Perceived Intensity of Pneumatic Vibrotactile Stimuli: Effects of Pressure, Frequency, and Stiffness

Vibrotactile actuators are used in many different haptic devices, e.g. game controllers and smartphones. These vibrotactile actuators are typically made of rigid materials. In this paper, we use soft pneumatic actuators known as Pneumatic Unit Cell (PUC) to characterize the perceived intensity of vibrotactile stimuli when presented at the tip of the index finger. This study investigates how three parameters-stimulus pressure (4 to 30 kPa), inflation-deflation frequency (20 to 100 Hz), and actuator stiffness (determined by top layer thicknesses of 0.9 mm and 1.2 mm)-influence the perceptual intensity of the stimuli. Psychophysical experiments involving 16 participants were conducted using the AEPsych toolbox. These reveal that all the three parameters - pressure, frequency, and actuator stiffness significantly affect perceptual intensity. The findings indicate that both pressure and frequency exhibit a positive main effect and a positive interaction effect on perceived vibrotactile intensity. Additionally, the results show that, for a given frequency, pressure variations produce more perceptually distinct stimuli than frequency variations for a given pressure. Finally, presenting vibrotactile stimuli on a less stiff PUC actuator was perceived as being less intense than when the same stimulus was presented on a stiffer PUC actuator. Overall, this study provides key insights into the combined influence of pressure, frequency and actuator stiffness on the perceived vibrotactile intensity.