1. CEN3722 Human Computer Interaction Cognition and Perception
Dr. Ron Eaglin

2. Objectives
Understand the importance of perception and cognition in HCI
Describe models of cognition (cognition frameworks)
Understand factors affecting perception
Context
Graphical Coding
Color
Images
Depth
Describe how representation influences perception

3. Conflicting Visual Cues
Example of Poor Design
Conflicting Visual Cues

4. Cognition
Cognition refers to how we gain knowledge
Objective of HCI:
Understand and represent how humans and computers interact in the transmission of knowledge (paraphrased from Preece, et.al. 1996)

5. Understanding Cognitive Process
Allow us to predict how humans will perceive, think and act.
Prediction allows for design
Elements of cognition
Remembering
Reasoning
Awareness
Skill development
Generating (new) ideas

6. Stages of Information Processing
Encoding
Comparison
Response
Selection
Execution
Each stage takes time and this is unidirectional and sequential

7. Stages - Encoding
Hot
Flame
Ouch!
Encode information from environment into mental representation

8. Stages - Comparison
Internal representation of the stimulus is compared with memorized representations stored in the brain (long-term memory)

9. Stages – Response Selection
Deciding upon a response
to coded stimuli

10. Stages – Response Execution
Organization of response and
necessary action

11. Stages of Information Processing

12. Multi-store Memory Model

13. Memory Model
Sensory Store – External stimuli registers in modality (visual, auditory, tactile) store.
Working Memory – Holds limited information for a few seconds.
Long Term Memory – Holds information indefinitely, practice required for complex tasks migrating to long term.

14. Theories of Visual Perception
Constructive theory
Perception is an active process, where the world is constructed from information in the environment and previously stored knowledge.
Ecological theory
No active process involved – simply absorb information from the environment.

15. Importance of Context
Adapted from Selfridge, © IEEE

16. Importance of Context H A
Context is fundamental to interacting with computers, because it affects how we perceive objects.
Context and prior knowledge allow us to interpret same symbols differently H A

17. Similarity
Proximity
Similarity
Closure
Continuity
Symmetry

18. Graphical Representation
May seem desirable to present information on the screen that has characteristics similar to the objects we perceive in the environment
The visual system could then use the same processes that it uses when perceiving objects in the environment.

19. Perceptual Depth Cues
Size - larger of two identical objects appears closer
Interposition - a visually blocked object appears to be behind the blocking object
Contrast, clarity and brightness - sharper, more distinct items appear nearer
Shadows - indicate relative position
Texture - more apparent in closer objects

20. 3-D Cues

21. Graphical Coding
Abstract systems, data objects, and other features of the interface can be represented by different forms of graphical coding
Direct mappings are best: analogy in real-world
Different icon sizes to reflect size of file
Different line widths to represent increasing draw size
Bar charts to show trends in numerical data
Wastebasket to represent place for unwanted files

22. Color Coding Powerful way of dividing display into separate regions
Useful for search tasks
spotting an object in a list, but of less use for tasks requiring categorization or memorization
too many colors will increase search times
More effective with inexperienced users

23. Color Coding

24. Color Rules - example

25. Use of Color and Contrast
Bad
Bad OK

26. Icons Used to represent system objects, application tools, etc.
Increasingly used at the interface for a range of systems
Advantage: can reduce complexity of the system by making it easier to use
Allow perceptual processes to take over.
Problem: difficult to map meaning to image
Especially for abstract actions: search, replace, undo, redo
Concrete actions: save, print, cut, copy (?)

27. Lesson Summary You should now understand:
The importance perception and cognition play in HCI
Models of cognition (frameworks)
How perception is influenced or used through
Context
Graphical coding
Color
Graphical images (icons)
Perceptual (monocular) depth cues