Bubble Cursor Report

The third experiment followed a 4×4×3 within-subjects design with the following factors: Blocks (4 blocks to test learning effect), Technique (Ray-Casting Selection with visual feedback, Bubble Cursor, Expanding Target, Sticky Ray), Number of Distractors (5, 10, 15). As there were 9 (3×3 grid) different locations for each condition and we had twelve participants, a total of 5184 (4×4×3×9×12) trails were logged. As with the previous experiments, by removing 31 trails (~0.5%) as the outliers, we were left with 5153 trails. For each randomly generated trail, the system would test if the goal target was in front or behind a distractor. The overlapping (or occluded) condition would be marked. As the previous two experiments, we recorded the selection time and errors.
We then chose two objects which are closest to the cursor and set the Intersecting Distance (the length of the shortest line connecting the center of the bubble cursor and the second closest object border) and Containment Distance (the length of the longest line connecting the center of the bubble cursor and the closest object border). We set the radius of the bubble cursor to minimum of Containment Distance and Intersecting Distance [26]. When a part of the object is included in the cursor, it would be highlighted and, in such cases, we made sure that there would only be one object being highlighted.
For Expanding Target technique, when the cursor pointed into a certain range surrounding the object, the object would be scaled up to make it bigger (Figure 7b). We implemented Sticky Ray by selecting the closest object to the current position of the