Invented in 1965 to be an economic replacement for light-pens, the mouse remains the primary pointing and selecting device for desktop computers (Myers 4). Mouse position plays a key role in many ergonomics studies in that placement of a mouse can affect user performance. The mouse should be located within arm's reach of the keyboard at a height so that the elbow forms a ninety-degree angle with the shoulders. By positioning the mouse next to the keyboard, it prevents the user from having a twisting or reaching posture (Balin 3). (Balin 3). When working on a computer, the height of the seat should permit the user to have the knuckles, wrist and top of the forearm to form a straight line. (Balin 3). Furthermore, the user should be sitting at a height so that feet are flat on the floor with thighs parallel to the ground and back relaxed against the chair (General Libraries Ergonomics Task Force 5) .
There are a myraid of mice types ranging from one button to three, and mice like the trackball that permit a user to move the cursor across the screen moving a ball placed on top of the mouse (Shneiderman 319-20) . With the trackman, the only desk space needed is where the mouse is actually placed. However, all of these mice involve the tradeoff of desk space. In the case of the moving mice, a mouse pad is needed to provide a surface to move the mouse, resulting in the use of precious desk space. The smaller and more cluttered the deskspace, the less room there is for the user to manuver the mouse on the pad. As a result, the type of mouse a user chooses should optimize performance in the work environment.
Over the years, studies have been conducted evaluating the mouse from the perspective of human performance but few have contributed to developing a general model of human performance (Buxton 1). The Three State Model breaks down mouse movement into three specific states:
Mouse movement primarily exists in states 1 and 2, with the user constantly alternating between the two. Maintaining a constant ease of motion during State 2 is where the biggest potential impediment to performance exists (Buxton 7). Fitts' Law proves essential when predicting movement time of a user during State 2 use (Salvendy 119). The formula for Fitts' law is:
Fitts' law proves excellent in predicting a user's movement time when using a mouse to select an item. However, Fitts' Law does not take into consideration is the size of the user's mouse pad that the mouse is positioned on. If mouse pad is too small, than the user may have to reposition the mouse several times to go from one corner of the screen to the other. On the opposite end, a mouse pad that is too large takes up valuable desk space. Supplying a mouse pad large enough to provide the user with plenty of area movement but small enough to fit economically into a workspace has proved challenging over the years. Commercial mouse pads are roughly 19 3/4" x 21 3/4", although why this particular size was selected is unknown. To avoid using up valuable deskpace, many users have switched over to other types of pointing devices, such as the trackball.
Though the use of mice and the problems associated with their use are so prevalent, the issue of mouse pad dimensions has been all but ignored. A quick scan of commercially available mouse pads includes a number of popular sizes (including 8" x 9.5" and 8.5" x 10") but no standard size. The reasons for the adoption of these popular sizes are unclear. Although the aspect ratios of the mouse pads do not match the aspect ratio of the screens, the mouse pads are large enough to allow traversal of the screen without a State 0 action, and the problems which plague mouse users as discussed above remain. This study investigates the area of mouse pad dimensions, specifically their effects on the performance of users. Three sizes of mouse pads were investigated, with users' time and subjective preferences collected to assess performance and satisfaction.