1 Human Computer Interaction Week 2 Users

2 A Cognitive perspective Cognition: How we gain knowledge These includes: Understanding Remembering Reasoning Attending Being Aware Acquiring Skills Creating New Ideas

3 Human Information Processing Human Information Processing Stages: Encoding Comparison Response Selection Response Execution

4 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.

5 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

6 Sensory Memory Buffers for stimuli received through senses Iconic memory: visual stimuli Echoic memory: aural stimuli Haptic memory: tactile stimuli Continuously overwritten

7 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

8 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

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

10 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.

11 Optical Illusions the Ponzo Illusionthe Muller Lyer Illusion

12 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.

13 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.

14 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

15 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

16 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).

17 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.

18 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).

19 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.

20 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:

21 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

22 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)

23 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

24 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.

25 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

26 Icon Examples a. Resemblance Icon Example b. Exemplar Icon Example c. Symbolic Icon Example d. Arbitrary Icon Example

27 Further Reading Preece, Chapter 3,4,5