Reasoning about order errors in interaction

Reliability of an interactive system depends on users as well as the device implementation. User errors can result in catastrophic system failure. However, work from the field of cognitive science shows that systems can be designed so as to completely eliminate whole classes of user errors. This means that user errors should also fall within the remit of verification methods. In this paper we demonstrate how the HOL theorem prover [7] can be used to detect and prove the absence of the family of errors known as order errors. This is done by taking account of the goals and knowledge of users. We provide an explicit generic user model which embodies theory from the cognitive sciences about the way people are known to act. The user model describes action based on user communication goals. These are goals that a user adopts based on their knowledge of the task they must perform to achieve their goals. We use a simple example of a vending machine to demonstrate the approach. We prove that a user does achieve their goal for a particular design of machine. In doing so we demonstrate that communication goal based errors cannot occur

Modelling rational user behaviour as games between an angel and a demon

Formal models of rational user behavior are essential for user-centered reasoning about interactive systems. At an abstract level, planned behavior and reactive behavior are two important aspects of the rational behavior of users for which existing cognitive modeling approaches are too detailed. In this paper, we propose a novel treatment of these aspects within our formal framework of cognitively plausible behavior. We develop an abstract, formal model of rational behavior as a game between two opponents. Intuitively, an Angel abstractly represents the planning aspects, whereas a Demon represents the reactive aspects of user behavior. The formalization is carried out within the MOCHA framework and is illustrated by simple examples of interactive tasks

PUMA Footprints: linking theory and craft skill in usability evaluation

‘Footprints’ are marks or features of a design that alert the analyst to the possible existence of usability difficulties caused by violations of design principles. PUMA Footprints make an explicit link between the theory underlying a Programmable User Model and the design principles that can be derived from that theory. While principles are widely presented as being intuitively obvious, it is desirable that they should have a theoretical basis. However, working directly with theory tends to be time-consuming, and demands a high level of skill. PUMA footprints offer a theory-based justification for various usability principles, with guidelines on detecting violations of those principles

Verification-guided modelling of salience and cognitive load

Well-designed interfaces use procedural and sensory cues to increase the cognitive salience of appropriate actions. However, empirical studies suggest that cognitive load can influence the strength of those cues. We formalise the relationship between salience and cognitive load revealed by empirical data. We add these rules to our abstract cognitive architecture, based on higher-order logic and developed for the formal verification of usability properties. The interface of a fire engine dispatch task from the empirical studies is then formally modelled and verified. The outcomes of this verification and their comparison with the empirical data provide a way of assessing our salience and load rules. They also guide further iterative refinements of these rules. Furthermore, the juxtaposition of the outcomes of formal analysis and empirical studies suggests new experimental hypotheses, thus providing input to researchers in cognitive science

Interaction design issues for car navigation systems

We describe a study on the interaction design of in-car navigation systems. It focused on a commercial product. Critical incident analysis was performed based on natural use of the system by a usability analyst. A cognitive walkthrough was then performed based on actual scenarios from the natural use. This is a non-classic application of cognitive walkthrough. It allowed anecdotal critical incidents to be theoretically grounded. We draw conclusions about the interaction design of car navigation systems