Motor Skill Learning in User Interfaces

In studying H. M., a 40-year-old patient showing a severe anterograde amnesia, Corkin [3] discovered that despite the patient's inability to remember new information, he was able to acquire new motor skills through repeated practice. His findings supported the theory that a motor skill memory system exists separate from other memory systems. Corkin [3] also states:

In general, retention of a variety of motor skills is very high, even for no-practice intervals of up to two years, and relearning is rapid (for reviews see [1], Chap. 8, and [9]). On the other hand, verbal material is typically forgotten much more quickly [8, 10]. The few instances in which motor learning dissipates rapidly ([1], pp. 267-237; [9]) are those in which the task has a large verbal or other non-motor component.

The fallibility of human memory can be offset by taking advantage of the robustness in motor skill learning.

It can be argued that shortcut keys rely on motor skill learning. Since touch-typing is a motor skill, why do shortcut keys not exhibit the robustness described by Corkin? The problem emerges when the act of typing is contrasted with the act of pressing a shortcut key in a typical RTS game. With typing, users always place their fingers on the "home" keys thereby allowing them to perform each action in a consistent matter. In other words, they learn to type each letter by repeatedly practicing the same motion. With a typical RTS game, the player may approach the key from various angles and positions. Unlike typing, there is no obvious "home" position that allows the player to repeatedly practice the same motion. Thus the player cannot rely solely on his/her motor skill and is forced to use a less robust memory system. Providing a "home" position for the user enhances the motor skill element of the interface learning.

The directional/movement keys are one of the most familiar "home" positions in gaming. Typically (assuming, without loss of generality, the player is right handed), the middle finger is on the up-arrow key with the index and ring finger on the left and right arrow keys respectively. This position can be transposed to other areas of the keyboard (e.g., the WASD keys). On a gamepad, the natural position is the thumb on the directional-pad (D-Pad). Taking advantage of these natural positions activates players' robust motor skill learning mechanisms in the brain.

Motor Skill Learning in Discretized Pie Menus

Many games, most notably "The Sims", now employ a pie menu user interface. It is easy for novice users, who simply follow the menu labels, and remains efficient for expert users, who remember the correct sequence of movements without reading the labels [6]. In addition, novice users do not need to learn a separate input protocol in becoming an expert user. The graphical display is also kept clean since the menu is drawn only when the player performs a menu action. For games requiring a vast number of options, multi-level or hierarchical menus can be used, an example of which can be seen in the Half-life mod, "Natural Selection".

Still, pie menus rely on pointer-based input devices and thus distance and target size become factors of MT. Using directional keys to discretize the menu interface gains the benefit of minimizing MT (do not need to take into account distance and target size) while continuing to leverage the robust nature of motor skill learning. In addition, the interface can be utilized on any gaming platforms. As an example, suppose a player wishes to place a missile turret in a typical RTS game using a gamepad and discretized pie menus. The player might take the following steps (see also Figure 2):

1. Player uses D-Pad to position the cursor at the desired position.
2. Player holds the "menu" button which pops-up a pie menu.
3. The player presses left on the D-Pad to open the "Turret" menu, then presses right to select "Missile Turret."
4. The building is placed. Alternatively, the player can let go of the menu button at any time to cancel the action.

Figure 2: Example implementation of an RTS game using a gamepad. (a) Player positions the cursor. (b) Player opens the menu and selects "Turret Menu" by pressing left on the D-Pad. (c) Player selects "Missile Turret" by pressing right on the D-Pad. (d) The turret is placed.)

The player is able to perform the actions required in RTS games without the aid of a mouse.

Caveats of Discretized Pie Menus