###### Abstract
If a predefined set of short voice commands is used, the interaction loses the advantage of naturalness, and a user may experience difficulty in quickly remembering the right command even after substantial training. Interaction based on learned commands may also be difficult for people with cognitive deficits. Finally, fast and reliable recognition of voice commands is still difficult to achieve. Voice-based selection confirmation in gaze-based communication, however, is a goal different from the goal of enabling rich interaction through the combination of voice and gaze. While the former goal is less ambitious, success could also be of practical importance. For achieving this goal, long, meaningful phrases and sets of predefined words are not needed; instead, any convenient short word or even non-word sound can be used. To our knowledge, however, attempts to create a gaze-controlled interface in which the voice is used just for selection confirmation, without translating any additional information, have not been so far undertaken, probably because the voice is perceived as too good for being used just as a substitute to a mouse click. Moreover, one may expect that, even for a severely paralyzed user, the use of voice just for this goal could be a very boring and unacceptable approach. We suggested that it is, nevertheless, possible to find short words that could be comfortably and effectively used simply as a selection operation in gaze-based interaction. For testing this hypothesis, we added a simple, word-insensitive voice-based selection confirmation to our experimental platform ([22], [PERSON] et al., under review). This platform presents experiment participants with moving objects that they should select using their smooth pursuit eye movements, which are detected using an eye tracker. Selection based on smooth pursuit has been developed in recent years as a powerful variant of gaze-based interaction [23; 24; 25; 26; 27; 28], and it was shown that gaze-based selection can even be made faster than mouse-based selection in the case of selecting moving objects [22]. We designed an experiment, in which healthy participants were asked to make, as fast as possible, multiple selections using gaze and simple uniform voice command. In preliminary experiments, we found that the use of some words for confirmation indeed poses usability problems to quite many users. Participants often reported that they feel too strange to use the word \"yes\" (pronounced as \"da\" in Russian) many times in the row (or found it too funny). Pronuncing the names of the letters of the alphabet printed on the objects to be selected was typically found to be a simpler way of selection confirmation; however, some letter names appeared to be too long, and some participants faced difficulties because they could not quickly remember the standard naming of some letters. For the systematic study described further in the paper, we decided to choose three ways of voice confirmation of the gaze-based object selection, which appeared to be more comfortable to the participants in pilot experiments: (a) Using the word \"you\" (pronounced \"ty\" in Russian), (b) naming the numbers typed on the objects, (c) using a short word which they themselves found to be comfortable to them, based on their experience with (a) and (b) methods. In separate runs, participants used the manual button press as a confirmation of the gaze-based selection. An inexpensive, consumer-grade eye tracker was used, to provide fairer modeling of technology use.