User Interfaces CS 414, Software Engineering I Mark Ardis Rose-Hulman Institute December 10, 2002

2 Outline Psychology of interfaces Task analysis User interface testing methods Measurement techniques

3 User Interface Spiral Evaluation Analysis Design Implementation

4 Psychology and Design Understand human side of interfaces Perception Attention Performance Memory

5 Human and the Machine Output Devices Input Devices Human Information Processor Computer

6 Human Information Processor Short Term Memory Long Term Memory EffectorsSensors Short Term Sensory Store EarsEyesFingers retrieval performance elaboration attention

7 Attention Works as a filter for information Affected by expectations Multi-modal presentations allow more information processing

8 Performance Pointing (selecting) can be predicted by Fitts's Law Practice leads to automatic behavior –need for attention drops Action slips –caused by inattention

9 Fitts's Law Movement Time = a + b ID ID = log 2 ( 2A / W ) A = amplitude (size of movement) W = width of target ID is the index of difficulty a, b are constants

10 Memory Short Term Sensory Store 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

11 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

12 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

13 Outline Psychology of interfaces Task analysis User interface testing methods Measurement techniques

14 Task Analysis 1.Observe users in their natural habitat 2.Interview users 3.Write down sequences of actions required to accomplish tasks 4.Refine and categorize actions

15 Example Task Analysis Example: Correcting a manuscript 1.Find location of change –Scroll document –Move cursor 2.Delete old text 3.Insert new text

16 Screen Layout 1.Collect a set of scenarios (use cases) 2.Describe each scenario with sequence of tasks from task analysis 3.Identify actions (verbs) and objects (nouns) 4.Draw screen layouts showing objects 5.Simulate actions

17 Guidelines Several good books available Some guidelines in Pressman: –Place the user in control –Reduce the user's memory load –Make the interface consistent

18 Place the User in Control Provide for flexible interaction Allow interruption and undo Allow customization User direct manipulation of screen objects

19 Prototyping Useful for creating screen layouts Allows feedback from users Provides starting point for User Manual

20 Cartoon of the Day

21 Outline Psychology of interfaces Task analysis User interface testing methods Measurement techniques

22 UI Testing Methods Experiments Interviews Observation Heuristic evaluation Focus groups Input logging Surveys

23 Experiments Useful for testing alternatives Requires expert to construct –need to use appropriate experimental design –need to control variables Used during design

24 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

25 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

26 Heuristic Evaluation Experts examine a product and produce scores for each principle of good design Cheap and easy to perform Biased by expert opinions

27 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

28 Input Logging Instrumentation used to collect data from use Many types of measurements: –frequency –time –errors

29 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

30 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

31 Outline Psychology of interfaces Task analysis User interface testing methods Measurement techniques

32 Measurement Techniques Questionnaires Performance measures Thinking aloud Audio-video recording

33 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

34 Performance Measures Objective measures –reaction time –accuracy –frequency Useful for input logging and experiments

35 Thinking Aloud Subject thinks out loud while using product May also be done as a coaching session Useful for experiments and interviews

36 Audio-video Recording Videotape user in action Collects a lot of important information May collect too much information Useful for experiments and observation

37 Good and Bad Examples Yale Web Style Guide: Interface Hall of Shame:

38 Quiz!