1 The User Lecture 2 Date: 2 nd February ‘05

2 Overview of Lecture Introduce human considerations in developing a user interfaces

3 The User The user is the most important entity of the system

4 The User Nature of User Human Considerations

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

6 The User Nature of UserHumanConsiderations

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 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 Human Considerations

9 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 Cognitive Frameworks - Mental Models Human Considerations

10 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 Cognitive Frameworks - Mental Models

11 Example: You arrive home on a cold winter’s night to a cold house. How do you get the house to warm up as quickly as possible? Set the thermostat to be at its highest ? Set the thermostat to the desired temperature? Typically, people select to set the heat to its highest setting to “get it to heat up as fast as possible” However, the thermostat will not heat any fasters at a higher setting - erroneous mental model Human Considerations Cognitive Frameworks - Mental Models

12 Other Incorrect Mental Models: Pressing the button at pedestrian lights – more presses, lights will change faster.. Cursor freezes on the computer – press various different types of keys… Hit the TV to make it work.. Voic users assume messages are left on the phone immediately (as opposed to a central system with potential delay in transmitting messages) Human Considerations Cognitive Frameworks - Mental Models

13 Three Aspects of Mental Models (Norman, 1990) : Design Model is the conceptualization 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 Cognitive Frameworks - Mental Models

14 Three Aspects of Mental Models (Norman, 1990) : Human Considerations Cognitive Frameworks - Mental Models Design Model User Model Designer User System Image System

15 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 Cognitive Frameworks - Metaphors

16 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 Cognitive Frameworks - Metaphors

17 EncodingComparison Response selection Response execution Attention Memory Input Stimuli Output Response Conceptual Model Human Considerations Cognitive Frameworks – Metaphors

18 Human Considerations Cognitive Processes

19 Human beings (e.g. users) are very complex Variety of cognitive attributes have an important influence on screen design Human Considerations Cognitive Processes

20 Human Considerations Cognitive Processes - Perception

21 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 Cognitive Processes - Perception

22 Perception Classes of Visual Perception Theory Techniques to Guide Perception Constructive Ecological Gestalt Laws Of Perception Affordance Human Considerations Cognitive Processes - Perception

23 Two classes of Visual Perception Theory Constructive Ecological Human Considerations Cognitive Processes - Perception

24 Theory states that we construct our perception of the world from some of the sensory data falling on our senses 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 Cognitive Processes – Perception Constructive

25 Human Considerations Cognitive Processes – Perception Constructive Example

26 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 Cognitive Processes – Perception Constructive Example

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29 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 Cognitive Processes – Perception Constructive Example

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31 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 This illusion involves higher cortical processing Stored information that contains knowledge about vases and profiles Human Considerations Cognitive Processes – Perception Constructive Example

32 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 Cognitive Processes – Perception Constructive Example

33 Cognitive Processes – Perception Constructive - Gestalt Gestalt laws of perceptual organisation ‘Laws’ of perception that are regarded as being innate Proximity Similarity Closure Continuity Symmetry Human Considerations

34 Cognitive Processes – Perception Constructive - Gestalt Proximity the dots appear as groups rather than a random cluster of elements Human Considerations

35 Cognitive Processes – Perception Constructive - Gestalt Similarity there is a tendency for elements of the same shape or colour to be seen as belonging together Human Considerations

36 Cognitive Processes – Perception Constructive - Gestalt Closure missing parts of the figure are filled in to complete it, so that it appears as a whole circle Human Considerations

37 Cognitive Processes – Perception Constructive - Gestalt Continuity the stimulus appears to be made of two lines of dots traversing each other, rather than a random set of dots Human Considerations

38 Cognitive Processes – Perception Constructive - Gestalt Symmetry regions bounded by symmetrical borders tend to be perceived as coherent figures Human Considerations

39 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 Human Considerations

40 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 Human Considerations

41 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 Push Pull Human Considerations

42 Cognitive Processes – Perception Ecological - Affordance Affordance is very important with regards to interface objects such as buttons, scrollbars etc. (direct manipulation systems) Another type of affordance is sequential affordance This is where acting on one perceptual affordance leads to information indicating new affordances, e.g. when a scrollbar box is clicked, the feedback immediately shows the box in an animated state This affords moving the button up and down The first affordance lends itself to grabbing, the second to dragging Human Considerations

43 Cognitive Processes – Perception Must consider both in screen design Perception ConstructiveEcological Visual scene processed Use memory and experience to make sense of scene Visual scene as is Use information in the scene (affordance) Human Considerations

44 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) Human Considerations

45 Summary of Lecture Conclusion Human considerations in developing a user interfaces Cognitive FrameworksCognitive Frameworks Mental Models Metaphors Cognitive ProcessesCognitive Processes Perception Attention Memory Learning

46 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 References