Apple Trackpad

The lower layer of interaction in the trackpad is the button level. When you press down, it is the same result as if you clicked a mouse or tapped the trackpad: a mouse-click event is triggered. Since a press of the trackpad and a tap on the trackpad are both registered as the same event, it could be argued that this button level could be removed from the trackpad with no degradation of interaction. It is my thought that the button level was kept in the design to assist in those few occasions when only using a tap can make an interaction more difficult than using a button. Some interactions are more efficient and manually possible through the addition of physicality, instead of attempting to combine a string of touch motions that virtually create the same result.

Two ways of dragging an icon across the desktop (a simplified example):

• Move finger to place cursor on the icon, press down with left finger, use right finger to drag cursor across screen.
• Or, move finger to place cursor on the icon, double-tap finger but hold the finger down on the second tap, move finger to drag cursor across the screen, tap finger again to release the double-tap-hold.

The button level of the trackpad provides access to a single mouse event, click.

Apple Trackpad: button level

The upper level of the Trackpad provides a plethora of interaction that goes beyond the assumed abilities of a typical trackpad. For full disclosure, I must admit that I do not have an Apple Trackpad and am only stating functionality from what I have witnessed or seen online.

All typical interactions are possible: tap, double-tap, drag. Apple expands on these interactions, though, through the use of a multi-touch trackpad: “right-click” when tap with second finger when first finger is already touching, two-finger scroll for a webpage, four-finger up to hide all open applications, four-finger down to show a small icon of each open application, pinch two fingers to zoom, rotate two fingers to rotate an image, hold your thumb down while moving your finger to perform a click-drag, press with two fingers for a “right-click”, three fingers swiped to the left or right to move back or forward while surfing the web, four fingers swiped left or right to open the Application Switcher… and on top of all that… you can customize all of these gestures through a preferences pane in the control panel!

Apple Trackpad: touch level

The Apple Trackpad is not a SUI because it does not contain multiple interfaces. This was not an immediate verdict though. If the definition of “multiple interfaces” were stretched thinly, the answer could almost be “Yes” to the multiple interfaces question.

• The top layer provides cursor movement control, cursor event commands, and access to a limited set of gesture commands.
• The bottom layer provides cursor event commands, too.

Where the definition of “multiple interfaces” could be stretched, and I think where most people are convinced that it is a SUI, is how gestures are incorporated into the overall functionality of the trackpad. Without the gestures, the Apple Trackpad would without a doubt not be a SUI because of the absence of opposed interfaces. The button and touch-sensitivity are both controlling the same interface. With the inclusion of gestures in the top layer of interactions, the line that separates the interfaces becomes blurred, and the definition of “interface” becomes uncertain.

From my inexperienced understanding of the Apple Trackpad gestures, they are simply shortcuts or “quick-keys” to functionality that is attainable by other means. The gesture is providing the user with a quicker way of performing the function by allowing the user to maintain their hand position and not move their arm to press a button, or by eliminating multiple cursor movements and click commands. Because of this, I do not consider the gestures to be an interface. I do admit, though, that more investigation is necessary…

Apple Trackpad: SUI levels