Insights into human perception of asymmetric vibrations via dynamic modeling

Certain ungrounded asymmetric vibrations create a unidirectional force that makes the user feel as though their fingers are being pulled in a particular direction. However, although researchers have discovered this haptic feedback technique and showcased its success in a variety of applications, there is still little understanding about how different attributes of the asymmetric vibration signal affect the perceived pulling sensation. Our work aims to use dynamic modeling and measurement to bridge this gap between the design of the control signals and human perception. We present a new dynamic model of a common vibrotactile actuator (Haptuator Mark II) held between the soft, nonlinear fingers of a human user. After anecdotally observing that actuator acceleration strongly depends on grip force, we augmented this model so that grip force directly modifies the model parameters related to finger contact. We present results from driving this simulation with widely varying asymmetric vibrations that produce stronger and weaker pulling sensations. We also present preliminary data from a user study in which participants rated the perceived direction and strength of the same diverse range of asymmetric vibration cues; grip force and actuator acceleration were both recorded for all trials. Comparing the simulations with the physical measurements and perceptual results validates our dynamic model and provides insights on how different aspects of the asymmetric waveform affect the perception of the pulling sensation.