User Interfaces

CS 414, Software Engineering IMark Ardis

Rose-Hulman InstituteDecember 10, 2002

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Outline

• Psychology of interfaces• Task analysis• User interface testing methods• Measurement techniques

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User Interface Spiral

Evaluation Analysis

DesignImplementation

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Psychology and Design

• Understand human side of interfaces

• Perception• Attention• Performance• Memory

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Human and the Machine

OutputDevices

InputDevices

HumanInformationProcessor

Computer

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Human Information Processor

Short Term Memory

Long Term Memory

EffectorsSensors

Short TermSensory Store

Ears Eyes Fingers

retrieval

performance

elaboration

attention

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Attention

• Works as a filter for information• Affected by expectations• Multi-modal presentations allow

more information processing

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Performance

• Pointing (selecting) can be predicted by Fitts's Law

• Practice leads to automatic behavior– need for attention drops

• Action slips– caused by inattention

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Fitts's Law

Movement Time = a + b IDID = log2 ( 2A / W )

A = amplitude (size of movement)W = width of targetID is the index of difficultya, b are constants

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Memory

• Short Term Sensory Store - 100 msec• Short Term Memory - 15 sec

7 2 chunks• Long Term Memory

– proactive interference• hard to learn a new system

– retroactive interference• hard to return to an old system

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Working Memory

• Users need to retain several different types of information in order to accomplish a task

• There is a limit to amount of information that can be recalled easily

• Designers need to break up complicated tasks into sequences of simpler tasks

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Conceptual Models

• Abstraction of system• Simple enough for non-technical

users• Often described by analogy

– clipboard for copied text– folder for collection of files

• Should be made explicit

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Outline

• Psychology of interfaces• Task analysis• User interface testing methods• Measurement techniques

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Task Analysis

1. Observe users in their natural habitat

2. Interview users3. Write down sequences of actions

required to accomplish tasks4. Refine and categorize actions

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Example Task Analysis

Example: Correcting a manuscript

1. Find location of change– Scroll document– Move cursor

2. Delete old text3. Insert new text

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Screen Layout1. Collect a set of scenarios (use cases)2. Describe each scenario with

sequence of tasks from task analysis3. Identify actions (verbs) and objects

(nouns)4. Draw screen layouts showing objects5. Simulate actions

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Guidelines

• Several good books available• Some guidelines in Pressman:

– Place the user in control– Reduce the user's memory load– Make the interface consistent

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Place the User in Control

• Provide for flexible interaction• Allow interruption and undo• Allow customization• User direct manipulation of screen

objects

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Prototyping

• Useful for creating screen layouts• Allows feedback from users• Provides starting point for User

Manual

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Cartoon of the Day

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Outline

• Psychology of interfaces• Task analysis• User interface testing methods• Measurement techniques

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UI Testing Methods

• Experiments• Interviews• Observation• Heuristic evaluation• Focus groups• Input logging• Surveys

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Experiments

• Useful for testing alternatives• Requires expert to construct

– need to use appropriate experimental design

– need to control variables

• Used during design

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Interviews

• Useful for collecting requirements and for spot-checking other results

• Require planning– use a standard list of questions– allow open-ended questions

• Analysis may be hard

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Observation

• Useful for learning about "real environment" use

• Should be planned– identify behaviors of interest– use multiple observers to categorize

behaviors

• May be intrusive or blind

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Heuristic Evaluation

• Experts examine a product and produce scores for each principle of good design

• Cheap and easy to perform• Biased by expert opinions

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Focus Groups

• Moderated interview of several potential users (1-2 hours)

• Useful when product is unavailable, or its use is uncommon

• Moderator presents scenarios, or descriptions of a product, or only a concept

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Input Logging

• Instrumentation used to collect data from use

• Many types of measurements:– frequency– time– errors

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Surveys

• Useful for longitudinal studies• Depends on accuracy of sampling

– volunteer surveys tend to be more positive than general population

– rewards may be used to encourage participation

• Good method for collecting attitudinal data

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Users Needed

• Experiments: > 10• Interviews: 5-10• Observation: 3-5• Heuristic evaluation: 0 (need experts)• Focus groups: 6-9/group• Input logging: > 20• Surveys: 100s

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Outline

• Psychology of interfaces• Task analysis• User interface testing methods• Measurement techniques

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Measurement Techniques

• Questionnaires• Performance measures• Thinking aloud• Audio-video recording

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Questionnaires

• Cheap to implement, may be reused• Require careful design

– need to be of appropriate length– need to calibrate scales– may duplicate questions to check

validity

• Useful for surveys, experiments and interviews

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Performance Measures

• Objective measures– reaction time– accuracy– frequency

• Useful for input logging and experiments

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Thinking Aloud

• Subject thinks out loud while using product

• May also be done as a coaching session

• Useful for experiments and interviews

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Audio-video Recording

• Videotape user in action• Collects a lot of important

information• May collect too much information• Useful for experiments and

observation

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Good and Bad Examples

Yale Web Style Guide:http://info.med.yale.edu/caim/manual

Interface Hall of Shame:http://www.iarchitect.com/mshame.htm

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Quiz!