Chapter 8 Cognitive psychology Perception By the end

Chapter 8 Cognitive psychology: Perception

By the end of this lecture you should be able to. . . • Describe the different ways of human perception • Explain the – the direct approach – the Gestalt approach – the constructivist approach to perception • Discuss the implications to interactive design of the different approaches • Discuss how cultural and social factors impact the design of interactive systems

Introduction • Knowing how humans are able to perceive the world is fundamental to good design & the creation of usable and accessible systems • Senses: – Vision – Hearing – Other senses • Question: How can we design systems that make the most of users’ perceptual skills and preferences? • Perception will help us understand heuristics like: – “Ease the user’s memory load” – “Recognition rather than recall”

8. 2 Attention • Word attention used in 3 senses: 1. How we make the choice between different stimuli 2. Refers to our capacity to process information 3. Attention often declines over time that we spend on a task

8. 2 Attention and its practical implications for design 1. Attention is selective – We make a choice between different stimuli, some inputs are accepted, other rejected – Interface must be designed that user’s attention is drawn to the important features • Use spacing, colour, size, location, style to attract attention (Discussions on each to follow) 2. Humans are limited with the amount of information that we can deal with (capacity for attention limited) – Don’t bombard people with too much information at once 3. Attention declines over time (limited ability to maintain attention) – Make applications so interesting and attractive as possible

Draw attention: (i)Spacing Designers often fail to consider properly the users of their systems. As a result interactive systems are often difficult to use effectively. In this module you will learn about key cognitive and physical human capabilities and see how such knowledge can be used to build usable and useful systems. The module will introduce a range of user-centred tools, methods and techniques that can be used to complement other software development approaches. Putting white space around something draws attention to it

Draw attention: (ii)Movement Making something move draws attention to it Designers often fail to consider properly the users of their systems. As a result interactive systems are often difficult to use effectively. In this module you will learn about key cognitive and physical human capabilities and see how such knowledge can be used to build usable and useful systems. The module will introduce Making something move draws attention to it a range of user-centred tools, methods and techniques that can be used to complement other software development approaches.

Draw attention: (iii)Colour Designers often fail to consider properly the users of their systems. Putting something in a different colour draws attention to it. As a result interactive systems are often difficult to use effectively. In this module you will learn about key cognitive and physical human capabilities and see how such knowledge can be used to build usable and useful systems. The module will introduce a range of usercentred tools, Particularly red. methods and techniques that can be used to complement other software development approaches.

Draw attention: (iv)Warning • If lots of attention mechanisms get used then they lose their effect. . . • They can be irritating, tiring & hurt the eyes – Particularly movement, flashing and blinking • Make the important things subtly different to everything else

Draw attention: (v)Clarity • Allowing the user to clearly understand what the designer wants. . . – Are icons unambiguous? Zoom? or Find/Replace? – Short, concise sentences. Clear arguments – Users particularly don’t want lots of waffle on computer screens

8. 3 Theories of human perception • Human perception is complex • How and what do we see? – How does the brain process the information captured by the eye? • Three theories 1. Direct or structuralist approach 2. Gestalt approach 3. Constructivist approach

8. 3. 1 Direct (structuralist) approach • Corresponds to our everyday common-sense view of the world • Bottom-up approach: The entire picture is made up of its parts – the perceived object is made of elementary features • Our senses subject an object to increasingly complex analysis of it features and this leads to perception – Visual event defined by location, movement, wavelength, intensity, shape & size

Direct (structuralist) approach (continued) • Structuralism does not explain: – Input to senses varies continually – we perceive unchanged world – We make use of incomplete information – We are selective in the information to which we attend & respond – Visual illusions • Why does grass always appear to be green, whether in shade or in sunlight? • Three types of explanations for visual illusions: – Inference (You know grass is green) – Other sensory events? (E. g. pupil dilation) – Memory involved in perception? (You previously saw grass) • Growing consensus that top-down cognitive processes are also necessary

8. 3. 2 Gestalt • Distinction between external world (objects and events) and internal world (subjective phenomena) • Distinction between sensations (sensory experience) and perception (meaningful interpretation of sensory experience) • Production of perceived objects from sensory experience is carried out automatically by the human nervous system – I. e. our minds creates “wholes” from a collection of attributes

Phenomena of human perception: Gestalt examples(1) – Contextual information • Read the following line – A 13 C D E Sure? – 12 13 14 15 16 • Another line to read – THE DOG AND THE CHT • Context provides meaning! • HCI: X can have 2 meanings depending on the context: • Check box • Close

Phenomena of human perception: Gestalt examples(2) – World Knowledge • Identify the object Using prior knowledge to recognise partial shapes • Edge & contour information vital; colour redundant • HCI: If screen resolution is limited, you may show object in silhouette or only those edges that most clearly define the object

Phenomena of human perception: Gestalt examples(3) – Figure and Ground • Figure & ground = the way we identify an object by distinguishing it from its background • Triangle with a circle on top? or Triangle with circular hole? (Is circle part of the ‘figure’ or part of the ‘ground’? ) • In marking boundaries it is better to use a solid shape than an outline • HCI: Distinguishing between figure & ground is essential if we are to produce pictures and icons that are unambiguous

Gestalt: Affordance • Perception is a direct process – When we encounter stimuli the brain automatically turns collections of features into perceptions • Relationship between user and the system signifying possibility for action – “invitations to act” (giving an indication of what an object can be used for) • Perceived affordance (Donald Norman 1998): – Icons, symbols, objects of interactive systems – They are supported by custom & experience: Not intrinsic – Design interface elements to indicate how they are to be used – Door handles, push buttons, . . .

Gestalt: Affordance(2) • Do interface objects afford their operations? • Can users tell what can be done next with objects? or • Push & pull

Gestalt: Grouping 1. Proximity (we organise the objects we see on the basis of what is near to what) – Rows or columns? • Proximity – Make sense from random arrangements, e. g. the stars forming the Plough

Gestalt: Grouping (2) 2. Similarity • we perceive objects of similar shape or colour to be grouped together 3. Continuity - we organise the objects we see by finding continuous sequences – We see two distinct lines of dots in stead of one shape consisting of dots

Gestalt: Grouping (3) 4. Closure – We see a circle and hexagon rather than three separate lines 5. Symmetry – Areas surrounded by symmetrical lines are recognised as shapes rather than separate lines • Grouping in HCI: Provide designers with hints about how to arrange interface objects so that they will be perceived to belong together in some way

8. 3. 3 Constructivist approaches • Emphasis is on the active, constructive nature of perception • Top-down approach – A human perceives the global image before he tries to break it up into its parts – Building up layers of meaning around a perceived object; a process strongly influences by experience & LTM • HCI: – When designing icons or visual elements, the designer needs a good understanding of users’ prior knowledge. A poor design will mislead users in this process of hypothesizing • Visual illusions can be explained in terms of hypothesis testing process that went wrong

Constructivist approach: Examples of visual illusions • Ambiguous figures – several hypotheses feasible: Young woman or old lady? • Unstable figures: Are the black diamonds the ends of lozenges pointing towards you or the top faces of lozenges pointing downward? • Illusory figures – we ‘see’ a figure that does not exist: Is there a white square in the centre of the image?

Constructivist approach: Examples of visual illusions (2) • Impossible figures – where we ‘see’ a figure that could not possible exist • Apparent movement • - where no real movement exist • Illusory shapes caused by afterimages

Practical Implications for design • Top-down processes (expectations, context, ideas, preferences, biases) – System design should match the expectations and preferences of users • Bottom-up processes – Objects and events should be designed to attract, retain and boost the attention of users – Objects and events be clear that they can easily be understood. • Allow for automatic processes (perceptual habits) – Screen designs should be compatible with users’ habits and automatic responses • Enable users to identify key objects and events on screens • Enable users to develop a stable perception of the system and develop an adequate mental model of it • Users are accustomed to fill gaps of incomplete information automatically – Ensure that your design allow users to fill in the gaps in the right way • Ensure that users can select the right information immediately and respond appropriately

8. 4. 1 Auditory perception • Sound is an important and frequently used medium • Sound plays a central role in: 1. Communicating with other through speech 2. Receiving information and entertainment • radio broadcasts, musical performances, etc. 3. Sound enables us to be aware of events outside our visual field • Police sirens, ringing telephones, etc. 4. Sound give indication of status of environment (even if in background) • E. g. motor car engine, factory noise • Sound has very different set of properties to vision – User could get auditory stimuli from a computer without being in direct contact with it • Sound varies in pitch, timbre, intensity – Computers produce rich variety of sounds • Human ear can only perceive limited range of sounds/differences – 20 Hz-15 KHz; differences of 1. 5 Hz

Properties of sound and vision Vision Sound User control Consists of a number of distinct information tokens. User can decide where he wants to look or decide not to look at all Single information token. User has to listen whether he wants or not (cannot shut your ears) Access time Faster. E. g. user can absorb a large amount of information simultaneously (in parallel). Slower. Audio can only be presented sequentially. Persistence Persistent. Parts previously read remain visible. Non-persistent. If something has been said it is gone for ever. User has to remember. Directionality Directional. Visual sense easily controllable to turning eyes into a particular direction Non-directional. Cannot decide to listen in particular direction Background effects Affected by light. Cannot read a menu in dark restaurant. Affected by noise. Conversation in restaurant with loud background music is difficult.

Sound: Practical implications for design How can sound be used? What for? (See text book as well) 1. Immediate feedback of action, e. g. “beep” as audio alert 2. Presenting different kinds of information to that made available using the visual channel 3. Augmenting interfaces with extra information e. g. ? 4. Users with visual impairments – e. g. voice input (also telephone-based services) 5. Speech synthesis – – Voice as alert; must be able to customise! Voice as information • Interfaces where visual information cannot be presented • Offloading visual display – Users whose visual senses are heavily used e. g. modern aircraft flight decks. e. g. telling a pilot height above the ground during landing so that he does not have to look at altitude display while focusing on the runway ahead

Touch • Haptic feedback – see next slide • Combining input and output using pointing devices: – Joystick, mouse • Data glove – Input/output device used with virtual reality – Senses position, orientation, movement of user’s hand – Allowing gestures to be used as inputs and objects to be grasped – Some add force, pressure, vibration – user ‘feels’ the virtual object they touch/grasp

Haptic feedback • Haptic device is one that involves physical contact between the computer and the user, usually through an input/output device, such as a joystick or data gloves, that senses the body's movements. • By using haptic devices, the user can not only feed information to the computer but can receive information from the computer in the form of a felt sensation on some part of the body. This is referred to as a haptic interface. – For example, in a virtual reality environment, a user can pick up a virtual tennis ball using a data glove. The computer senses the movement and moves the virtual ball on the display.

Data glove Examples

Conclusion. . . • Our perception of things are shaped by the culture in which we grow up • People generally have different ways of perceiving things • There are different ways for the designer to get the user to perceive the important things