Effects of Waveform, Time Delay, and Vibration Axis on the Perception of Vibrotactile Compliance Illusions on Smartphone Touchscreens

A hard surface feels soft or elastic when carefully controlled vibrations are provided to a pressing finger. This compliance illusion method may be employed to augment graphical objects on smartphone screens with compliant tactile properties. However, product engineers encounter practical questions when attempting to use the compliance illusion method for their products. Should the waveform be sinusoidal? How much time delay is acceptable? Should the vibration axis be perpendicular to the surface? A series of experiments was conducted to address these questions. The first experiment revealed that the waveform could not be distinguished in the context of the compliance illusion method when applied to typical smartphones. The second experiment demonstrated that time delays greater than 25 ms and the use of the three vibration axes could be distinguished in the same context. The third experiment explored how the perceptual qualities of the compliance illusion change with variations in time delay and the axis of vibration. Time delay had significant effects on softness, smoothness, elasticity, and unpleasantness, while the vibration axis had significant effects on softness, smoothness, and elasticity.