1. The User
Lecture 2
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2. Overview of Lecture
Introduce human considerations in developing a user interfaces
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3. The user is the most important entity of the system
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4. The User The User Nature of User Human Considerations DeSiaMore

5. Nature of User User Groups Reminder - Computer skills & knowledge
Disabilities
Age
Cultural
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Nature of User

6. The User The User Nature of User Human Considerations DeSiaMore

7. Human Considerations
A vital foundation for HCI designers is an understanding of cognitive and perceptual abilities of the user
Cognition is what goes on in our heads when we carry out everyday activities
There are numerous cognitive frameworks each having different perspectives on cognition
It involves cognitive processes such as perception, attention, memory and learning
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Human Considerations

8. Cognitive Frameworks
Cognitive frameworks help us to understand how users become familiar with a system
2 common frameworks are:
Mental Models
Metaphors
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Human Considerations

9. Cognitive Frameworks - Mental Models
Users develop an understanding of a system through learning & using it
They develop knowledge of:
How to use the system (what to do next)
To a less extent, how the system works
People make inferences using mental models of how to carry out tasks
The more someone learns about a system and how it works, the more their mental model develops
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Human Considerations

10. Cognitive Frameworks - Mental Models
Craik (1943) described mental models as internal constructions of some aspect of the external world enabling predictions to be made
Involves unconscious and conscious processes, where images and analogies are activated
People sometimes uses erroneous mental models
Human Considerations
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11. Cognitive Frameworks - Mental Models
Three Aspects of Mental Models (Norman, 1990):
Design Model is the conceptualisation that the designer has in mind
User Model is what the user develops to explain the operation of the system
System Image – ideally the user and design model are equivalent. However, they communicate only through the system itself
Human Considerations
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12. Cognitive Frameworks - Mental Models
Three Aspects of Mental Models (Norman, 1990):
Design
Model
User
Model
Designer
User
System
System
Image
Human Considerations
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13. Cognitive Frameworks - Metaphors
Another approach to conceptualizing how the mind works has been to use analogies and metaphors
Metaphor is a figure of speech in which an expression is used to refer to something that it does not literally denote in order to suggest a similarity
Human Considerations
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14. Cognitive Frameworks - Metaphors
Most prevalent metaphor – “the mind is an information processor”
Information enters and exits the mind through a series of processing steps
The Human Information Processing (HIP) Model, which provides a basis from which to make predictions about human performance, models the cognitive processes of a user interacting with a computer
Human Considerations
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15. Cognitive Processes Human Considerations DeSiaMore

16. Cognitive Processes Human beings (e.g. users) are very complex
Variety of cognitive attributes have an important influence on screen design
Human Considerations
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17. Cognitive Processes - Perception
Human Considerations
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18. Cognitive Processes - Perception
Perception is fundamental to interacting with computers
To use a computer, a user needs to perceive information that is presented by the interface
Perception can involve all the different senses (visual, hearing, touch, smell..)
To date, mostly concerned with visual perception because screen is usually the interface
Human visual perception has many limitations
Human Considerations
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19. Cognitive Processes - Perception
Classes of Visual
Perception Theory
Techniques to
Guide Perception
Constructive
Ecological
Gestalt Laws
Of Perception
Affordance
Human Considerations
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20. Cognitive Processes - Perception
Two classes of Visual Perception Theory
Constructive
Ecological
Human Considerations
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21. Cognitive Processes – Perception Constructive
Perception involves the intervention of representations and memory
What we see is NOT a replica or copy of the world such as the image that a camera would produce
The visual system constructs a model of the world by transforming, distorting, enhancing and disregarding information
Anything perceived on a screen is also a result of our prior knowledge and expectations
Human Considerations
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22. Cognitive Processes – Perception Constructive Example
Human Considerations
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23. Cognitive Processes – Perception Constructive Example
Once we know what to look for, we recognise the picture
Prior knowledge of what a dalmation looks like helps us to construct the image
Without prior knowledge, we would not able to make sense of the picture
Once we know what the picture depicts it is impossible to perceive it as random dots again, we have a meaningful interpretation
Human Considerations
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26. Cognitive Processes – Perception Constructive Example
The Ruben vase/profile illusion is an ambiguous figure/ground illusion
In this example, one line can have two shapes, depending on which side of the line is regarded as part of the figure
Human Considerations
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28. Cognitive Processes – Perception Constructive Example
This is important as the visual system encodes objects primarily in terms of their contours
Also elements close to one another or alike tend to be grouped together (grouping)
The sudden reversal that you perceive may be due to your shift of attention on the shape of the contours
Stored information that contains knowledge about vases and profiles
Human Considerations
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29. Cognitive Processes – Perception Constructive Example
Another aspect of the constructive process involves using context to interpret and understand what we perceive
Not initially concerned with specific detail, more interested in the overall meaning of the scene
This principle also applies to ambiguous information on computer screens
Human Considerations
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30. Cognitive Processes – Perception Ecological
Ecological theory argues that visual perception is a direct process
Information is simply detected, not constructed
Not really concerned with how we make sense of a scene
Asks what we need to know about our environment in order to carry out our activities
We will actively engage in activities to provide us with the necessary information
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Human Considerations

31. Cognitive Processes – Perception Ecological - Affordance
A central concept of the ecological approach is the notion of affordance
What we see as the behaviour of an object or system is that which is afforded or suggested by the object or system
When the affordance of an object is perceptually obvious (perceptual affordance), it is easy for us to know how to interact with it
When the opposite is true, we tend to make mistakes when trying to interact with the object
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Human Considerations

32. Cognitive Processes – Perception Ecological - Affordance
Scroll bars - intuitive to dragging upwards/downwards
Lip-synch applications – lack of synchronisation disturbs our perception of what is happening
Door handle – good affordance for pushing/ pulling
Pull
Push
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Human Considerations

33. Cognitive Processes – Perception Ecological - Affordance
Affordance is very important with regards to interface objects such as buttons, scrollbars etc. (direct manipulation systems)
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Human Considerations

34. Cognitive Processes – Perception
Techniques used to guide perception
Use of icons and graphical representations
Use of audible, distinguishable sounds
Speech output should enable users to distinguish between set of spoken words
Legible and distinguishable text from its background
Use of tactile feedback in virtual environments
Use perceptual laws of grouping
Use of perceptual boundaries (Windows)
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Human Considerations

35. Summary of Lecture
Human considerations in developing a user interfaces
Cognitive Frameworks
Mental Models
Metaphors
Cognitive Processes
Perception
Attention
Memory
Learning
Conclusion
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36. Terms of Reference Norman, D. (1990) The Design of Everyday Things
Preece, J. et al. (2002) Interaction Design
Shneiderman, B. & Plaisant, C. (2005) Designing the User Interface
Benyon, D. et al (2005) Designing Interactive Systems
Craik, K. (1943) The Nature of Explanation
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References