It has always been an issue that when a user interacts with a mobile touch device, there is no haptic feedback.
Vibro-tactile feedback could be a single solution but this is somewhat limited since most of the mobile device only has one vibrator.
In this research, 4 vibrators are used to give the user more information by vibro-tactile feedback using perceptual illusion sensation such as saltation and funneling effect.
Feedback was expanded to 2 dimensional area, the location and the direction where vibration occurs was modeled and verified by experiment. APCHI2012 video
Youngsun Kim, Jaedong Lee, and Gerard J. Kim “Extending “Out of the Body” Saltation to 2D Mobile Tactile Interaction” APCHI 2012 APCHI2012 paper