kHz Less accurate distinguishing high

frequencies than low Auditory system filters sounds

Can attend to sounds over background noise

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Focusing Attention

Our ability to attend to one event from what amounts to a mass of competing stimuli in the environment has been termed as focused attention.

For example: Cocktail Party phenomenon (Cherry, 1953).

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Divided Attention

When we attempt to attend to more than one thing at a time.

For example: being able to drive while holding a

conversation with a passenger. Being distracted from working when

we can hear music or voices in the next room.

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Focusing attention at the interface

Structuring Information so that it is easy to navigate through: Presenting not too much information and

not too little on a screen. Grouping and Ordering.

Other Techniques for guiding attention: Spatial and Temporal Cues. Color. Alerting Techniques (flashing, reverse video,

auditory warnings).

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Automatic Processing Automatic Cognitive Processes are

identified as: Fast. Demanding Minimal Attention and hence

not interfering with other activities. Unavailable to consciousness.

Example: Reading, Writing, Speaking in Native

Language, Riding a bike.

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Automatic Cognitive Process (Example)

ZYP QLEKF SUWRG XCIDB WOPR ZYP QLEKF

RED BLACK YELLOW BLUE RED GREEN YELLOW

The Stroop Effect (Gleitman, 1991): See how long it takes you to name the colors of the items in the two lists of words below. Try to say them as quickly as possible:

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Emotion Various theories of how emotion works

James-Lange: emotion is our interpretation of a physiological response to a stimuli

Cannon: emotion is a psychological response to a stimuli

Schacter-Singer: emotion is the result of our evaluation of our physiological responses, in the light of the whole situation we are in

Emotion clearly involves both cognitive and physical responses to stimuli

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Emotion (cont.) The biological response to physical

stimuli is called affect Affect influences how we respond to

situations Positive: Creative problem solving Negative: Narrow thinking

Negative affect can make it harder to do even easy tasks; positive affect can make it easier to do difficult tasks (Donald Norman)

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Emotion (cont.)

Implications for interface design Stress will increase the difficulty of

problem solving Relaxed users will be more forgiving

of shortcomings in design Aesthetically pleasing and rewarding

interfaces will increase positive affect

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Designing meaningful command names

Trend: highly abstract, arbitrary Names were chosen due to their

efficiency (e.g. Function keys) General guidelines for the

selection of command names: consider the contextual, cultural, and user characteristics.

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Designing meaningful icon

Icon Classification (Rogers, 1989): Resemblance Icons: analogous image Exemplar Icons: typical example Symbolic Icons: higher level of

abstraction Arbitrary Icons: association has to be

learned

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Icon Examples

a. Resemblance Icon Exampleb. Exemplar Icon Examplec. Symbolic Icon Exampled. Arbitrary Icon Example

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Further Reading

Preece, Chapter 3,4,5