© copyright de montfort university 2000 all rights reserved isde - 1 cognitive aspects of...

ISDE - 1 Cognitive aspects of interactive design © Copyright De Montfort University 2000 All Rights Reserved

Cognitive Psychology & Interface design

Objectives of Lecture

To provide an overview of the key cognitive aspects which influence the design of interactive systems

To illustrate some of these aspects through practical examples

Read Preece Chapter 3


Psychology and Interface Design

• Interaction at the interface is largely a cognitive process

• For effective design can apply knowledge of cognitive psychology

• Need to understand which aspects are important & relevant to interface design

• Can provide information about what the user can and cannot do

• Help explain why uses experience problems with particular interaction /design aspects

• Must remember computers are not used in isolation



• Areas which need to consider include

– Information processing

– Attention

– Visual perception

– Memory

– Mental models



Humans have limitations in each of these but they can perform remarkable feats

• Respond quickly to changing signals

• Make judgements

• Are intuitive

• Solve complex problems

• Deal with the unexpected

• Are versatile


HIP

• The notion of Human Information Processing (HIP) has played a fundamental role in HCI since the 60’s by providing a theoretical basis for cognitive models cognitive models of users

• Problematic in that the model is derived from the architecture of computers themselves

• Alternative models are in development as recognise limitations of HIP model but HIP is still dominant

• (Cognition(Cognition refers to the processes by which humans gain knowledge)


4-stage model of H.I.P

Encoding ComparisonResponseselection

Responseexecution

Memory

Attention

Input orstimuli

Outputorresponse


Extensions to the basic HIP model

• The 4-stage model extends the basic (3-stage) model by the inclusion of

– attentionattention

– memorymemory (considered as an active processprocess rather than a passive store)

• In the extended model cognition is viewed in terms of how:

– information is perceived

– information is attended to

– information is processed and stored in memory


Conscious and Automatic Processing

• A major feature of skilled performance is the ability to perform actions automatically

Extend to the stage model to accommodate

– conscious processing

– automatic processing


Expertise through automatic processing

• design objective is to be make user interface ‘transparent’ to the user

• automatic processing results when knowledge and actions can be compiled into a single internal ‘procedure’

• comes with decreasing reliance on feedback or confirmation of actions by the system

• when there is a change from conscious to automatic processing there is a shift in attentional control from low level ‘concrete’ processes to high level ‘conceptual’ processes


Design requirements

• If a sequence of low level actions are to be carried out automatically, then necessary actions have to be executed without waiting for any intermediate action by system.

• Learning a sequence of actions will be helped if these are meaningful in some way to the user

• What other design implications which must be considered when developing new interactive systems due to users performing some actions automatically?


Attention

• Need to consider certain aspects of attention• Focused and divided attention• Focused Attention - The cocktail party syndrome

– Hearing your name in a crowded room whilst talking to someone– Seeing someone out of the corner of your eye

• In both cases you have been distracted and may have to have the information repeated

• Alternatively can have divided attention. Can carry on conversation and observe what is going on – TV presenters – highly skilled

• We are all capable of this. Can you think of an example?• Attention can also be voluntary or involuntary


Attention

• automatic processing and skill-building

• application to user interface design

• guiding users attention

• memory and design implications

• meaningful interfaces

• recognition vs. recall

• chapter 5 in Preece


Guiding Users Attention at the interface

• Since we know users can be distracted involuntarily we need to consider how we can

– Get their attention again

– Get them to focus on what they should be looking at

Cognitive psychology provides a number of techniques which can be used

• reduce search time by structuring layout so user perceives meaningful components in information

• highlighting through dividers, windows, colour to emphasise structure

• alerting user to new or important information (look at me) using flashing, inverse video, auditory warnings


Guiding Users Attention at the interface

By Location

• location of information on screen guided by its relative importance

– important requiring immediate attention - prominent

– less important - less prominent but in a consistent location

– much less important - not presented but available on request


Memory

• early theories postulated two separate types - long term and short term

• short term memory was demonstrated to have

– finite capacity (7 +/- 2 ‘chunks’ of information)

– finite duration (decays even after 2 or 3 seconds)

– volatile (easily overwritten by by new information)

• capacity could be increased by ‘pattern building’ or encoding

• current theory one type of memory (long term memory)

– parts of memory can be active (working memory)

– rest is inactive


Working Memory

• limited number of items that can be held in an active state at any one time

• the more items held active the lower the activation level for each (leads to longer access time and slower recall)

• the more recently an item has been activated then the more quickly it can be recalled (reactivated)

• retrieval of an item is faster if the category of which item is a member has been activated recently

• if items in memory (long term) are linked into network, reactivating linked items is quicker and easier than other items where links to current active items do not exist


Design Implications

• support user by reducing demands on working memory

• do not require user to remember temporary operating states and labels

• help the user remember how far the current task has progressed

• help the user remember what the system expects them to do next

• leads to the important principle of visibility of current state and feedback about current action

• Think how menus can alleviate memory limitations


Meaningfulness in user interfaces

• meaningful command names aids memory recall and recognition

• recognition refers to the ability to recognise correctly the required command in, say, a menu

• ‘meaningfulness’ depends on category and expertise of user group

• Unix provides examples of ‘unmeaningful’ commands

– e.g. cat, grep, lint, mv, pr, lpr


Meaningful icons

meaningfulness determined by

• context

• function of use

• representational form

• underlying concept


What concepts do these icons represent?

• think about the context in which they might be used


What concepts do these icons represent?

• think again about a unifying context


Icons - Context and function

• context of use limits and directs possible interpretations

– traffic signs, packing cases, email utility,desktop

• function - type of task determines meaningfulness of icons

– to specify and retrieve text better for the domain to be text form rather than graphic or iconic form

– graphic images may be useful for information retrieval task where the user is less sure of the information wanted


Icons - Representational form

• resemblance icons

– uses analogous image to underlying concept

• exemplar icons

–serve as a typical example of concept


Icons - Representational form

• symbolic icons

– uses object at higher level of abstraction to concept being represented e.g fragility

• arbitrary icons

–no relation to underlying concept


Icons - Underlying Concept

• will influence how easy or difficult it will be to devise mappings from domain concepts or items to meaningful graphical images

– files, folders documents have physical counterparts

– danger, hazard, safety, warning do not


Recognition vs. recall

• experts typically do not learn interfaces

• instead they know where information is to be found

• leads to notion of knowledge in the head (recall) and knowledge in the world (recognition)


Visual Perception

• What we see is not what is there!• It is a model of the external world constructed by our

visual system• Our model is constructed based on

– The environment– Our previous experience– Our stored knowledge

• Provides us with a more constant view of the world but must be aware of limitations, different perceptions of individuals, visual illusions


Visual Perception : Illusions


Visual Perception: Impossible Figures


Constructivist Approach to Perception

• Recognition in the comparison stage is:

– a holistic, rather than a serial process e.g Mixed case text is read faster than all UPPER CASE (recognition influenced by shape of word)

– directed semantic interpretation of the whole image, rather than separate perceptions of its component parts

• Recognition directed by schema (assumed data structures within memory) which indicate how to interpret incoming data


Perception - ecological approach

• information is detected rather than constructed

• it asks what we need to know to carry out an activity and how the information is known

• perception is directed by exploring the environment to obtain necessary information as a sequence of activities over time

• objects provide clues or affordances to their function by their appearance

• the more obvious an affordance is, the more easy it is to interact with the object


Affordances

• what actions are suggested by the appearance of the objects?


Relevance to user interface design

• number of areas where information about human perception influences user interface design

– information coding - devices to encode additional information into a display

– creating the illusion of depth


Perception of Depth - Monocular cues

• Motion parallax -when the viewer's head moves, more distant objects appear to move less than closer objects.

• size - the larger of two identical objects appears closer• interposition - an object which partially obscures another object

appears to be in front. • See Preece for further examples


Visual Perception

• Other concerns about perception which the designer must be aware of include:-

• Response time to varying stimuli

• Capacity to identify an object in context

• Colour blindness

• Peripheral Vision

• Flicker sensitivity

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