Our interest in human–computer interaction started with our participation in the TT2 project (“Trans–Type-2”, 2002–2005—http://www.tt2.atosorigin.es), funded by the European Union (EU) and coordinated by Atos Origin, which dealt with the development of statistical-based technologies for computer assisted translation.

Several years earlier, we had coordinated one of the first EU-funded projects on spoken machine translation (EuTrans, 1996–2000—http://prhlt.iti.es/w/eutrans) and, by the time TT2 started, we had already been working for years in machine translation (MT) in general. So we knew very well which was one of the major bottlenecks for the adoption of the MT technology available at that time by professional translation agencies: Many professional translators preferred to type by themselves all the text from scratch, rather than trying to take advantage of the (few) correct words of a MT-produced text, while fixing the (many) translation errors and sloppy sentences. Clearly, by post-editing the error-prone text produced by a MT system, these professionals felt they were not in command of the translation process; instead, they saw themselves just as dumb assistants of a foolish system which was producing flaky results that they had to figure out how to amend (the state of affairs about post-editing has improved over the years but the feeling of lack of control persists).

In TT2 we learnt quite a few facts about the central role of human feedback in the development of assistive technologies and how this feedback can lead to great human/ machine performance improvements if it is adequately taken into account in the mathematical formulation under which systems are developed. We also understood very well that, in these technologies, the traditional, accuracy-based performance criteria is not sufficiently adequate and performance has to be mainly assessed in terms of estimated human–machine interaction effort. In one word, assistive technology has to be developed in such a way that the human user feels in command of the system, rather than the other way around, and human-interaction effort reduction must be the fundamental driving force behind system design. In TT2 we also started to realize that multimodal processing is somehow implicitly present in all interactive systems and that this can be advantageously exploited to improve overall system performance and usability.