Your users can ́t talk! How can you tell they liked your system?

Assistive technology suitability is extremely dependent on users and their needs. We understand that assistive technology and computer assisted therapy applications, in order to evolve from a stage of prototypes to commercial products, need to be evaluated with users. However, if users are unable to express their opinion, many usability evaluation methods cannot be applied. Our experience with body signals in usability evaluation has shown that it is hard to establish causeconsequence relations from collected data and usability findings. We look for methods that can help designers of assistive technology to evaluate the opinion of nonverbal patients without the mediation of caregivers. In this paper, we raise some of the questions we would like to have answered in the course of this research.