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Chapter 9 Text Entry by Gaze: Utilizing ... > 9.3 CASE STUDIES AND GUIDELINES - Pg. 181

9.3 Case Studies and Guidelines 181 continuous pointing gestures. At the beginning, the letters of the alphabet are located in a column on the right side of the screen (see Fig. 9.4). Letters are ordered alphabetically (Fig. 9.4, left). The user moves the cursor to point at the region that contains the desired letter by looking at the letter. The area of the selected letter starts to zoom in (grow) and move to the left, closer to the center of the screen (Fig. 9.4, right). Simultaneously, the language model of the system predicts the most prob- able next letters. The areas of the most probable letters start to grow (compared to other, not as probable, letters) within the chosen region. This brings the next most probable letters closer to the current cursor position, thus minimizing the distance and time to select the next letter(s). The letter is typed when it crosses the horizontal line on the center of the screen. Canceling the last letter is done by looking to the left; the letter then moves back to the right side of the screen. Dasher's mode-free continuous operation makes it especially suitable for gaze as only one bit of information is required: the direction of gaze. No additional switches or dwell time are needed to make a selection or to cancel. Furthermore, instead of adding separate buttons or lists with the next most probable words, Dasher embeds the predic- tions into the writing process itself. Many successive characters can be selected by a sin- gle gesture, and often-used words are easier and faster to write than rare words. This not only speeds up the text entry process but also makes it easier: In a comparative