Optimizing Tactile Feedback for Virtual Buttons in Mobile Devices

Touchscreen mobile devices, which do not have a physical keypad or keyboard, have become very popular. In these devices the interaction is done primarily with virtual buttons as all or most of the physical buttons have been removed. Due to this fact these devices have one major weakness compared to the traditional mobile devices: the lack of tactile feedback. This makes the mobile device usage challenging as the user can only rely on visual and audio feedback. Mobile devices are often used in situations where the user cannot devote all his visual attention to the device and the audio feedback cannot be heard. Therefore the absence of the tactility makes the mobile device usage difficult. Adding tactile feedback to touchscreens might solve this problem. This thesis researches how to design and implement tactile feedback for virtual buttons with the highest level of usability. The research compares two different actuators for producing tactile feedback on the touchscreen: a standard vibration motor and a piezo actuator. The virtual buttons enhanced with tactile feedback features produced with the aforementioned technologies are compared in terms of usability attributes. The usability evaluation is performed using a traditional usability testing method where one participant at a time is doing a pre-defined task with the system. Several studies are conducted including both laboratory and field tests. The results of the studies show that virtual buttons with piezo feedback provide the highest level of usability. With piezo feedback users performed faster and made fewer errors. The results also found the piezo feedback to be the most pleasant tactile feedback on virtual buttons. Virtual buttons with vibra feedback are the second best option in terms of usability. Virtual buttons without tactile feedback have clearly the lowest level of usability. The results also show that when users are on the move, especially when traveling on the metro, the tactile feedback is even more beneficial.

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