Investigating Multi-Touch Vibrations on Mobile Touchscreens

While many advanced haptic devices are under development, touchscreens are one of the most readily available platforms. In this paper, we leverage a leap forward in vibration-based haptics, Apple's new CoreHaptics API, and investigate its potential for a multi-finger vibration experience. We present a perceptual user study (N=15) that investigates multi-finger vibration identification and exploration strategies and we conduct a laser doppler vibrometry study, uncovering the challenges of developing consistent, high-quality vibration feedback across hardware platforms that vary in actuation principle, screen size, and external attachments. Repeated-measures ANOVA tests showed no statistically significant results in time, error, or weighted error for vibration identification across all participants based on number of fingers. However, one-way ANOVAs did show significant results within individuals, illustrating benefits of multiple-finger exploration. The most effective strategies for locating vibrations involved multiple fingers grouped together using sweeping motions across the screen. Our LDV study demonstrated that CoreHaptics and the Taptic Engine in the iPhone were capable of more accurately recreating specific frequencies than coin motors in Android devices. This research supports a move to a multi-finger, vibrotactile touchscreen experience, while highlighting the challenges of creating a consistent vibration experience across hardware platforms.