Command composition approach in crossing interfaces. with more than two continuous goals

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1 Some Student November 30, 2010 CS 5317 Command composition approach in crossing interfaces with more than two continuous goals 1. INTRODUCTION Over the last decade, pen and touch-based interactions began to play an increasingly important role in the design of user interfaces. They are the interaction style of choice for a variety of devices that include cell phones and tablet computers. A pen or touch-based interaction is well suited for accessing and inputting information from and into cell phones and tablet computers. Additionally, its ease of use on such devices gives it a clear advantage over point-andclick interaction. This is because point-and-click interactions take the desktop or laptop configuration as their base design. Researchers tested the command composition approach on crossing-based interfaces using two continuous goals [Apitz, Guimbretiere and Zhai, 2010]. Although they succeeded, they did not test with more than two goals. The main claim of this paper states that if the experiment team increments the number of continuous goals to three or more, the command composition approach would succeed. I organized the rest of this paper as follows. In section two, I will survey the foundations of crossing-based interfaces, the interaction paradigms. In section three, I will talk about the characteristics of goal-crossing tasks, which are the base of crossing-based interfaces. In section four, I will describe the challenges posed by crossing-based interfaces and possible solutions to those problems. In section five, I will describe command composition and its affect on novice users over time. To conclude, I will comment on some of the questions that remain open in the field of crossing-based interfaces design.

2 2. FOUNDATIONS OF CROSSING-BASED USER INTERFACES Point-and-click consists of moving a cursor to a graphical object using an input device and clicking a button. This sequence represents the basic interaction system for the design of interfaces. In contrast, the idea behind crossing-based interfaces is simple. Users cross a target or goal on the screen to activate an action that is associated with a given object [Apitz, Guimbretiere and Zhai, 2010]. Point-and click has been the dominating paradigm of interaction. It was not until over a decade ago, when research from different areas began experimenting with different paradigms of interaction. These research efforts proposed gesture-and-sweep as a new paradigm for interaction [Winograd and Guimbretiere, 1999]. This paradigm introduced the concept of action bars, which triggered an action as a double click does on a point-and-click interface. Although uncharacteristic, some commercial software systems (including Lotus Notes) used crossing interaction methods. However, it was not until recently that systems started challenging the use of point-and-click interfaces. Modern interfaces already use crossing events to detect enter or leave events. In Lotus Notes, users are able to select multiple s by crossing their header in a designated area. This action demonstrates a goal-crossing task, which is the process of moving a cursor beyond the boundary of a targeted graphical object [Accot and Zhai, 2002]. Users are able to cross in two ways. The first way to cross is continuous crossing, which is when the users are able to continuously strike through the goals if there is nothing between them. The second way is discrete crossing, which is when the users land the pointing object before the intended goal then cross it. This is because there are distracters (non-target objects) between the individual goals.

3 3. BENEFITS OF USING GOAL-CROSSING TASKS Crossing affords a set of unique characteristics because it is a continuous action, which occurs more often in the natural world than discrete point-and-clicking [Accot and Zhai, 2002]. The first distinctive attribute that crossing affords is that it can be bi-directional. This implies that it is feasible to double cross a goal (back and forth once) or even more to indicate different commands. Bi-directionality provides an advantage to goal crossing because contrary to pointand-click, it allows multiple meaning or actions to a single goal or object. In point-and-click, an object has one meaning only. Goal crossing, then, is a step towards free gesturing, which is even richer but harder to measure and clarify than crossing [Accot and Zhai, 2002]. The second distinctive attribute that goal crossing affords is that users are able to cross multiple goals continuously. As I stated above, modern software products like Lotus Notes use this feature to select multiple messages by one continuous cursor drag, crossing through a series of implicit goals. In Lotus Notes, users are able to select a set of continuous messages, and then deselect the messages they do not want to select. In comparison, using the point-and-click alone to select various messages requires very precise and repetitive point-and-click actions. It is worth mentioning that point-and-click and goal crossing must not be mutually exclusive. In fact, it is possible to build a double-representative interface, which enables both actions [Accot and Zhai, 2002]. The industry section that benefits the most from crossing-based interfaces (goal-crossing paradigm) is the mobile or handheld devices design field. Cell phones or tablet computers usually use a stylus or a finger as a means for interaction. These interaction objects are more suited for crossing actions than a regular computer, which in most cases uses a mouse for interaction [Accot and Zhai, 2002]. 4. CHALLENGES POSED BY CROSSING-BASED USER INTERFACES AND POSSIBLE SOLUTIONS Slipping is a problem for users of crossing-based interfaces. It occurs when the user taps with a pointing device (either finger or stylus) and misses its intended target by generally few pixels

4 [Moffatt and McGrenere, 2007]. Currently, there are two approaches to prevent slipping the freezing and the area-cursor strategies. The first approach helps the user by freezing the cursor at the mouse-down position. With the second approach, it is not the tip of the cursor that defines the object selected, but a larger selection area centered on the tip instead. This small degree of separation provides the flexibility needed to allow a natural form of freezing. Another problem that users of crossing-based interfaces confront is drifting, which is when a user switches menus by hovering. The simplest way to prevent this is to turn-off the ability to switch by hovering. Although this clearly fixes the problem, it may interfere with other types of menu interaction. This specifically refers to the case where users are intentionally browsing through menus for an item. Another approach to solve the drifting problem is to introduce a delay to the menu switch while hovering. Designers may implement this strategy with a time delay such that if the pointing device is only briefly hovering over another menu, it does not switch. The third problem that users of crossing interfaces face is missing just below the target. This error occurs when users hit the top of the item just below the intended target. There are two possible ways of modifying the interface to prevent these errors. The first solution is to shift the target region of each item by a couple of pixels. The visual appearance remains unchanged. This implies that the interface interprets any selection on the top region of the item as a selection of item above and triggers its execution. The second solution is to deactivate the top couple of pixels of all menu items. This implies that the interface would ignore each tap on this region [Moffat and McGrenere, 2007]. 5. COMMAND COMPOSITION Designers that base their interface design on the goal-crossing paradigm promote the fluid composition of commands, which enables users to issue several actions with a single stroke. In goal crossing interfaces the direction in which the user crosses the goal matters. It may also hold information about the crossing. The feature of command composition is a unique and significant

5 aspect of the goal-crossing approach that enables users to move easily from novice to experts. Novice users perform one command at a time and heavily rely on visual feedback. As they become more proficient, the users begin to remember the shape of the commands. Users may perform each command composition or combination in separate steps. This reduces the cost of making a mistake while performing a long sequence of actions [Apitz, Guimbretiere and Zhai, 2010]. It is early to judge if the command composition approach is successful when designing goalcrossing interfaces. Previous implementations demonstrate how crossing may ease interactions. Goal crossing is a tool that designers may use to build the ideal interaction system. It enables novice users to discover the interface and train themselves [Apitz, Guimbretiere and Zhai, 2010]. At some point, users will be able to remember the shape of the gesture well enough to generate it on top of the interface elements without the need for visual feedback. The application of the command composition approach is of great impact to interface designers. They should consider the following recommendations when designing goal-crossing interfaces. Designers should position highly used crossing targets on an orthogonal position to the movement. The difficulty of reaching a crossing path increases as it deviates from the horizontal [Apitz, Guimbretiere and Zhai, 2010]. This implies that designers should place the most frequently used sequences of commands on a more or less horizontal path. Additionally, the design should provide enough space to allow recovery for missed crossing during continuous target selection. 6. CONCLUSION The study reviewed the foundations of crossing interfaces, the interaction paradigms, and the characteristics of goal-crossing tasks. It also described common challenges posed by crossing interfaces and possible solutions to them. In this section, I will highlight the implications and compare the possible outcomes of applying these solutions concerning the main claim, which

6 states that if the experiment team increments the number of continuous goals to three or more, the command composition approach will succeed. The potential for success of the command composition approach is high [Apitz, Guimbretiere and Zhai, 2010]. However, previous work bases this conclusion on experiments that used trivial tasks. This suggests that if researchers changed the nature of the tasks and add complexity to them, the results could be unexpected. This issue remains unanswered and I consider it highly relevant to the success of implementing the command composition approach on crossing-based interfaces. Freezing is a proposed solution for the slipping problem [Moffat and McGrenere, 2007]. This solution lacks an analysis of how great the impact of freezing inactive space is. Users usually take advantage of this space using it as a landing space. This solution might not be as effective as it first seems. For the drifting problem, previous work proposed a time delay as the solution [Moffat and McGrenere, 2007]. Although this might solve this problem, time delay also increases the interface s response time when a user intentionally wants to switch menus. Is the risk worth taking? It is a concern that designers must take into consideration. The field needs researchers to answer these open questions. If research solves these issues, then interface designers will succeed when implementing the command composition approach on more than two continuous goals.

7 References Accot, J., Zhai, S. (2002). More than dotting the i's -- foundations for crossing-based interfaces. In Proceedings of the SIGCHI conference on Human factors in computing systems: Changing our world, changing ourselves (CHI '02). ACM, New York, NY, USA, Accot, J., Zhai, S. (2003). Refining Fitts' law models for bivariate pointing. In Proceedings of the SIGCHI conference on Human factors in computing systems (CHI '03). ACM, New York, NY, USA, Apitz, G., Guimbretiere, F., Zhai, S. (2010). Foundations for designing and evaluating user interfaces based on the crossing paradigm. ACM Trans. Comput.-Hum. Interact. 17, 2, Article 9 (May 2010), 42 pages. Moffatt, K., McGrenere, J. (2007). Slipping and drifting: using older users to uncover pen-based target acquisition difficulties. In Proceedings of the 9th international ACM SIGACCESS conference on Computers and accessibility (Assets '07). ACM, New York, NY, USA, Ren, X., Moriya, S. (2000). Improving selection performance on pen-based systems: a study of pen-based interaction for selection tasks. ACM Trans. Comput.-Hum. Interact. 7, 3 (September 2000), Winograd, T., Guimbretiere, F. (1999). Visual instruments for an interactive mural. In CHI '99 extended abstracts on Human factors in computing systems (CHI '99). ACM, New York, NY, USA,

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