UI Evaluation: Cognitive Walkthrough. CS-E5220 User Interface Construction

Transcription

1 UI Evaluation: Cognitive Walkthrough CS-E5220 User Interface Construction

2 Usability Testing With users Usability test Without users Heuristic evaluation Cognitive walkthrough

3 Nielsen s Ten Heuristic Rules (1993) 1. Simple and natural dialog 2. Speak the user s language 3. Minimize user s memory load 4. Consistency 5. Feedback 6. Clearly marked exits 7. Shortcuts 8. Good error messages 9. Prevent errors 10. Help and documentation

4 User Interface: Mediator for the Input / Output between subsystems Input Information flow User System Functionality Output Human subsystem Interface Computing subsystem

5 Usability (ISO ) User Intended outcome Goals Task Usability Tools Effectiveness Surroundings Context of Use Result of interaction Efficiency Satisfaction Product Usability metrics

6 Interaction with UI: Seven Stages 1 Goals 2 Intent 7 Evaluation 3 Formation of action/sequence 6 Interpretation 4 Execution Execution Gulfs Evaluation 5 Perception, Observation System / External World / User Interface Norman 1986

7 Cognitive Walkthrough Formalized way of imagining people's thoughts and actions when they use an interface for the first time. First select a task that the design is intended to support. Then try to tell a believable story about each action a user has to take to do the task. To make the story believable, you have to motivate each of the user's actions, relying on the user's general knowledge and on the prompts and feedback provided by the interface. If you can't tell a believable story about an action, then you've located a problem with the interface.

8 What s it good for? Question assumptions about what the users will be thinking Identify controls that may be missing or hard to find Note inadequate feedback Suggest difficulties with labels and prompts The Vocabulary Problem

9 Vocabulary Problem On a piece of paper write the name you would give to a program that tells about interesting activities occurring in some major metropolitan area (e.g., this program would tell you what is interesting to do on Friday or Saturday night). Make the name 10 characters or less

10 Why do we have issues? Armchair naming. Designers use names that make sense to them. In a study to determine the likelihood that two people will apply the same name to an object: Personnel Domain % Typists Describe text editing operation 11% System Designers Commands for a message decoder 8% College students First word used to describe common 12% objects like love, motorcycle Expert cook/homemaker Recipe keyword 18%

11 Cognitive Walkthrough Purpose Focus most clearly on problems that users will have when they first use an interface, without training Not a technique for evaluating the system over time (e.g., how quickly a user moves from beginner to intermediate) Most effective if designers can really create a mental picture of the actual environment of use

12 How to do it Prior to doing a walkthrough, you need four things: 1. You need a description of a prototype of the interface. It doesn't have to be complete, but it should be fairly detailed. Things like exactly what words are in a menu can make a big difference. 2. You need a task description (for a representative task). 3. You need a complete, written list of the actions needed to complete the task. 4. You need an idea of who the users will be and what kind of experience they'll bring to the job.

13 Some caveats The walkthrough should look at the exact sequence to identify problems users might encounter when following it. The walkthrough does not test real users on the system. With a walkthrough you can potentially evaluate the interface by imagining the behavior of entire classes of users, not use one unique user.

14 Cognitive Walkthrough

15 CW: Questions to ask 1. Will the users be trying to produce whatever effect the action has? 2. Will users be able to notice that the correct action is available? 3. Once users find the correct action at the interface, will they know that it is the right one for the effect they are trying to produce? 4. After the action is taken, will users understand the feedback they get? For each question, make remarks on problems and elaborate on / propose improvements