Towards a tool for predicting speech functionality

In these days of multimodal systems and interfaces, many research teams are investigating the purposes for which novel combinations of modalities can be used. It is easy to forget that we still lack solid foundations for evaluating the functionality of individual families of input/output modalities, such as the speech modalities. The reason why these foundations are missing is the complexity of the problem. Based on the study of particular applications, empirical investigations of speech functionality address points in a vast multi-dimensional design space. At best, solid findings yield low-level generalisations which can be used by designers developing almost identical applications. Furthermore, the conceptual and theoretical apparatus needed to describe these findings in a principled way is largely missing. This paper argues that a shift in perspective can help address issues of modality choice both scientifically and in design practice. Instead of empirically focusing on fragments of the virtually infinite combinatorics of tasks, environments, performance parameters, user groups, cognitive properties etc., the problem of modality functionality is addressed as a problem of choosing between modalities which have very different properties with respect to the representation and exchange of information between user and system. Based on a study of 120 claims on speech functionality from the literature, it is shown that a small set of modality properties are surprisingly powerful in justifying, supporting and correcting the claims set. The paper analyses why modality properties can be used for these purposes and argues that their power could be made available to systems and interface designers who have to make modality choices during early design of speech-related systems and interfaces. Using hypertext, it is illustrated how this power may be harnessed for the purpose of predictively supporting speech modality choice during early systems and interface design.