Feeling the Pressure: The Influence of Vibrotactile Patterns on Feedback Perception.

Tactile feedback is necessary for closing the sen-sorimotor loop in prosthetic and tele-operable control, which would allow for more precise manipulation and increased acceptance of use of such devices. Pressure stimuli are commonly presented to users in haptic devices through a sensory substitution to vibration. The precise nature of this substitution affects pressure sensitivity, as well as the comfort and intuitiveness of the device for the user. This study determines the effects of different vibrational encodings for pressure on user-preference and performance in a 4-alternative absolute identification task. 4 different encoding patterns for pressure were examined: short pulse and long pulse amplitude modulation along with sine and square wave frequency modulation. Of the methods examined, frequency modulation methods led to the best discrimination of stimuli (p < 0.001). There was a notable difference in user preference between the two frequency modulated systems, with sinusoidal stimulation being highest ranked across all the preference metrics and square-wave being ranked lowest in two of the three. This difference trended towards, but did not achieve statistical significance (TLX rankings, $p$ = 0.098). This suggests that prostheses or teleoperated devices utilising vibrotactile feedback may benefit from implementing a discrete frequency-based sinusoidal pattern to indicate changes in grip force.