Consistency: A Factor that Links the Usability of Individual Interaction Components Together Willem-Paul Brinkman Brunel University Reinder Haakma Philips Research Laboratories Eindhoven Don Bouwhuis Eindhoven University of Technology

Topics  Research Motivation  Layered Interaction and Consistency  Lab experiments –Experiment 1: inconsistency within the same layer –Experiment 2: inconsistency between layers –Experiment 3: inconsistency and application domain  Conclusions

Research Motivation Do usable components make a usable system? Manage Create Support Reuse Product requirements and existing software new components feedback product component from repository

Layered Interaction & Consistency Interaction component A unit within an application that can be represented as a finite state machine which directly, or indirectly via other components, receives signals from the user. Users must be able to perceive or infer the state of the interaction component.

Layered Protocol Theory (Taylor, 1988)

LOL OTBACK LOL FUN Dictionary Editor Control translation Control word UserTranslator ENTERLL FUN L L LO LOT LO LOL Layered Protocol Theory (Taylor, 1988)

Consistency Definition and interaction component Consistency: Doing similar things in similar ways with agreement between agents about which things are similar (Reisner, 1993). Component Control process Mental model Expectation – feedback Interpretation - feedback

Inconsistency Activation of the wrong mental model

Lab Experiment General Set-Up  48 participants  3 experiments  All participants participated in the 3 experiments  Experiment under the control of one PC application  They were randomly assigned to one of the four conditions in each experiment.

Applications

Component-specific component measures Perceived ease-of-use Perceived satisfaction Objective performance Perceived Usefulness and Ease-of-use questionnaire (David, 1989), 6 questions, e.g.  Learning to operate [name] would be easy for me.  I would find it easy to get [name] to do what I want it to do. Unlikely Likely

Component-specific component measures Perceived ease- of-use Perceived satisfaction Objective performance Post-Study System Usability Questionnaire (Lewis, 1995)  The interface of [name] was pleasant.  I like using the interface of [name]. Strongly disagree agree

Number of messages received directly, or indirectly from lower- level components. The effort users put into the interaction Perceived ease- of-use Perceived satisfaction Objective performance Component Control process Control loop: Each message is a cycle of the control loop Component-specific component measures

Control loop: Each message is a cycle of the control loop Component-specific component measures

Control loop: Each message is a cycle of the control loop Component-specific component measures

Experiment 1: inconsistency within the same layer

Within one layer

Within one layer – Experimental Design Day time Temperature Night time Temperature Moving Pointer Moving Scale Moving Pointer Moving Scale

Within on layer - Results

Experiment 2: inconsistency between layers

Browser Internet Explorer

Experiment 2: inconsistency between layers Text Browser Lynx

Between layers Web-enable TV set Browser versus Web pages

Between layers - Page Layout List layout Matrix layout

Between layers - Browser

Between layers – Experimental Design Web Page Browser List Matrix Linear Plane

Between layers - Results

Experiment 3: inconsistency and application domain

Application Domain Alarm RadioMicrowave The same Timer component in two domains

Application domain

Between Application domain – Experimental Design Application Timer

Application domain - Results

Conclusions & recommendations Conclusion Interaction components in an interactive system can affect each other’s usability because of inconsistencies. Usable components alone do not make a usable system. Recommendation Try to predict component environment, or use a “style guide” Evaluate the component once it is deployed in a new application.

Questions Thanks for your attention