Effect of Vibration Frequency Mismatch on Apparent Tactile Motion

Abstract

Vibrotactile feedback is increasingly common in our daily life. This growth in haptic feedback usage has produced a demand for higher quality feedback that improves users' experience when they communicate with different devices. The experience of sophisticated haptic feedback could further improve when more than one haptic devices are used simultaneously. A combination of different haptic devices could for example make it possible to feel illusions such as apparent tactile motion and phantom tactile sensations. The apparent tactile motion illusion, in particular, allows the perception of a continuously moving stimulus when two or more non-moving stimuli are produced with specific timing and distance intervals. This illusion could for example create a sensation of flow between multiple haptic devices, such as between a smartwatch and a handheld controller. Questions arise, however, when the haptic devices used are not designed to operate together, as may be the case for commercial products. How does a mismatch in the resonant frequency of two actuators affect the detection of tactile illusions, and more specifically apparent tactile motion? Does this illusion break down as the frequency mismatch increases? While perceptual illusions have been investigated for more than a century, most studies that investigate the influence of parameters on motion perception have assumed that the actuators used at two body locations are identical and therefore produced vibrations with the same amplitude and frequency. We ran two experiments to investigate the effect of mismatching vibratory frequency on the perception of apparent tactile motion. We asked participants to judge the tactile motion direction while the frequency was mismatched, the perceived intensity was normalized, and the distance between actuators and timing parameters were fixed. We simulated having actuators with different properties by changing the frequency and amplitude of the vibration pulses produced by a wide-band actuator. We varied frequencies in a range from 50 to 250 Hz and adjusted the amplitude to normalize the perceived intensity. The results suggest that the apparent tactile motion illusion is robust to mismatches in resonant frequency of actuators and that it can therefore be used with haptic devices manufactured with different specifications.