Mechanical Vibration Influences the Perception of Electrovibration

Abstract

Recently, various methods using, simultaneously, two types of tactile feedback have been proposed to emulate a real object. However, the possible masking effect when providing two types of tactile feedback has been scarcely reported. In this study, we investigated the masking effect caused by mechanical vibration on the perception of electrovibration. The absolute and difference thresholds of the electrovibration were measured according to the presence/absence, frequency, and intensity of the mechanical vibration. The absolute threshold of electrovibration tended to increase in the form of a ramp function, as the intensity of the masking stimulus (mechanical vibration) increased. Particularly, the masking effect was more remarkable when the frequency of both the target and the masking stimulus was the same (up to 13 dB increase with 25 dB SL masker). Furthermore, the difference in the threshold (average of 1.21 dB) did not significantly change due to the masking stimulus, when the sensation level intensity of the target stimulus was within the section following the Weber's law. The results further indicated that electrovibration contributes to the activation of slowly adapting afferents as well. This investigation will provide important guidelines for the design of haptic interface that employs multiple types of tactile feedback.

Figure 1

Absolute thresholds (AL) of electrovibration (EV) and mechanical vibration (MV). (a) Mean absolute threshold of electrovibration for three test frequencies with standard error bars (filled circle, left axis) and the absolute threshold curve of the tangential force, as obtained by Israr et al. (dashed line, right axis). The open-star symbol, which was not used for analysis, denotes the roughly estimated absolute threshold of electrovibration at 400 Hz, as obtained from a pilot test. (b) Mean absolute threshold of mechanical vibration for three test frequencies with standard error bars (filled circle, left axis) and the absolute threshold curve of acceleration, as obtained by Morioka et al. (dashed line, right axis).

Figure 2

Changes in the absolute threshold (AL) and difference threshold (DL) of electrovibration (EV) in the presence of mechanical vibration (MV). (a) Mean changes in the absolute threshold of EV at 270 Hz under masker conditions (120, 180, and 270 Hz with 5–25 dB SL) with standard error bars. To evaluate the masking effects, the unmasked ALs of EV at 270 Hz in Experiment 1 were subtracted from the corresponding masked ALs, which were measured in Experiment 2. Asterisks denote that the data column is significantly different from zero (p < 0.0.05). (b) Mean changes in the difference threshold of EV at 270 Hz under masker conditions (120, 180, and 270 Hz with 10 dB SL and 20 dB SL) with standard error bars. To evaluate the masking effects, the unmasked DLs of EV at 270 Hz were subtracted from the corresponding masked DLs.

Figure 3

Hardware setup for generating both electrovibration and mechanical vibration stimuli.

Figure 4

Stimulus sequence within a three-interval, forced-choice (3IFC) paradigm. (a) Stimulus sequence in Experiment 1. (b) Stimulus sequence in Experiment 2. (c) Stimulus sequence in Experiment 3. (d) Sliding speed and distance in each interval during the experimental run.