IntroductionThe increasing role of interactive public displays is important because they allow users to employ technology in place of such things as chalkboards and bulletin boards. The ability to use computation in conjunction with a display can allow for easier manipulation of information and an enriched user experience.

However, in the implementation of large public displays, the technology used for interaction can pose a difficult problem. People will want to be able to control and manipulate things on the display, but we do not want users to be tied to a keyboard and mouse, or for them to have to gain access to special equipment in order to use the public displays.

Our solution is to use the number-pad on a mobile phone to select grids on the display, allowing the user to navigate the display by “zooming in”. When users press a number on the phone, the corresponding grid on the display is highlighted and they can choose to zoom in, creating a new and smaller grid. Users can also use the track-stick on the phone for fine-grain navigation.

Materials and methodsSubjects were asked to complete navigation tasks on a large public display (four 52” widescreen displays). Subjects used the GridMouse software running on an iMate SP5m mobile phone and a gyroscopic mouse (Gyration GC15M). The mobile phone transmitted key presses to the computer through WiFi.

Each trial consisted of the exact same distribution of 60 dots but was inverted across the x-axis and the order was reversed to account for any possible learning effects. Circular targets were used because they eliminated any differences that might result from the angle of approach.

ConclusionsInterestingly, even though GridMouse was much slower than the gyroscopic mouse, the subjective ratings of the participants do not indicate a great difference. The subjective results indicate that speed is not always the most important factor in evaluating these devices. Four users preferred the gyroscopic mouse (Users 1, 2, 4, 5) while two preferred GridMouse (Users 3, 6). Beyond these basic preferences, the average ratings for the ease of learning to use each device were equal.

This discrepancy between speed and user satisfaction is indicative of the fact that the speed of the gyroscopic mouse may be hindered by the difficulty of selecting small targets. Several users commented on the sensitivity of the mouse and the overall difficulty of using it. Also, based on observations of the subjects, they all struggled with getting the mouse to hover over smaller targets and frequently overshot the target multiple times.

The problem of accuracy when selecting small targets is almost completely eliminated in GridMouse because the grids make it easy to see how the mouse will move. Additionally, because the track-stick moves slowly and predictably, subjects found that it was much easier to select a target.

Another important issue was the ergonomics of the mobile phone. The buttons on the phone are quite small and close together, and several users made the mistake of pressing the wrong button. It was particularly common for them to press ‘7’ instead of the ‘*’ key when they tried to click on a target. This issue could potentially be resolved by moving the left click key to a more easily accessible button, or by using a different mobile phone with larger buttons.

GridMouse: Using mobile phones to navigate large public displaysAnna Ostberg, Jon Campbell, Brian Evans Advisor: Bill Griswold

Calit2, University of California San Diego, La Jolla, California

Figure 1. Gyroscopic mouse (left), iMate mobile phone (right)

Future workDuring the school year, I will be working on completing an actual user study with 15-20 subjects and writing a paper.

For further informationPlease contact aostberg@ucsd.edu.

Sas, C,. Dix, A. 2008. Designing and evaluating mobile phone-based interaction with public displays. In CHI ’08 extended abstracts on Human factors in computing systems (Florence, Italy, April 05 – 10, 2008). CHI ’08. ACM Press, New York, NY, 3941-3944.

Wobbrock, J.O., Myers, B.A. 2008. Trackball Text Entry for People with Motor Impairments. In CHI ‘06 Proceedings (Montreal, Quebec, Canada, April 22 – 27, 2006). CHI ’06. ACM Press, New York, NY, 479-488.

Related workDouglas, S.A., Mithal, A.K.. 1994. The effect of reducing homing time on the

speed of a finger-controlled isometric pointing device. In Proceedings of the SIGCHI conference on Human factors in computing systems: celebrating interdependence (Boston, Massachusetts, USA, April 24 – 28, 1994). SIGCHI ’94. ACM Press, New York, NY, 411-416.

Nielsen, J., Levy, J. 1994. Measuring usability: preference vs. performance. In Communications of the ACM v.37 n.4 (April 1994). ACM Press, New York, NY, 66-75.

Another important result of the study was seeing what kinds of styles and techniques the subjects developed. This was observed while they completed the tasks. On the gyroscopic mouse, subjects coped with the sensitivity and awkward button positioning by holding the mouse with two hands.

While using GridMouse, on the other hand, subjects developed a number of distinct interaction styles. One such style was to never zoom in. These users chose to use the numbers on the phone to navigate between the 9 grids that are accessible at the largest zoom. Once they had selected the correct grid, they simply used the track-stick to move in the direction of the target. This eliminated the need to zoom-out every time and subjects who used the technique said that it felt faster.

In another style, subjects did use the zooming functionality, but if the next target was outside the current grid but somewhere near the current mouse location, they got as close as they could using the grid and then used the track-stick (Figure 4).

ResultsThe user study was measured both objectively and subjectively. Our objective measure was the time-stamps of every click that the user made. For the subjective portion, participants were also asked to fill out a short questionnaire where they rated the two devices and evaluated their preferences.

The time-stamps are an important part of the study because they indicate how quickly the user is able to complete the task on each device. Figure 3 indicates the total duration of the tasks:

Figure 3. The task completion times for each subject on each device. The dashed red line is the average times. The results from the first participant are not included because the task was not the same length as for users 2 through 6.

The average speeds (minutes:seconds.milliseconds) for the two devices are:

Gyroscopic Mouse: 2:35.925GridMouse: 9:36.148

On average, GridMouse takes 3.695 times as long.

Figure 2. A screenshot of the task that subjects performed on each device.

**Note: Due to time constraints, this preliminary study consisted of only six subjects, and thus is not considered statistically significant.

Following their completion of the clicking task, subjects completed the questionnaire. On this questionnaire, they rated the ease of learning how to use each device, as well as the ease of actually using each device.

Question Average

Ease of learning how to use the gyroscopic mouse 4.33

Ease of learning how to use GridMouse 4.33

Ease of using gyroscopic mouse 3.83

Ease of using GridMouse 3.50

Figure 4. How a user might navigate to the blue target without having to zoom out. The user moves to zone ‘3’ (orange arrow) to get as close to the target as possible, and then uses the track-stick (green arrow).