The programmable PalmPilot provides an easy-to-learn interface that can directly access the functionality of the 486 Linux based wearable computer, and be easily stored when not in use. The original design of the affective wearable [PH97] included a Private Eye HUD mounted on lab goggles, a Twiddler chordic keyboard, four physiological sensors: the electromyogram (EMG) , the photoplethysmograph (BVP), (for measuring heart rate and vasoconstriction), the skin conductance sensors (GSR), and a tuned analog to digital converter as shown in Figure 3. In the new design, the PalmPilot interface replaces both the Private Eye and the Twiddler. We developed software (available upon request to researchers) to enable the PalmPilot to communicate with the wearable computer through a serial port.
The primary benefit of the PalmPilot is that it increases the social comfort of the wearer. Additionally, many people are familiar with the handwriting recognition algorithm used by the PalmPilot and find it to be easier to learn to use than chordic keyboards. Although the physiological sensors can be hidden under clothes (as shown in Figure 4), a heads up display and chordic keyboard are more difficult to disguise and can interfere with social interaction.
The social advantages of a tablet-based interface over a heads up display are subtle but important. When the user's eyes are obscured, it is difficult for another person to determine whether the user is attending to them or to the computer (See Figure 2). Even if the HUD is on transparent glasses, it can seem that the computer always has precedence, since a screen change will often inadvertently grab the wearer's attention away from the other person. The PalmPilot interface allows the user's attention to be focused on other people rather than on the computer. By distancing the visual interface, the other person can be the primary focus of the user's attention. The tablet interface also facilitates the social acceptance of the wearable by allowing others to ``glance over the shoulder'' of the user to see what is being written[Bea97]. However, by keeping the tablet out of the view of others, some input can be kept private, even in a public setting, which is an advantage over speech interfaces. This interface provides a low power, low cost solution to wearable interface issues and is especially valuable when the primary task of the computer does not require frequent direct input from the user.